Ionchannels and channelopaties in the heart

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1 Ionchannels and channelopaties in the heart Csatorna müködés Több betegség Drugok kapcsolodása csat.hoz Sejtekbe ioncsat.expresszios módszerek, bemutatása Viktória Szőts

2 Action of membrane transport protein ATP-powered pump Ion chanels Transporters ions/s ions/s ions/s

3 Nerbonne et al. Circ Res. 2001;89:

4 Membrane topology of the Kv and Kir2.x K-ionchannels Voltage gated K + channel Inward rectifier K + channel Kv channel CO 2 CO 2 CO 2 H5 H5

5 Kv complex MiRP N N α C C KChAP β PSD

6 Különbözı Ioncsatorna alegységek összeszerelıdése Abott et al Neuropharm. 2004

7 Voltage-Gated Calcium Channels Voltage-gated calcium channels are heteromultimers composed of an α1 subunit and three auxiliary subunits, 2-δ, β and γ. The α1 subunit forms the ion pore and possesses gating functions and, in some cases, drug binding sites. Ten α1 subunits have been identified, which, in turn, are associated with the activities of the six classes of calcium channels. L-type channels have α1c (cardiac), α1d (neuronal/endocrine), α1s (skeletal muscle), and α1f (retinal) subunits; The α1 subunits each have four homologous domains (I-IV) that are composed of six transmembrane helices. The fourth transmembrane helix of each domain contains the voltage-sensing function. The four α1domains cluster in the membrane to form the ion pore. The β-subunit is localized intracellularly and is involved in the membrane trafficking of α1subunits. The γ-subunit is a glycoprotein having four transmembrane segments. The α2 subunit is a highly glycosylated extracellular protein that is attached to the membrane-spanning d-subunit by means of disulfide bonds. The α2-domain provides structural support required for channel stimulation, while the δ domain modulates the voltage-dependent activation and steady-state inactivation of the channel.

8 Molecular assembly of ion channels Cavα Kvα Kir

9 Activation and Inactivation Of The Sodium Channel Sodium channels are characterized by voltagedependent activation, rapid inactivation, and selective ion conductance. Depolarization of the cell membrane opens the ion pore allowing sodium to passively enter the cell down its concentration gradient. The increase in sodium conductance further depolarizes the membrane to near the sodium equilibrium potential. Inactivation of the sodium channel occurs within milliseconds, initiating a brief refractory period during which the membrane is not excitable. The mechanism of inactivation has been modeled as a "hinged lid" or "ball and chain", where the intracellular loop connecting domains III and IV of the a subunit closes the pore and prevents passage of sodium ions.

10 Ionic currents and ion transporters responsible for cardiac action potential Abriel H. et al., Swiss Med Wkly 2004, w. ch

11 Proposed cellular mechanism for the development of Torsade de pointes in the long QT syndrome

12 Risk factors for developing Torsade de pointes Genetic variants (polymorphysm or mutations) Abriel H. et al., Swiss Med Wkly 2004,

13 Ionic current, proteins and genes associated with inherited arrhythmias Napolitano et al. Pharm. & ther. 2006,110:1-13

14 Congenital and aquired forms of long QT syndromes Abriel H. et al., Swiss Med Wkly 2004, w. ch

15 K+, Na+ channel LQT-associated genes and proteins Current Genes Disease I To1 I Ks I Kr I Na I k1 I kur I kach I katp I CaL Kv4.3 KvLQT1(KCNQ1) Mink (KCNE1) HERG (KCNH2) MiRP1 (KCNE2) SCN5A Kir2.1 (KCNJ2) Kv1.7(KCNA7),Kv1.5 Kir3.4 Kir6.2 Cav1.2 (CACNA1c) LQT LQT1, JLN1 LQT5, JLN2 LQT2 LQT6, FAF LQT3 Brugada Syndrome, Cardiac conduction defect, Sick sinus syndrome LQT7 Andersen-Tawil Syndrome Progressziv familial heart Block1 LQT8 Timothy Syndrome

16 Prolonged QT interval on ECG (reflects prolonged APD) APD governed by a delicate balance between inward (Na + or Ca + ) and outward (K + ) ionic current Affecting the Na + or Ca + channel prolong APD via gain-offfunction mechanism, while mutation in genes encoding K + channel by loss-off-function mechanism

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18 Gene mutations in LQT1 and LQT2 HERG KCNH2 KvLQT1 KCNQ1 LQT2 LQT1

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20 Molecular structure and the membrane topology of the HERG channel Mutations in HERG channel

21 Pivotal role of Ser phosphorilation as a regulatory mechanism in Cav1.2 mode1/mode2 gating. Timothy s syndrome

22 Current Genes Disease I Kr I K1 I Ks HERG (KCNH2) Kir2.x (KCNJ2) KvLQT1(KCNQ1) ShortQT I Ca CASQ2 CPVT catecholamine-induced (Calsequestrin2) polymorphic CPVT ventricular tachycardia RyR2 CPVT β 1 -adrenoceptor (β 1 -AR) β 2 -adrenoceptor (β 2 -AR) Kv3.1, Kv3.3 Risk factor, modify disease or influence progression of disease Risk factor, modify disease or influence progression of disease AF

23 Complexity of protein-protein interaction in cardiomyocytes

24 Missense mutation in calsequestrin2 (CASQ2) wild type Syncope Seizures or Sudden death In response to Physical activity or Emotional stress mutant Associated with autosomal recessive catecholamineinduced polymorphic ventricular tachycardia (CPVT)

25 Kir2.1 ionchannel has an autosomal dominant mutation in Andersen-Tawil Syndrome Cardiac arrhytmias Periodic paralysis Dysmorphic bone structure(scoliosis, low-set ears, small chin, broad forehead

26 Facial and sceletal features in Andersen- Tawil syndrome

27 GIRK mutation

28 ANP role

29 Gene-specific mutation study Genexpression study Microarray, qrt-pcr Proteomica

30 Kir2.x analysis by RT-PCR kir2.x mrna in dog & human Kir2.1 Kir2.2 Kir2.3 Kir2.4 HUMAN DOG

31 Expression of Kv1.5 protein in human and dog kda RV LV RA LA RV LV DOG HUMAN 6 RA LA Relative amount of Kv HUMAN DOG n=12 n= 6 LV LA

32 Co-localization of Kvβ β2 auxillary subunit with Kv1.5 in dog left ventricular myocytes Kv1.5-FITC Kvβ β2-texas red 100 µ Kv1.5-FITC Kvβ β2-texas red

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