Inhibitory effects of JTV-519, a novel cardioprotective drug, on potassium currents and experimental atrial fibrillation in guinea-pig hearts

Abstract

1. We investigated the effects of JTV-519 (4-[3-(4-benzylpiperidin-1-yl)propionyl]-7-methoxy-2,3,4, 5-tetrahydro-1,4-benzothiazepine monohydrochloride), a novel cardioprotective drug, on the repolarizing K(+) currents in guinea-pig atrial cells by use of patch-clamp techniques. We also evaluated the effects of JTV-519 on experimental atrial fibrillation (AF) in isolated guinea-pig hearts. 2. In atrial cells stimulated at 0.2 Hz, JTV-519 in concentrations of 0.3 and 1 microM slightly prolonged the action potential duration (APD). The drug also reversed the action potential shortening induced by the muscarinic agonist carbachol in a concentration-dependent manner. 3. The muscarinic acetylcholine receptor-operated K(+) current (I(K.ACh)) was activated by the extracellular application of carbachol (1 microM), adenosine (10 microM) or by the intracellular loading of GTP gamma S (100 microM). JTV-519 inhibited the carbachol-, adenosine- and GTP gamma S-induced I(K.ACh) with the IC(50) values of 0.12, 2.29 and 2.42 microM, respectively, suggesting that the drug may inhibit I(K.ACh) mainly by blocking the muscarinic receptors. 4. JTV-519 (1 microM) inhibited the delayed rectifier K(+) current (I(K)). Electrophysiological analyses indicated that the drug preferentially inhibits I(Kr) (rapidly activating component) but not I(Ks) (slowly activating component). 5. In isolated hearts, perfusion of carbachol (1 microM) shortened monophasic action potential (MAP) and effective refractory period (ERP), and lowered atrial fibrillation threshold (AFT). Addition of JTV-519 (1 microM) inhibited the induction of AF by prolonging MAP and ERP. 6. We conclude that JTV-519 can exert antiarrhythmic effects against AF by inhibiting repolarizing K(+) currents. The drug may be useful for the treatment of AF in patients with ischaemic heart disease.

Figure 1

Effects of JTV-519 on the action potential in the absence (A) and presence of carbachol (1 μM) (B) in guinea-pig atrial cells. Superimposed records of action potentials recorded before (control), after exposure to JTV-519 (JTV) (0.3 and 1 μM) and washout (W.O.) of the drug are shown in A. Superimposed records of action potentials after exposure to carbachol (CCh) and carbachol plus JTV-519 are shown in B. Summarized data of changes of action potential duration at 90% repolarization level (APD₉₀) after JTV-519 in the absence and presence of muscarinic stimulation are indicated on the right side. The values are expressed as mean±s.e.mean of 7–9 experiments. +P<0.05 vs control, ^*P<0.05 vs carbachol alone.

Figure 2

Effects of JTV-519 on the muscarinic acetylcholine receptor-operated K⁺ current (I_K.ACh) in isolated guinea-pig atrial cells. I_K.ACh was activated by the extracellular application of carbachol (CCh, 1 μM), adenosine (Ado, 10 μM) or intracellular loading of GTPγS (100 μM). Original current traces obtained from atrial cells held at −40 mV are shown in upper panels. Concentration-response curves for the inhibitory effects of JTV-519 on the I_K.ACh activated by carbachol, adenosine and GTPγS are shown in lower panel. Per cent inhibition of the outward current is indicated on the ordinate and the concentrations of JTV-519 are on the abscissa. Values are expressed as mean±s.e.mean of 5–9 experiments.

Figure 3

Effects of JTV-519 on the current-voltage relationships of the I_K.ACh induced by carbachol (1 μM), adenosine (10 μM) and GTPγS (100 μM). The actual current traces of the quasi-steady-state current before, after the activation of I_K.ACh and after the application of JTV-519 are superimposed in upper panels. The current density of the membrane current measured at each voltage is summarized in lower panels. Values are expressed as mean±s.e.mean of 4–5 experiments.

Figure 4

Effects of JTV-519 on the delayed rectifier K⁺ current in guinea-pig atrial cells. (A) Actual current traces elicited by 300 ms depolarizing pulses from a holding potential of −40 mV before (left) and after 1 μM JTV-519 (right). The external solution contained 1 μM nisoldipine. (B) Graphs showing I_K measured at the end of 300 ms test pulse to the indicated test potential (I_K,depo, left) and that measured after repolarization to −40 mV from the indicated test potential (I_K,tail, right). (C) Current-voltage relation of JTV-519-sensitive I_K during depolarization pulses to various potentials. (D) Concentration-response curve for the inhibitory effect of JTV-519 on I_K,depo at 0 mV. Per cent inhibition of I_K,depo is indicated on the ordinate and the concentrations of JTV-519 are on the abscissa. Values are expressed as mean±s.e.mean of 5–6 experiments. ^*P<0.05 vs control.

Figure 5

Effects of JTV-519 on the delayed rectifier K⁺ current (I_K) in the presence of the I_Kr blocker E-4031. (A) Current traces elicited by 300 ms depolarizing pulses from a holding potential of −40 mV in the control condition, in the presence of 5 μM E-4031, after the addition of 3 μM JTV-519 and after washout. (B) Graphs showing I_K measured at the end of 300 ms test pulses to the indicated test potential (I_K,depo, upper) and that measured after repolarization to −40 mV from the indicated potential (I_K,tail, lower). Data represent mean±s.e.mean of five cells. +P<0.05 vs control.

Figure 6

Effects of JTV-519 (1 μM) on the carbachol (CCh, 1 μM)-induced changes in monophasic action potential (MAP), effective refractory period (ERP) and conduction time (CT) in isolated guinea-pig hearts. Actual records of MAP during control period and after carbachol and carbachol plus JTV-519 are shown in A. Summarized data of changes in MAP at 90% repolarization level (MAP₉₀), ERP and CT are shown in B. The values are expressed as mean±s.e.mean of six hearts. +P<0.05 vs control, ^*P<0.05 vs carbachol alone.