INFLUENCE OF ACID SECRETORY STATE ON THE GASTRIC MUCOSAL TOLERANCE TO BACK DIFFUSION OF H+

Transcription

1 GASTROENTEROLOGY 71: by The Williama & Wilkin. Co. Vol. 71. No. fi Printed in U.s.A. INFLUENCE OF ACID SECRETORY STATE ON THE GASTRIC MUCOSAL TOLERANCE TO BACK DIFFUSION OF H+ PAUL O'BRIEN, M.B., AND WILLIAM SILEN, M.D. Department of Surgery, HarlJard Medical School and Beth Israel Hospital, Boston, Massachusetts The effect of back diffusion of H+ on the potential difference (PD), eledrical resistance (R), and short circuit current (Isc) of spontaneously secreting and burimamide-inhibited amphibian gastric mucosae were studied in vitro. When back diffusion ofh+ was induced by the passage of an electrical current of 510 Ila per cm 1 from the secretory (S) side of ph 2.25 to the nutrient side (N) for 30 min, the spontaneously secreting mucosae showed small decreases in PD ( mv) and Isc ( la per cmt) but no significant change in R. In the burimamide inhibited mucosae there were marked and significantly greater decreases of PD ( mv), R ( ohms cm I) and Isc (50-131la per cm '). When back diffusion of H+ was induced by establishing a concentration gradient of H+ from S... N or by exposing the secretory surface to sodium taurocholate with secretory ph 2.25, the burimamide-inhibited tissue demonstrated significantly greater depression of the electrical parameters than the secreting mucosae. Intracellular ph, measured by the 5,5-dimethoxyazolidine-2,4-dione method, was significantly higher in the histaminestimulated tissues (7.28) than in the metiamide-inhibited tissues (7.11). These studies strongly suggest that the secretory status of the mucosa and hence its acid-base status are important determinants in the tolerance of the tissue to exogenous back diffusion of H+. The measure of absolute loss of H+ from the mucosal solution alone may not be an adequate assessment of the gastric mucosal barrier. Previous studies of the effects of exogenous agents on the gastric mucosa have emphasized the importance of an increase in the rate of back diffusion of H+ in the pathogenesis of mucosal disease. 1 However, recent studies of hemorrhagic and endotoxic shock" I have shown that ulceration may occur in the absence of an absolute increase in back diffusion of luminal H+. That the functional capacity and functional state of the gastric mucosa are important in maintaining the integrity of the tissue is suggested by the fact that ischemia'" and a deficiency of energy metabolites' have been strongly implicated in the genesis of ulceration. The influence of the secretory state of the gastric mucosa on its response to back diffusion of H+ has not been established. Several workers'" have studied the effect of histamine stimulation of acid secretion on ionic fluxes in canine stomach, but differing results were obtained. All noted a decrease in Na+ output into the lumen during stimulation. Wlodek and Leach' assumed that luminal Na+ gain was equal to H+ loss and concluded that back diffusion of H+ was decreased by histamine. This suggestion was supported by Altamirano,' who studied back diffusion of H+ from exteriorized chambered segments of resting and stimulated Received January 30, Accepted May 7, This paper was presented in part at Surgical Forum of American College of Surgeons, San Francisco, California, October, Supported by United States Public Health Service Grant AM canine gastric mucosa. He calculated that there was cessation of back diffusion of H+ during histamine stimulation, but the assumption was made that the acid secretory rate during periods of acid instillation was equal to that during a preceding period when pure secretion was obtained. Moody and Davis,' however, using a similar experimental technique but deriving acid secretory rate from the acid output of a parallel hemichamber, found an increase in back diffusion of H+ during both stimulation of acid secretion with histamine and secretory inhibition by thiocyanate. These workers also noted that histamine infusion after inhibition by thiocyanate further increased luminal H+ loss and Na+ gain and led to gross disruption of the mucosal surface. All of these studies have focused on the effects of acid secretion on the absolute rate of back diffusion of H+ from the luminal solution. We have found no reports in which direct measurements of the functional integrity of the mucosa have been used to assess the influence of acid secretory activity upon the ability of the tissue to withstand back diffusion of H+. Methods Bullfrogs (Rana catesbeiana) were used for all experiments. They were kept at 10 C in 120 mm NaCl solution and were generally used within 1 week of purchase. For each experiment the frog was pithed, the stomach was removed, and the mucosa was separated from the muscle coats by sharp and blunt dissection. Fundic mucosa was then mounted between the two halves of a Lucite chamber. The exposed mucosal surface

2 November 1976 TOLERANCE TO BACK DIFFUSION 761 measured 1.96 cm". The mucosa was immediately exposed to the bathing solution, which was aerated and circulated with a gas mixture of 95% 0.-5% CO. to both sides of the tissue. The mucosal bathing solution contained 120 mm NaC!. In some experiments this solution was acidified to ph 2.25 by the addition of approximately 0.1 ml of 1 N HC!. The serosal bathing solution contained 87 mm NaCl, 18 mm NaHCO., 4 mm KCl, 1 mm KH.PO o, 1 mm MgCl., 2 mm CaCl., and 10 mm glucose. The circulating volume on each side was 12 m!. The ph of the secretory solution was maintained at either 6.0 or 2.25 by the titration of either 0.05 M NaOH or 0.05 M HCl using a ph stat (Radiometer, Copenhagen, Denmark). This technique was accurate at ph 6.0, but at ph 2.25 it overestimated the rate of change of acidity by approximately 11 %. '0 The ph of the nutrient fluid was approximately The transmucosal potential difference (PD) was measured between two agar bridges (1 M NaCI in 4% agar) connected through calomel reference electrodes to a voltmeter and a recorder. Current was passed across the tissue between two other agar bridges which were connected via Ag-AgCl electrodes to a 45-volt battery. A microammeter measured current flow. The geometry of the cham ber was such that the change in current density from the center to the periphery of the tissue did not exceed 6%. The electrical resistance (R) was calculated from the change in PD at 0.5 sec after passage of a current across the tissue. Correction was made for the fluid resistance (approximately 45 ohms cm'); this was calculated from the change in PO after passing a similar current across the fluid-filled chamber with no tissue present. The short,. circuit current (lsc) was that current required to reduce the PD to zero after allowing long time-constant transient changes in PO to stabilize (90 to 120 sec). The mucosae were permitted to secrete spontaneously or were completely inhibited by the addition of burimamide, 4 mm, to the nutrient solution (N). In some experiments this inhibited state was reversed by the addition of histamine (4 x 10-0 M) to N in the presence of burimamide. A period of at least 60 min for stabilization was allowed between each of the experimental steps. The effects of burimamide on the acid secretory rate were noted at ph 6.0, and only those tissues which had complete inhibition of secretion within 60 min of the addition of burimamide were used. The response of the secreting and nonsecreting gastric rnucosa was studied under three general circumstances: (1) the application of an electrical current from (S) to (N) with and without a concentration gradient of H+ from S... N; (2) establishment of a concentration gradient of H+ from S -+ N; (3) addition of sodium taurocholate to an acid secretory solution. Application of current in the presence of a concentration l ~ a gradient of H+. An electrical current of 510 ~ per a cm was Passed from S -+ N for 30 min at a secretory ph of 6.0 ([H +) = 1 Eq per liter) or at With H+ present in the secretory SOlution (at ph 2.25, [H+) = 6.5 meq per liter), the current would drive protons into the mucosa (see Discussion), whereas at ph 6.0 no appreciable back diffusion of H+ would occur. Cornparison of effects was made in the spontaneously secreting and the burimamide-inhibited tissue. The electrical parameters were noted immediately before passage of current and 30 rnin after cessation of current flow. To ascertain whether the effect of back diffusion of H+ in the inhibited mucosa was due to its nonsecreting status or to a specific effect of the burirnamide, histamine (4 x 10-0 M) was added to the nutrient solution of mucosae inhibited by burimamide and secretion was reestablished without removal of the burimamide. The effect of current was then studied in these tissues at a secretory ph of Gradient-induced back diffusion of H+ (without current). The secretory ph was lowered to 2.25 by the addition of 0.1 ml of 1 N HCl, exposing the mucosal surface to approximately 6.5 meq per liter of H+. The electrical measurements were then made for 3.5 hr. The response of the spontaneously secreting tissues (n - 8) was compared with the response of the burimamide-inhibited mucosae (n = 5) and with the response of mucosae stimulated to secrete by the addition of histamine after inhibition by burimamide (n - 3). Taurocholate-induced back diffusion of H+ (without current). In mucosae that were either secreting spontaneously (n - 7) or were inhibited by burimamide (n = 5), the secretory solution was acidified to ph 2.25 and the tissues were permitted to stabilize. Sodium taurocholate, 10 mm, was then added to the secretory fluid. After 30 min of exposure to sodium taurocholate the secretory solution was replaced with an acid solution (ph 2.25) contain'ng no sodium taurocholate and the tissues were permitted to restabilize. Steady state values for the electrical parameters before onset and 30 min after cessation of exposure to sodium taurocholate were noted. Measurement of intracellular ph. The gastric mucosa was prepared and mounted in the Lucite chamber as for the other experiments. The reservoirs of each hemichamber were interconnected so that the same fluid perfused both sides. Twentyfive milliliters of the HCO, - buffer solution containing 5 ~ of c 5,5-dimethyloxazolidine-2,4-dione-2- u C (OMO) and 25 ~ of c 'H.inulin methoxy per liter (New England Nuclear, Boston, Mass.) were aerated and circulated with 95% 0.-5% CO. and permitted to bathe the tissue for 2 hr at room temperature (approximately 21 C). The ph of the bathing solution was noted. Studies were carried out in spontaneously secreting tissues (n = 12), during exposure to histamine, 4 x 10-0 M (n = 11), and during inhibition with 2 mm metiamide (n = 10). Antral mucosae (n = 10) were also investigated under standard conditions. The mucosa was removed from the chamber and all epithelium was scraped from the subepithelial connective tissue, using a glass slide. The scrapings were weighed, dehydrated in a desiccator overnight, and reweighed to give the total water content of the sample. The tissue was then rehydrated and solubilized with 1 ml of Protosol (New England Nuclear) at 50 C for 12 hr. Fifteen milliliters of Bray's scintillation solution" were added to the dissolved sample and to a O.5-ml sample of the bathing solution. The "H and "c activity of both samples were measured in a liquid scintillation counter (Nuclear-Chicago, Des Plaines, Ill.) using the twochannel technique. All samples were corrected for quenching by the use of internal standards of 'H-toluene and "C-toluene (New England Nuclear). Disintegration rates were calculated by the formulation of Herberg. II The pk' of DMO at 21 C was calculated to be 6.36 from the partition of "C-DMO between 50% ethyl acetate 50% toluene and phosphate buffer solutions of ph 5.7, 6.3, and 6.7, using the method of Butler. II Using the derived values for DMO and inulin content of the tissue, and the calculated pk' of DMO, the intracellular ph of the gastric epithelial cells was calculated by the method of Waddell and Butler." Statistical analysis of the data was performed using Student's t-test for paired and unpaired values. Results Application of current with and without a concentration gradient of H +. The changes induced by the passage

3 762 O'BRIEN AND SILEN Vol. 71, No.5 of an electrical current (510 pa per cm IS... N for 30 min) on the electrical measurements and the net H+ output of five groups of mucosae are shown in tables 1 and 2. At secretory ph 6.0 (table 1) the spontaneously secreting tissues showed small but significant increases in PD, R, and Isc, whereas H+ secretion decreased by 27%. The inhibited mucosae showed no significant changes in electrical measurements after passage of the current. The initial PD and Isc were similar in both groups but the resistance of the inhibited tissues was significantly higher than that of the spontaneously secreting tissues (P < 0.001), a well recognized effect of burimamide. When acid (6.5 meq per liter; ph 2.25) was present on the secretory side (table 2), the secreting tissues (groups III and V) showed a significant fall in the PD and Isc and a small net loss of H+ from the secretory solution. The resistance of these two groups of secreting tissues was not significantly depressed. The same response to the passage of current was observed whether the tissues were secreting spontaneously or had been stimulated to secrete by the addition of histamine after inhibition by burimamide. It should be noted that in group V (burimamide and histamine), addition of the histamine to the tissues already completely inhibited by burimamide restored the H + secretion to 2.6 ± 0.34 peq per cm 2 per hr. The secretory rate of 0.92 ± Oo4pEq per cm 2 per hr was observed after reduction of the ph of the secretory solution to 2.25 and immediately before passage of the current. The passage of current across the inhibited mucosae with secretory ph 2.25 (group IV) was associated with highly significant depression of all electrical parameters and a marked increase in the rate of loss of H+ from the secretory solution. In 5 of these 10 tissues the PD was either zero or reversed in sign and no Isc was measurable at 30 min after cessation of the applied current. In 7 of the 10 mucosae followed over the subsequent 60 min, there was minimal improvement in the electrical parameters. The PD increased by a mean of 104 mv, R increased by 17 ohms cm 2, and there was no change in the Isc. The changes in the PD and R of the inhibited mucosae, shown in table 2, were significantly greater than the corresponding changes in the secreting tissues (groups III and V; P < 0.001). The change in the Isc in group IV was highly significantly greater than the change of Isc of the spontaneously secreting mucosae, but was not significantly different from the change of Isc in group V. Gradient-induced back diffusion of H+. The effect on the electrical parameters of exposure of the secretory surface to acid solution (ph 2.25) for 31/2 hr is shown in figures I, 2, and 3. The secreting tissues, whether spontaneously secreting or stimulated by histamine in the presence of burimamide, showed no significant changes over the period of exposure to the acid. The nonsecreting mucosae showed a progressive decrease in PD and Isc, ultimately becoming statistically significantly lower than the corresponding values for the spontaneously secreting mucosae. There was no significant change in the resistance of either group. TABLE 1. Effect 01 passing an electrical current (510 pa per em') from S ~ N for 30 min with secretory ph 6.0 (mean ± SEM)" Group PD(mv) R (ohmo em') Ise ("a/em ') Net H + output (,.Eq/em'!hr) I Spontaneous secretion (n = 11) Initial ± S ± ±8 4.0 ± 0.3 Final ± ± 20 78±S 2.9 ±0.3 P < P < P < P < n Secretion inhibited (n z 8) Initial ± ± ± 7 0 Final -2S.3 ± l.s 557 ± ± 8 0 NS NS NS TABLE 2. Effect of passing an electrical current (510 pq per em') from S ~ N for 30 min with secretory ph 2.25 (mean ± SE!.!)" Group PD(mv) R (ohms em') Ise ("a/em ') Net H'+" output (,.Eq/em'!hr) III Spontaneous secretion (n = 14) Initial -23.S ± ± 10 8O± ± 0.3 Final ± ± 7 61 ± ± 0.2 P < NS'" P < P < IV Secretion inhibited (n z 10) Initial ± ± 55 5O± ± 0.3 Final -3.4 ± ± ± ± O.S V Burimamide + histamine (n = 5) P < P < P < P < Initial ± ± 37 5O± ± 0.4 Final ± ± ± ± 0.7 P < NS- P < NS" "Values were recorded before passage of current (initial) and 30 min after cessation of current (final). P represents the significance of differences between initial and final values. NS, not significantly different.

4 Nouember 1976 TOLERANCE TO BACK DIFFUSION PO. 20 IIV C / I t 1til ICIM:I,1ctH O ~ 6 PMnfiol ""'--wi'" S«rriNy ph 2. ~ 10 - ~.. 8 _ -. --a.. lmoondt tmibilod Bu'lmOmidt ~ H i a f o m l n e.'7 pco.os o nne(ml.., FIG. 1. Effect on potential difference (PO) of exposure of the secretory surface to a solution of ph 2.25 for 3 Y. hr. Asterisk represents values that are significantly different from the corresponding value for the spontaneously secreting mucosae. 100 CIIongn in Shtlrl Ciralil Cu""".111 SM:rf1Qry ph 2.Z$ J.!.i!f <*', p <. O~ i,, ,'-,,,,l - -t, to _ f '. -SponlantGUI oterollo. L I 20 _. _. BurimGmid. inhibition '."r "-"'I ----aunmomldt -+-H,stoml o TIME (mini) FIG. 2. Effect on short circuit current (Iscl of exposure of the secretory surface to a solution of ph 2.25 for 3 y, hr. Asterisk represents values that are significantly different from the corresponding value for the spontaneously secreting mucosae c in O«:lnCtll ~ R,sislOfU willi Stt;"""y ph2.25 1lHS2.25 l!_. -1'-"'-._.. +_ "-1-' _ J --1=- i j ch i /, t - - ~ --5ponjonlOUl MCl',Iion - - -ilurimomicle inhibition ---8urimomlClt + HillOmln, o TIME/mins) FIG. 3. Effect on electrical resistance (R) of exposure of the secretory surface to a solution of ph 2.25 for :p;, hr. Taurocholate-induced back diffusion of H+. The changes in the electrical measurements and net H+ output of secreting and nonsecreting mucosae after 30 Illin of exposure to 10 mm sodium taurocholate at ph 2.25 (table 3) were almost identical to those achieved by the passage of current across equivalent groups of tissues. The secreting mucosae showed a significant decrease in the PD, but changes in Rand Isc were not significant. Highly significant depression of the PD, R, and Isc occurred in inhibited tissues, significantly greater than those of the spontaneously secreting mucosae (P < 0.001). Both groups showed a highly significant decrease of similar magnitude in the net H+ output (actual back diffusion). Intracellular ph. Table 4 shows the values for intracellular ph of fundic mucosae that were spontaneously secreting, stimulated by histamine, or inhibited by metiamide, and for antral mucosae. As intracellular ph, in part, reflects extracellular ph, U the difference between these two values may more accurately reflect the influence of the stimulation or inhibition of acid secretion. Comparison of these differences showed that stimulated tissues had a significantly more alkaline intracellular ph than the inhibited mucosae (P < 0.005). The difference between intracellular ph and extracellular ph of the inhibited tissues was identical to the difference for antral mucosae. Discussion In these experiments, back diffusion was induced by passing an electrical current across the mucosa thereby driving protons from an acid secretory fluid into the tissue, by establishing a large concentration gradient for H+ from the secretory fluid into the tissue, or by adding sodium taurocholate to an acid secretory fluid. The latter two methods have been previously established as techniques for inducing back diffusion of H Externally applied current has previously been used in studies of the gastric acid secretory mechanism, albeit not for the specific purpose of induction of back diffusion of H +. Each of these studies noted that, after application of current (2 to 4 rna per cm ') from S to N of the secreting mucosa, there was a prolonged depression of the PD and the acid secretory rate, an effect not seen after current flow in the reverse direction. Rehm 11 found the changes to be strikingly similar to those after application of HCI (ph 0.64 to 1.03) to the mucosa of the secreting stomach,li and proposed u that the effect was due to retrograde transport of H+ into the mucosal cells. Using a CI--containing secretory fluid, Rehm was unable to account for all of the current flow in terms of H+ and Cl- movement and postulated that passage of the current was associated with movement of other ions also. However, Forte, 10 using a chloride-free secretory fluid to prevent unidirectional back flux of Cl- from S -> N, has shown that almost all of the current flowing through the mucosa is accounted for by the net changes in H + and CI- movement. The actual rate of back diffusion of H+ that was induced by the passage of the current in our experiments is not known. Because of technical limitations of the ph stat system, especially the significant influence of minor changes in room temperature on the response of the ph electrode at ph 2.25, separation of the current-induced

5 764 O'BRIEN AND SILEN Vol. 71. No.5 "TABLE 3. Effect of 10 mm.odium taurocholate in secretory solution for 30 min with secretory ph 2.25 (mean = SEM)" Group PO (mv) R(ohmscm') Isc (pa/cm') Net H + output ("Eq/cm '/h,) Spontaneous secretion (n - 7) Initial = = = =0.6 Final -17.4= = 26 66=8-1.1 = 0.9 P <0.05 NS NS P < 0.01 Secretion inhibited (n _ 5) Initial -29.S = = = ± 0.5 Final -S.4 = = 24 25= = 0.7 P <0.001 P < P < P < " Values were recorded before exposure (initial) and 30 min after removal of the taurocholate solution (final). P represents the significance of differences between initial and final values. NS, not significantly different. TABLE 4. Intracellular ph of amphibian fundic and antra/gastric mucosa" Fundic mu80ca Intracellular ph Extracellular ph Difference Spontaneous secretion 7.23 = = ± 0.03 (n = 12) Histamine stimulation 7.28 = = = 0.03 (n - 11) Metiamide inhibition 7.11 = S ± =0.02 (n.lo) Antral mucosa 7.17 ± = =0.03 (n _ 10) Values represent mean = SEM. This value differs significantly from the corresponding value (difference in extracellular and intracellular ph) for the spontaneously secreting mucosa (P < 0.05) and from the metiamide inhibited mucosa (P < 0.005). H+ movement from the existing net H+ movement was not possible. However, an estimate of the expected rate of back diffusion of H+ that would be induced by a current of 510 #,a per cm '(19 #'Eq per cm 2 per hr) may be derived. H+ and CI- are the primary constituents of the bathing solutions that carry the current.1o Assuming equal permeability of the mucosa to both ions, the contribution of each ion would be in proportion to its concentration and thus the current would induce movement of approximately 18 #'Eq per cm' per hr of CI- and 1 #'Eq per cm' per hr of H+. The conductance of the secretory membrane to H+ at secretory ph 2.25 is almost certainly less than the CI- 'conductance, II and thus induced back diffusion of H+ would probably be somewhat less than 1 #'Eq per cm t per hr. It would be desirable to ascertain whether the amount of back diffusion of H+ induced into the secreting and nonsecreting mucosae were comparable. Although accurate direct measurement of the actual amount of back diffusion of H+ was not possible for reasons mentioned above, theoretical considerations suggest that the nonsecreting mucosae were not subjected to greater induced back diffusion than were the secreting tissues. In both groups, the electrochemical gradients were identical. The rate of back diffusion induced thus depended on the permeability of the tissues to H+. Because burimamide causes an increase in the electrical resistance, it seems reasonable to assume that permeability to H+ would be reduced. If anything, this alteration would lower the back diffusion in the inhibited tissues, those most injured by H+ back diffusion. The back-diffusing H+ would be expected to pass transcellularly rather than intercellularly. Studies of the effects of an acidified nutrient environment lo U indicate that the resistance of the extracellular leak pathway is high relative to that via the cell. Conductance through the surface epithelial cells of the amphibian gastric mucosa is approximately 4 times greater than through the intercellular pathway.u We have shown that induction of back diffusion ofh+ into the nonsecreting gastric mucosa results in marked depression of the PD, R, and Isc, indicating severe compromise of active transport processes and increased permeability. The results were remarkably similar whether H+ back diffusion was induced by current, by concentration gradient, or by topical application of sodium taurocholate. Active brisk secretion appears to be associated with an increased tolerance of the mucosa to these manipulations. It appears unlikely that the acid secretory inhibitor, burimamide, is itself responsible for the observed impaired tolerance to H+. Stimulation of secretion with histamine in the presence of burimamide prevented the marked depression of the electrical parameters encountered after passage of current across inhibited tissue. During secretion, for each H+ and OH- is formed, which is neutralized by COt and passed into the nutrient fluid as HCO, In the actively secreting mucosa in vitro, base production exceeds the endogenous supply of CO, so that COt is taken up by the cell. 21 Measurements of the arteriovenous changes in HCO. - concentration and Pco, in the ex vivo canine stomach" and the gastric fistula cat" confirm these findings in the perfused stomach. The base formed during H+ secretion would be expected to alkalinize the intracellular environment before passing across the nutrient membrane as HCO, -. Our finding, that the intracellular ph of the histaminestimulated mucosa is significantly more alkaline than that of the metiamide-inhibited mucosa, supports this concept. The decresed Pco, and elevated HCO. - concentration, derived from acid secretory activity, would therefore provide a favorable intracellular and nutrient environment for the neutralization of back-diffusing H+. The gastric mucosal barrier has been defined classically by the measurement of the absolute quantity of H-+

6 November 1976 TOLERANCE TO BACK DIFFUSION 765 that leaves the lumen in a given unit of time. In view of the experiments reported herein, such a description of the barrier seems excessively restrictive and omits the dimension of the capacity of the mucosa to resist H+. Thus, two mucosae may be exposed to equal quantities of H+ with marked anatomical and physiological alterations in one in which secretion is inhibited, whereas the other may be completely unaltered. The concept of the gastric mucosal barrier should probably no longer describe the barrier as a static gate but rather as a dynamic and functionally changeable capacity of the mucosa. Because the capacity of the mucosa to tolerate H + is dependent on the functional state of the tissue, the measure of the absolute loss of H + from the mucosal solution is probably not an adequate assessment of the gastric mucosal barrier. REFERENCES 1. Davenport HW: Back diffusion of acid through the gastric mucosa and its physiological consequences. In Progress in Gastroenterology, vol 2. Edited by G Jerzy-Glass. New York, Grune & Stratton, 1970, p Moody FG, Aldrete JS: Hydrogen permeability of canine gastric epithelium during formation of acute superficial erosions. Surgery 70: , Cheung LY, Moody FG, Torma MJ, et al: Direct effects of endotoxin on canine gastric mucosal permeability and histological changes. J Surg Res 18: , Ritchie WP: Ischemia and the gastric mucosal barrier: a note of caution. Surgery 76: , Silen W, Skillman JJ: Stress ulcer, acute erosive gastritis and the gastric mucosal barrier. In Advances in Internal Medicine, vol 19. Edited by GH Stollerman. Chicago, Year Hook Medical Publishers, 1974, p Menguy R, Desbaillets L, Masters YF: Mechanism of stress ulcer. 1. Influence of hypovolemic shock on energy metabolism in the gastric mucosa. Gastroenterology 66:46-55, Wlodek GK, Leach RK: The effect of histamine stimulation on the net ionic fluxes in Heidenhain and Pavlov fundic pouches. Can J Surg 10:47-52, Altamirano M: Back diffusion of H + during gastric secretion. Am J Physiol 218:1-6, Moody FG, Davis WL: Hydrogen and sodium permeation of canine gastric mucosa during histamine and sodium thiocyanate administration. Gastroenterology 59: , Sanders SS, Hayne Van B Jr, Rehm WS: Normal H+ rates in frog stomach in absence of exogenous CO. and a note on ph stat method. Am J Physiol 225: , Bray GA: A simple efficient liquid scintillator for counting aqueous solutions in a liquid scintillation counter. Anal Biochem 1: , Herberg RJ: Statistical aspects of double isotope liquid scintillation counting by internal standard technique. Anal Chem 36: , Butler TC: Quantitative studies of the demethylation of trimethadione (Tridione). J Pharmacol Exp Ther 108:11-17, Waddell WJ, Butler TC: Calculation of intracellular ph from the distribution of 5,5-dimethyl-2,4-oxazolidinedione (DMO). Application to skeletal muscle of the dog. J Clin Invest 38: , Waddell WJ, Bates RG: Intracellular ph. Physiol Rev 49: , Teorell T: On the permeability of the stomach mucosa for acids and some other substances. J Gen Physiol 23: , Davenport HW: Destruction of the gastric mucosal barrier by detergents and urea. Gastroenterology 54: , Rehm WS: The effect of electric current on gastric secretion and potentia\. Am J Physiol 144: , Crane EE, Davies RE, Longmuir NM: The effect of electric current on HCl secretion by isolated frog gastric mucosa. Biochem J 43: , Forte JG: Hydrochloric acid secretion by the gastric mucosa. In Membranes and Ion Transport, vol. 3. Edited by E Bittar. New York, John Wiley & Sons, 1970, p Rehm WS: The effect of histamine and Hel on gastric secretion and potential. Am J PhysioI141: , Rehm WS: Effect of electric current on gastric hydrogen ion and chloride ion secretion. Am J Physiol 185: , Harris JB, Edelman IS: Chemical concentration gradients and electrical properties of gastric mucosa. Am J Physiol 206: , Silen W, Machen TE, Forte JG: Acid-base balance in amphibian gastric mucosa. Am J Physiol 229: , Spenney JG, Shoemaker RL, Sachs G: Microelectrode studies of fundic gastric mucosa: cellular coupling and shunt conductance. J Membrane BioI 19: , Davies RE: Hydrochloric acid production by isolated gastric mucosa. Biochem J 42: , Teorell T: The acid-base balance of the secreting isolated gastric mucosa. J Physiol 114: , Russell JG, Kowalewski K: The acid-base balance in gastric H+ secretion. Physiol Chem Physics 6: , A1hinus M, Sewing K-Fr: Acid base balance in relation to gastric acid secretion stimulated by histamine and pentagastrin in cats. Naunyn Schmiedebergs Arch Pharmacol 285: , 1974