Effects of verapamil on the contractions of guinea-pig

Transcription

1 Br. J. Phrmc. (1985), 84, Effects of verpmil on the contrctions of guine-pig trchel muscle induced by C, Sr nd B K. Bb, M. Kwnishi*, T. Stke & T. Tomit** The 2nd Deprtment of Internl Medicine, Deprtment of Anesthesiology* nd Deprtment of Physiology**, School of Medicine, Ngoy University, Ngoy 466, Jpn 1 A comprison ws mde of contrctions produced by clcium (C), strontium (Sr) or brium (B) in guine-pig trchel smooth muscle fter the preprtion hd been relxed in C-free medium. Most of the experiments were crried out in the presence of indomethcin (5 JAM) to inhibit endogenous prostglndin synthesis. In 40 mm K+ solution, the C, Sr nd B concentrtions which produced 50% of mximum tension responses were 0.07 mm, 1 mm nd 2 mm, respectively. Mximum tension of similr size ws produced by either 2.4 mm C, 9.6 mm Sr or 9.6 mm B. 2 The C-induced contrction in 5.9 mm K solution, which is probbly due to the presence of endogenous prostglndins, ws not significntly ffected by verpmil. When the externl K concentrtion ws incresed to 40 mm, the C-induced contrction becme susceptible to inhibition by verpmil. Similrly, contrctions induced by Sr nd B in excess K solution were strongly suppressed by verpmil. 3 In the presence of prostglndin (PG) F2 (1.4 l4m) or crbchol (5 ylm), C, Sr nd B produced contrctions in both the 5.9 mm K nd 40 mm K solutions. Contrctions produced by PGF2C, or crbchol in the presence of C were little ffected by 10 tam verpmil, wheres those in the presence of Sr or B were strongly suppressed by verpmil in both the 5.9 nd 40 mm K solutions. 4 A strong suppressnt effect of verpmil on the K-induced contrction, but wek effect on the drug-induced contrction, in the presence of C cn be explined by ssuming tht verpmil blocks voltge-operted C chnnels, but not receptor-operted C chnnels. However, this theory cnnot ccount for the effect of verpmil on drug-induced contrctions in the presence of Sr or B. It my be tht susceptibility to verpmil is determined by the reltive ffinity of'the divlent ctions nd verpmil for the C chnnels, both for voltge- nd receptor-operted chnnels. Introduction It is generlly ssumed tht clcium ion (C2+) influx from the extrcellulr medium is minly responsible for contrction of smooth muscle s, in most smooth muscles, contrctions re quickly reduced or bolished by removl of externl clcium or dministrtion of 'clcium ntgonists'; inhibitions which re scribed to reduction in the trnsmembrne influx of clcium ions (Fleckenstein, 1983). However, in some smooth muscles, for exmple some vsculr or irwys smooth muscles, the removl of externl C2' does not bolish the contrction induced by stimulting gents s rpidly s it prevents the contrction induced by incresing the externl K+ concentrtion (Hudgins & Weiss, 1968; Kirkptrick et l., 1975; Ito et l., 1977; for review see Bolton, 1979). Furthermore, 'clcium ntgonists' such s verpmil or D-6000 (methoxyverpmil) hve little effect on the contrctions induced by gonists t cholinoceptors or drenoceptors, lthough they suppress high K+-induced contrctions (Golenhofen & Hermstein, 1975; Coburn, 1977; Golenhofen, 1981; Meisheri et l., 1981). This could be due to the fct tht, in these muscles, the contrctions induced by the gonists re dependent on intrcellulr C2+ relese (Kuriym, 1981), nd/or on influx of C2+ through receptor-operted C chnnels, which re different from the voltge-operted chnnels ctivted by depolriztion of the membrne by excess K+ (Bolton, 1979). The guine-pig trchel smooth muscle exhibits spontneous tone in norml Krebs solution tht is probbly mintined by prostglndins synthesized by the trchel muscle itself (Orehek et l., 1975). Although this tone is redily blocked in clcium-free C) The Mcmilln Press Ltd 1985

2 204 K. BABA etl. solution, it is little ffected by verpmil t concentrtion up to 10-5 M (Duncn & Dougls, 1984; Kwnishi et l., 1984). In irwys smooth muscle, contrctions induced by cetylcholine or prostglndins re considered to be much less sensitive to clcium ntgonists thn those in other types of smooth muscle (Coburn, 1977; Himori & Tir, 1980; Triggle, 1983). In the present studies, the effects of verpmil on the contrction induced by either crbchol or prostglndin F2 (PGF2,) were further investigted in the guine-pig trchel muscle under conditions in which clcium ws substituted by strontium (Sr) or brium (B). It is known tht Sr2+ nd B2+ cn produce ction potentils nd contrctions in severl types of smooth muscles, probbly by crrying the inwrd current through the C chnnel (Bfilbring & Tomit, 1969; Kuriym & Tomit, 1970; Skmoto, 1970; 1971; Uvelius etl., 1974; Tkt, 1979; Hott & Ymmoto, 1983). It ws hoped tht the combintion of the effects of clcium ntgonist nd substitution of C2+ with other divlent ctions might be useful pproch to clrify the role of clcium pthwys in trchel smooth muscle contrction. Methods Guine-pigs weighing g were stunned nd bled, nd the trche removed. The muscle strip contined in one crtilge ring ws crefully dissected out with the short crtilge ttched ech side of the muscle strip, nd it ws fixed verticlly in n orgn bth (1 ml volume) for the recording of isometric tension. The preprtion ws superfused with test solutions t constnt rte (1.5 ml min-1). After equilibrting the preprtion in norml bthing solution for 30 min, isoprenline (2 ILM) ws pplied to produce complete relxtion. Under these conditions the tension ws djusted to 250 mg by stretching the preprtion nd the isoprenline ws wshed out. The experiment ws strted fter the resting tension hd developed gin nd hd reched n pproximtely constnt level. The norml bthing solution hd the following composition (mm): NCl 137, KHCO3 5.9, CCl2 2.4, MgCl2 1.2 nd glucose 11.8, erted with 99% 02 nd 1 % CO2. When C2+ ws substituted by Sr2+ or B2, their concentrtion ws usully 9.6 mm, 2.4 mm CCl2 nd 10.8 mm NCl were replced with the divlent ction to mintin the osmolrity of the solution. EGTA (ethyleneglycol-bis-(p-minoethylether) N,N'-tetrcetic cid) 0.5 mm ws lwys dded to 'C-free' solution, except in the experiments where the concentrtion-response reltionship of divlent ctions ws studied. All experiments were crried out t 35 C. The drugs used were indomethcin, isoprenline, crbchol, EGTA nd prostglndin (PG) F2M. All drugs were obtined from Sigm, except PGF2o (Ono Phrmceuticl Co.) nd verpmil (Knoll A.G.). Contmintion by clcium, of the C-free solutions, ws less thn 1 tlm when mesured by tomic bsorption spectroscopy. Results The concentrtion-response reltionship for C2+ ion ws compred with those for Sr2+ nd B2+ ions. In these experiments, the preprtions were first exposed to C-free 40 mm K' solution contining indomethcin (5 tim) nd then C ws pplied cumultively from to 9.6mM to produce stedy stte of contrction t ech concentrtion. Indomethcin ws dded in ll of these experiments, but the results were essentilly the sme s those obtined when indomethcin ws not present. Similrly, Sr nd B were pplied to the sme preprtion in this order t intervls of 30 min; the results re summrized in Figure 1. The threshold concentrtion for C ws much lower thn tht for Sr nd B. The concentrtion-response curves were similr for Sr nd B. The concentrtion which produced 50% of mximum tension ws bout 0.07 mm for C, 1 mm for Sr nd 2 mm for B. In some experiments, concentrtion-response curves were obtined using seprte preprtions for ech divlent ction but no significnt difference ws found 0-0 c ) Ion concentrtion (mm) Figure 1 Concentrtion-response reltionships of C (-), Sr (A) nd B (U) in C-free, 40 mm K+ solution contining indomethcin (5 Mm) in guine-pig trchel muscle. The divlent ctions were pplied cumultively to the sme preprtion in the order C, Sr nd B t intervls of 30 min, for t lest 20 min, by which time stedy stte of contrction hd been reched. Ordinte: percentge of the mximum tension for ech divlent ction; ech point shows the men (n= 4) nd verticl lines s.d.

3 VERAPAMIL ON CONTRACTURE INDUCED BY CA, SR OR BA X\ /'\ 05 g C 2.4 mm Sr 9.6 mm C 2.4 mm Sr 9.6 mm 30 min b C 2.4 mm B 9.6 mm C 2.4 mm B 9.6 mm 30 min Figure 2 Contrctions produced by repeted ppliction of 9.6 mm Sr () nd 9.6 mm B (b). The preprtions were first exposed to C-free 40 mm K+ solution contining 0.5 mm EGTA nd 5 AM indomethcin, nd control responses to C (2.4 mm) were observed twice. The trce strted from the second response to C. EGTA ws present throughout, except for 10 min before nd throughout ech C ppliction. Note the nerly constnt responses to Sr but slow decrese in B responses nd lso tht C tretment did not ffect subsequent Sr responses (), but potentited subsequent B responses (b). from those shown in Figure 1. Thus, tretment with one divlent ction did not ffect the tension development in the presence of other ctions if the intervl between pplictions ws bout 30 min. Mximum tension ws produced by pproximtely 2.4mM C, 9.6mM Sr nd 9.6mM B, nd their bsolute vlues were 0.73 ± 0.02 g for C, 0.64 ± 0.07 g for Sr nd 0.80 ± 0.20 g for B (men ± s.d., n = 4). When expressed reltive to tht for C, the vlues were 86.6 ± 8.2% for Sr nd 108 ± 26.2% for B. 100 C In Figure 2, Sr () nd B (b) were repetedly pplied to C-free 40mM K+ solution (contining 0.5 mm EGTA) for 20 min t 25 min intervls fter observing control response to the reddition of C2+. The mximum tension induced by Sr (9.6 mm) ws smller thn tht induced by C (2.4 mm), but it remined nerly constnt during the successive pplictions of Sr, nd ws not significntly ffected by interposing C-induced contrction between the Sr-induced responses. The tension induced by B (9.6 mm) decresed grdully nd linerly on succesb Sr c B J so 8 7Ver 10 8 p 7 10(6 M) lo5 Verpmil (M) Figure 3 Effects of verpmil on the contrctions induced by 2.4 mm C (), 9.6 mm Sr (b) nd 9.6 mm B (c) in 40 mm K+ solution contining indomethcin (5 gm). EGTA (0.5 mm) ws dded to Sr nd B solutions. Different preprtions were used for ech concentrtion-response curve nd the mximum responses before the ddition of verpmil were tken s 100%. Ech point is the men of 4 different preprtions nd verticl lines represent the s.d.

4 206 K. BABA etl. sive pplictions of this ion, nd the 4th response ws bout 75% of the 1st response. When C ws dded fter the 4th response to B, the tension produced ws much smller thn the control response to C but this tretment resulted in prtil recovery of the subsequent B response. The rte of relxtion on removl of the divlent ctions ws fster for C nd Sr thn for B nd it becme grdully slower when B ws repetedly pplied. Effects of verpmil on the contrctions produced by C (2.4 mm), Sr (9.6 mm) nd B (9.6 m) were compred nd the results shown in Figure 3. Verpmil hd little effect on C-induced contrction in 5.9 mm K+ solution, wheres it suppressed Cinduced contrctions significntly in 40 mm K+ solution (Figure 3), s shown previously (Kwnishi et l., 1984). The contrctions induced by Sr nd B were similrly suppressed by verpmil in 40 mm K+ medium. There ws no cler difference in the effect of verpmil on the contrctions induced by the three divlent ctions. In Figure 4, the contrctions induced by the different divlent ctions were compred in the presence of o - 0._n _ Ion concentrtion (mm) Figure 4 Concentrtion-response curves for C (-), B (U) nd Sr (A) in the presence of () prostglndin (PG)F2, (1.4 tim) nd (b) crbchol (5 jlm). Experimentl procedure ws the sme s Figure 1 nd C, Sr nd B were pplied in this order without EGTA. The mximum responses to 2.4 mm C, 9.6 mm B nd 19.2 mm Sr were tken s 100%. Ech point represents the men of 4 different preprtions nd verticl lines indicte s.d. E PGF2 (1.4 mm) or crbchol (5 ALM). In these experiments, the preprtions were first exposed to C-free solution, nd PGF2, (1.4 f±m) or crbchol (5 tim) ws dded. No cler contrction ws observed when these two gonists were dded 15 min fter the removl of C. These experiments were lso crried out in the presence of indomethcin (5 ytm) to bolish the bsl tone. The concentrtion-response curves in the presence of PGF2, were roughly prllel for ll three divlent ctions nd the sensitivity ws C > B > Sr. In the presence of crbchol, the concentrtion-response curves for C nd B were shifted to left nd the curves were steeper compred Cotrl Verpmil < 0 I- ) 100, PGF2,x (M). 1 b T Control Verpmil 50* T I l Crbchol (M) Fgure 5 Effects of verpmil on the responses to prostglndin (PG) F24 () nd crbchol (b) in norml bthing solution contining 2.4 mm C nd 5 JIM indomethcin. Ordintes: tension expressed s percentge of the response to 2.8 lim PGFU nd 0.1 mm crbchol, before the ddition of verpmil. Abscisse: concentrtions of PGFU () or crbchol (b). After monitoring the control response twice t 30 min intervl, verpmil (10 glm) ws dded nd 30 min lter concentrtion-response curve ws gin obtined. Ech point represents the men of 4 preprtions nd verticl lines indicte s.d.= ;

5 VERAPAMIL ON CONTRACTURE INDUCED BY CA, SR OR BA 207 C I b Sr c B PG F2 d C Il e Sr Ilf B Pr,l: * iczq 30 min Figure 6 Comprison of responses to prostglndin (PG) F2 (1.4 pm) in the presence of C (2.4mm), Sr (9.6 mm) nd B (9.6 mm), nd effects of verpmil (10-5M) on these responses. The preprtion ws first treted with C-free solution contining 5.9 mm K, 5 Am indomethcin nd 0.5 mm EGTA. EGTA ws removed 10 min before nd throughout C ppliction. ( to f) Successive responses t 40 min intervls obtined from the sme preprtion, nd (d to f) responses in the presence of verpmil (10 Am). j with those in the presence of PGFu. The contrctions produced by Sr in the presence of PGFu were not so mrkedly different from those produced in the presence of crbchol. The concentrtion which resulted in 50% mximum tension ws 0.24 mm for C, 1.5 mm for B nd 4.4 mm for Sr in the presence of PGFu, nd 0.1 mm for C, 0.9 mm for B nd 5.6 mm for Sr in the presence of crbchol. Thus, the reltive sensitivity to different divlent ctions ws not so gretly different between PGF,, nd crbchol. The contrctions produced by cumultive dministrtion of PGF,. (3 nm-3 tlm) or crbchol (30 nm-0.1 mm) were compred in solutions contining 2.4mM C nd 51tM indomethcin, in the presence nd in the bsence of verpmil (10 tm) (Figure 5). Verpmil hd no depressnt effect on contrctions induced by PGF,1 except t very high concentrtions (0.8-3 ltm) (Figure 5), wheres the contrctions produced by low concentrtions (less thn 1 llm) of crbchol were very mrkedly suppressed by verpmil. As the concentrtion of crbchol ws incresed, however, the suppression becme less significnt nd the effect disppered t 0.1 mm crbchol (Figure Sb). It hs lso been found tht verpmil (up to 131 JuM) hs little effect on the histmine (50 pm)-induced contrction (Duncn & Dougls, 1984). In the experiment shown in Figure 6, the preprtion ws first relxed by exposing it to C-free Krebs solution contining indomethcin (5 AM) nd EGTA (0.5 mm), then either C (2.4 mm), Sr (9.6 mm) or B (9.6 m) ws pplied (in this order) for 40 min. In the presence of indomethcin C produced no response (Figure 6), Sr wek contrction (Figure 6b), nd B strong contrction (Figure 6c). This suggests tht the contribution of prostglndins is lrger to C- or Sr-induced contrctions thn to B-induced contrctions. However, the underlying mechnism for the contrctions induced by Sr nd B ws not investigted in the present experiment. Addition of PGFu (1.4I1M) produced contrctions in the presence of these divlent ctions, s expected from Figure 4. In the presence of verpmil (10 jam) the sme type of experiments ws crried out. The contrction induced by PGFu in the presence of C ws only slightly reduced by verpmil (Figure 6d). On the other hnd, verpmil strongly suppressed not only the contrctions induced by either Sr or B, but lso those produced by PGFu in the presence of these two ions (Figure 6e,f).

6 1~~~~~~~~~~~~~ j 208 K. BABA etl. C b Sr c B PG F2 Verpmil d C e Sr f B PGF2t 30 min Figure 7 The sme type of experiment s Figure 6, but the responses to prostglndin (PG) F2CK (1.4 lm) in the presence of C (2.4 mm), Sr (9.6 mm) nd B (9.6 mm), nd the effects of verpmil (d-f) on these responses, were compred in C-free solution contining 40 mm K+ (cf 5.9 mm K+ in Figure 6), 5 JlM indomethcin nd 0.5 mm EGTA. C b Sr c B Crbchol Verpmil d C e Sr f B.1~ ~ ~ ~ Crbchol 30 min igure 8 The sme type of experiment s Figure 6 but the responses to crbchol (5 jam) (cf. prostglndin F2CK) were compred in the presence of C (2.4 mm), Sr (9.6 mm) nd B (9.6 mm) nd the effects of 10-5 M verpmil (d-f) on these responses. The bthing solution contined 5.9 mm K+, 5 JAM indomethcin nd 0.5 mm EGTA.

7 VERAPAMIL ON CONTRACTURE INDUCED BY CA, SR OR BA 209 C b r Sr i c B Crbchol Verpmil d C 1-- e Sr f B C c Crbchol I 30 min Figure 9 The sme type of experiment s Figure 8 but responses to crbchol (5 LM) in the presence of C (2.4 mm), Sr (9.6 mm)) nd B (9.6 mm), nd the effects of 10-5M verpmil (d-f) on these responses, were compred in C-free solution contining 40 mm K+ (cf. 5.9 mm K+), 5 jim indomethcin nd 0.5 mm EGTA. The sme type of experiment s tht shown in Figure 6 ws repeted in 40 mm K+ medium (Figure 7). Under these conditions, C, Sr nd B ll produced contrctions of similr size in the presence of indomethcin. Thus, the min difference between the response ptterns in norml nd excess K+ medi ws found in the response to C nd Sr. Addition of PGFu further incresed the tension produced by the divlent ctions. Verpmil suppressed only the response induced by C itself, the contrction to PGF2. in the presence of C being little ffected, s in 5.9mM K+ medium (Figure 7d). However, s in 5.9 mm K+ medium, verpmil suppressed not only the contrctions produced by Sr nd B but lso those by PGFu in the presence of Sr nd B (Figure 7e,f). The effects of verpmil on the responses to crbchol (5 pm) were essentily the sme, both in norml (5.9 mm) K+ (Figure 8) nd in excess (40 mm) K+ (Figure 9), s those on the responses to PGFu. The responses to crbchol in the presence of C were resistnt (Figures 8d nd 9d), while those in the presence of Sr nd B were very susceptible, to verpmil (e,f, in Figures 8 nd 9). Discussion In the guine-pig trchel muscle, Sr nd B re less effective in producing contrction thn C. An pproximtely 20 times higher concentrtion of Sr or B ws necessry to produce 50% mximum tension nd bout 4 times higher for mximum tension development. However, the reltive tension induced by these divlent ctions in the depolrized condition in excess (40 mm) K+ solution ws similr, being 1:0.9:1.1 for C, Sr nd B, respectively. It is difficult to explin the underlying mechnism of ctivtion of the contrctile elements by Sr nd B. According to n experiment on the chicken gizzrd, sensitivity of myosin B to Sr nd B is 1/20 nd 1/210, respectively, in comprison to C (Ebshi & Endo, 1968). If this reltionship cn lso be pplied to the trchel muscle, one must ssume tht Sr nd B re much more perment ions thn C nd/or tht Sr nd B relese intrcellulr C. In other smooth muscles, such s guine-pig vs deferens (Jurkiewicz et l., 1975), ileum (Antonio et l., 1973) nd teni coli (Krki et l., 1967), the

8 210 K. BABA etl. contrction produced by B grdully disppers in C-free solution, but it recovers fter short tretment with C. In these experiments, the contrctions re interpreted s being due to C relese from n intrcellulr store by B. On the other hnd, in the rt portl vein (Uvelius et l., 1974), nd the rt ileum (Tniym etl., 1977), it hs been shown tht Sr nd B cn still produce significnt contrction in depolrized preprtion exposed for more thn 2 h to C-free solution contining EGTA, observtions which suggest tht the contrctile mchinery cn, t lest prtly, be directly ctivted by these divlent ctions. In the present experiments on trchel muscle, the Sr-induced contrcture remined nerly constnt for 3 h, nd this ws not ffected by the reddition of C. This result cnnot be explined by Srinduced intrcellulr C relese. The response to B slowly decresed in C-free solution but the reduction ws only 25% in 3 h nd the contrction produced by C ws lso similrly reduced fter the B tretment. This suggests tht the reduction of the B-induced contrcture is not due to depletion of intrcellulr C but due to some deleterious effect of B which is probbly relted to slowing of the relxtion. Since crbchol nd PGF2u do not produce contrctions in C-free solution, influx of C (or other divlent contrctile ctions) is considered to be essentil for the production of response to these gonists. Thus, in the guine-pig trchel muscle, it is most likely tht Sr nd B re ble to ctivte directly the contrctile protein with n efficiency similr to C, lthough C relese from some intrcellulr store cnnot be completely ruled out. In some smooth muscles, it is known tht verpmil more redily blocks K+-induced contrctions thn drug-induced contrctions (Coburn, 1977; Bolton, 1979; Golenhofen, 1981). When drug-induced contrction is resistnt to removl of externl C, the contrction is likely to be cused by intrcellulr C relese. However, there re some smooth muscles in which the drug-induced contrction is esily inhibited by C removl, lthough it is resistnt to verpmil (Golenhofen, 1981). Such contrction is probbly due to C influx through some pthwy which is not ffected by verpmil. This supports the ide tht two different C pthwys exist; i.e., voltge-operted nd receptor-operted C chnnels which hve different ffinities for verpmil (Bolton, 1979). The C-induced contrction in the presence of crbchol or PGF2,, is lso very resistnt to verpmil in the guine-pig trchel muscle. If the verpmil sensitivity is relted to the difference between voltge-dependent nd receptor-operted C chnnels, one would expect tht the contrctions induced by drugs in the presence of Sr or B would be similrly resistnt to verpmil blockde but they re esily bolished by verpmil. This result suggests tht the susceptibility of the C2+ chnnel to C ntgonists does not depend on the type of C chnnel involved. It my be rgued tht Sr nd B utilize the voltgeoperted C chnnel even when the contrction is induced by drugs. However, since the mximum K- induced contrcture in the presence of Sr or B cn be still further incresed by the ddition of prostglndin F2u or crbchol, the C pthwy opened by drugs seems to be different from the voltgeoperted C chnnel, similrly for Sr nd B. Another possibility is tht in the presence of Sr or B, the contribution of the voltge-operted chnnel to the drug-induced contrction my be reltively lrger thn in the presence of C. However, this does not explin the nerly complete inhibition of druginduced contrctions by verpmil in the presence of Sr or B. Our tenttive hypothesis is tht the ffinity of the C chnnel, both voltge-operted nd receptoroperted, to different ctions nd to verpmil vries depending on the experimentl conditions nd tht the intensity of the blocking ction of verpmil is determined by the reltive ffinity of verpmil nd the ctions for the chnnel. In the depolrized condition, verpmil hs stronger ffinity for the chnnel thn the divlent ctions, while in the presence of the two gonists studied C hs stronger ffinity thn verpmil but Sr nd B hve weker ffinity thn verpmil. However, more direct evidence is necessry to dvnce this hypothesis. We re grteful to Professor R.F. Coburn, University of Pennsylvni, for improving the mnuscript. References ANTONIO, A., ROCHA E SILVA, M. & YASHUDA, Y. (1973). The tchyphylctic effect of brium on intestinl smooth muscle. Arch. int. Phrmcodyn., 204, BOLTON, T.B. (1979). Mechnism of ction of trnsmitters nd other substnces on smooth muscle. Physiol. Rev., 59, BCJLBRING, E. & TOMITA, T. (1969). Effect of clcium, brium nd mngnese on the ction of drenline in the smooth muscle of the guine-pig teni coli. Proc. R. Soc. Lond. B., 172, COBURN, R.F. (1977). The irwy smooth muscle cell. Fedn. Proc., 36, DUNCAN, P.G. & DOUGLAS, J.S. (1984). Sensitivity nd

9 VERAPAMIL ON CONTRACTURE INDUCED BY CA, SR OR BA 211 responsiveness of trchel nd bronchil tissues from young nd old guine pigs: effect of clcium ntgonists. J. Phrmc. exp. Ther., 228, EBASHI, S. & ENDO, M. (1968). Clcium ion nd muscle contrction. Prog. Biophys. Molec. Biol., 18, FLECKENSTEIN, A. (1983). Clcium ntgonism, bsic principle of drug-induced smooth muscle relxtion. In Clcium ntgonism in Hert nd Smooth Muscle, ed. Fleckenstein, A., pp New York:John Wiley & Sons, Inc. GOLENHOFEN, K. (1981). Differentition of clcium ctivtion process in smooth muscle using selective ntgonists. In Smooth Muscle: An Assessment of Current Knowledge, ed. Bulbring, E., Brding, A.F., Jones, A.W. & Tomit, T., pp London:Edwrd Arnold. GOLENHOFEN, K. & HERMSTEIN, N. (1975). Differentition of clcium ctivtion mechnisms in vsculr smooth muscle by selective suppression with verpmil nd D 600. Blood Vessels, 12, HIMORI, A. & TAIRA, N. (1980). Differentil effects of the clcium-ntgonistic vsodiltors, nifedipine nd verpmil, on the trchel musculture nd vsculture of the dog. Br. J. Phrmc., 68, HOTTA, K. & YAMAMOTO, Y. (1983). Ionic mechnisms involved in the strontium-induced spike nd plteu in the smooth muscle of rt portl vein. J. Physiol., 336, HUDGINS, P.M. & WEISS, G.B. (1968). Differentil effects of clcium removl upon vsculr smooth muscle contrction induced by norepinephrine, histmine nd potssium. J. Phrmc. exp. Ther., 159, ITO, Y., SUZUKI, H. & KURIYAMA, H. (1977). On the roles of clcium ion during potssium induced contrcture in the smooth muscle cells of rbbit min pulmonry rtery. Jp. J. Physiol., 27, JURKIEWICZ, A., MARKUS, R.P. & PICARELLI, Z.P. (1975). Effect of full gonists following clcium deprivtion in rt vs deferens. Eur. J. Phrmc., 31, KARAKI, H., IKEDA, M. & URAKAWA, N. (1967). Effects of externl clcium nd some metbolic inhibitors on brium-induced tension chnges in guine pig teni coli. Jp. J. Phrmc., 17, KAWANISHI, M., BABA, K. & TOM1TA, T. (1984). Effects of N removl nd redmission on the mechnicl response in the guine-pig trchel smooth muscle. Jp. J. Physiol., 34, KIRKPATRICK, C.T., JENKINSON, H.A. & CAMERON, A.R. (1975). Interction between drugs nd potssium-rich solutions producing contrction in bovine trchel smooth muscle: studies in norml nd clcium depleted tissues. Clin. exp. Phrmc. Physiol., 2, KURIYAMA, H. (1981). Excittion-contrction coupling in vrious viscerl smooth muscles. In Smooth Muscle: An Assessment of Current Knowledge, ed. Btilbring, E., Brding, A.F., Jones, A.W. & Tomit,T.,pp London:Edwrd Arnold. KURIYAMA, H. & TOMITA, T. (1970). The ction potentil in the smooth muscle of the guine pig teni coli nd ureter studied by the double sucrose-gp method. J. gen. Physiol., 55, MEISHERI, K.D., HWANG, 0. & VAN BREEMEN, C. (1981). Evidence for two seprte C2+ pthwys in smooth muscle plsmlemm. J. memb. Biol., 59, OREHEK, J., DOUGLAS, J.S. & BOUHUY, A. (1975). Contrctile responses of the guine-pig trche in vitro: Modifiction by prostglndin synthesis-inhibiting drugs. J. Phrmc. exp Ther., 194, SAKAMOTO, Y. (1970). Membrne ctivity of the guinepig stomch muscle following brium replcement of clcium ion. Jp. J. Physiol., 20, SAKAMOTO, Y. (1971). Electricl ctivity of guine-pig teni coli in clcium Locke solution. Jp. J. Physiol., 21, TAKATA, Y. (1979). The effects of ctecholmines on the smooth muscle cell membrne of rt portl vein in vrious ionic solutions. Gen. Phrmc., 10, TANIYAMA, K., YOSHIDA, N., TAKAHASHI, N. & ARAKI, H. (1977). Actions of B nd Sr ions on isolted rt ileum. Jp. J. Phrmc., 27, TRIGGLE, D.J. (1983). Clcium, the control of smooth muscle function nd bronchil hyperctivity. Allergy, 38, 1-9. UVELIUS, B., SIGURDSSON, S.B. & JOHANSSON, B. (1974). Strontium nd brium s substitutes for clcium on electricl nd mechnicl ctivity in rt portl vein. Blood Vessels, 11, (Received July 10, Revised September 5, Accepted September25, 1984.)