Effects Of K201 Research Articles

The effect of K201 on isolated working rabbit heart mechanical function during pharmacologically induced Ca2+ overload

Reduced cardiac contractility has been associated with disrupted myocardial Ca(2+) signalling. The 1,4 benzothiazepine K201 (JTV-519) acts on several Ca(2+) handling proteins and improves cardiac contractility in vivo in a variety of animal models of myocardial dysfunction. However, it is unclear whether this improvement depends on the systemic effects of K201 or if K201 reverses the effects of Ca(2+) dysregulation, regardless of the cause. The effect of K201 on cardiac mechanical function was assessed in isolated working hearts from adult rabbits, using a ventricular pressure-volume catheter. In separate experiments, the effect of K201 was investigated in hearts following pharmacologically induced Ca(2+) overload using elevated extracellular [Ca(2+) ] ([Ca(2+) ](o) ) and β-adrenoceptor stimulation. K201 induced a concentration-dependent decline in systolic function (peak pressure, dP/dt(max) and preload recruitable stroke work), lusitropy (reduced dP/dt(min) and increased end diastolic pressure) and stroke volume, independent of decreased heart rate. In separate experiments, mechanical function in hearts exposed to 4.5 mmol·L(-1) [Ca(2+) ](o) and 150 nmol·L(-1) isoprenaline declined until cessation of aortic flow (in 6 out of 11 hearts). However, all hearts perfused with the addition of 1 µmol·L(-1) K201 maintained aortic flow and demonstrated significantly improved peak systolic pressures, dP/dt(max) and dP/dt(min) . K201 significantly improved mechanical function of the heart during Ca(2+) overload. This suggests that K201 can limit the detrimental effects of elevated intracellular Ca(2+) and exert beneficial effects on cardiac contractile function, independent of systemic effects previously observed in vivo.

Effects of K-201 on the calcium pump and calcium release channel of rat skeletal muscle

The benzothiazepine derivative K-201 has been suggested as a potential therapeutic agent due to its antiarrhythmogenic action. To understand how the drug alters calcium release from the sarcoplasmic reticulum (SR), we investigated its effects on the SR calcium channel and calcium pump by single channel electrophysiology, whole-cell confocal microscopy, and ATPase activity measurements on control and post-myocardial infarcted (PMI) rat skeletal muscle. In bilayers, K-201 induced two subconductance states corresponding to approximately 24% (S(1)) and approximately 13% (S(2)) of the maximum conductance. Dependence of event frequency and of time spent in S(1) and S(2) on the drug concentration was biphasic both in control and in PMI rats, with a maximum at 50 microM. At this concentration, the channel spends 26 +/- 4% and 24 +/- 4%, respectively, of the total time in these subconductance states at positive potentials, while no subconductances are observed at negative potentials. K-201 altered the frequency of elementary calcium release events: spark frequency decreased from 0.039 +/- 0.001 to 0.023 +/- 0.001 s(-1) sarcomere(-1), while the frequency of embers increased from 0.011 +/- 0.001 to 0.023 +/- 0.001 s(-1) sarcomere(-1). Embers with different amplitude levels were observed after the addition of the drug. K-201 inhibited the Ca(2+) ATPase characterized by IC(50,contr) = 119 +/- 21 muM and n (Hill,contr) = 1.84 +/- 0.48 for control and IC(50,PMI) = 122 +/- 18 microM and n (Hill,PMI) = 1.97 +/- 0.24 for PMI animals. These results suggest that although K-201 would increase the appearance of subconductance states, the overall calcium release is reduced by the drug. In addition, the effect of K-201 is identical on calcium release channels from control and PMI rats.

Inhibition of SR Ca2+ uptake: A novel action of the RyR2–FKBP12.6 antagonist K201

See article by Loughrey et al. [13] (pages 236–246) in this issue. K201, also known as JTV519 or JTV-519, is a 1,4-benzothiazepine derivative that was developed for its protective action against Ca2+-induced myocardial damage [1]. It was subsequently shown to be protective in models of ischaemia-reperfusion injury [2,3] and heart failure (HF) [4], has been in phase II clinical trials as a protective agent against acute myocardial infarction since 2000, and is suggested to reduce reperfusion injury following percutaneous transluminal coronary angioplasty (see http://www.jti.co.jp/JTI_E/IR/FR/0111/0111-Supplementary.pdf). Although like diltiazem, to which it is structurally related, it blocks L-type-Ca2+-current (ICa,L) [5], it is a relatively non-selective blocker of cation-currents including the Na+-current [5], both background and G-protein-gated inward-rectifier K+ currents [5,6], and the rapidly-activating-delayed-rectifier-current (IKr) [6,7]. K201 is also reported to have anti-arrhythmic effects in models of atrial-fibrillation (AF) through prolongation of the effective refractory period (ERP) [6,8]. Other putative-targets for K201 include the α 1-adrenoceptor [1], annexin-V [1], protein-kinase-Cδ [3], and NO-synthase [9]. More recently, the effects of K201 on the ryanodine-receptor (RyR2), suggested to … *Department of Physiology and Pharmacology, and Bristol Heart Institute Cardiovascular Research Laboratories, School of Medical Sciences, University of Bristol, Bristol, BS8 1TD, UK. Tel.: +44 117 331 2297; fax: +44 117 331 2288. a.james{at}bristol.ac.uk

K201 modulates excitation–contraction coupling and spontaneous Ca2+ release in normal adult rabbit ventricular cardiomyocytes

The drug K201 (JTV-519) increases inotropy and suppresses arrhythmias in failing hearts, but the effects of K201 on normal hearts is unknown. The effect of K201 on excitation-contraction (E-C) coupling in normal myocardium was studied by using voltage-clamp and intracellular Ca(2+) measurements in intact cells. Sarcoplasmic reticulum (SR) function was assessed using permeabilised cardiomyocytes. Acute application of <1 micromol/L K201 had no significant effect on E-C coupling. K201 at 1 micromol/L decreased Ca(2+) transient amplitude (to 83+/-7%) without affecting I(Ca,L) or the SR Ca(2+) content. At 3 micromol/L K201 caused a larger reduction of Ca(2+) transient amplitude (to 60+/-7%) with accompanying reductions in I(Ca,L) amplitude (to 66+/-8%) and SR Ca(2+) content (74+/-9%). Spontaneous SR Ca(2+) release during diastole was induced by increasing intracellular [Ca(2+)]. At 1 micromol/L K201 reduced the frequency of spontaneous Ca(2+) release. The effect of K201 on SR-mediated Ca(2+) waves and Ca(2+) sparks was examined in beta-escin-permeabilised cardiomyocytes by confocal microscopy. K201 (1 micromol/L) reduced the frequency and velocity of SR Ca(2+) waves despite no change in SR Ca(2+) content. At 3 micromol/L K201 completely abolished Ca(2+) waves and reduced the SR Ca(2+) content (to approximately 73%). K201 at 1 micromol/L reduced Ca(2+) spark amplitude and frequency. Assays specific to SR Ca(2+)-ATPase and RyR2 activity indicated that K201 inhibited both SR Ca(2+) uptake and release. K201 modifies E-C coupling in normal cardiomyocytes. A dual inhibitory action on SERCA and RyR2 explains the ability of K201 to suppress spontaneous diastolic Ca(2+) release during Ca(2+) overload without significantly affecting Ca(2+) transient amplitude.

New 1,4‐benzothiazepine derivative, K201, demonstrates cardioprotective effects against sudden cardiac cell death and intracellular calcium blocking action

AbstractIn order to find drugs with suppressive effects against sudden cardiac cell death due to myofibrillar overcontraction, the cardioprotective effects of a new 1,4‐benzothiazepine derivative, 4‐[3‐{1‐(4‐benzyl)piperidinyl}propionyl]‐7‐methoxy‐2,3,4,5‐tetrahydro‐1,4‐benzothiazepine, K201, in comparison with five other compounds, including a representative α‐antagonist, β‐antagonist, and Ca2+ channel antagonists, were investigated in an experimental myofibrillar overcontraction model of isolated rat heart. In addition, the effects of K201 on the contraction of isolated vascular smooth muscle of rat aorta and on the binding of cardiac annexin V with actin were compared with those of diltiazem and KT362. The degree of myofibrillar overcontraction was histologically scored on a four‐grade scale (0, 1, 2, and 3) as myocardial injury score (MIS). Suppressive effects of myofibrillar overcontraction could not be observed with nicorandil and prazosin at 10−5 M. Propranolol at 10−5 M, verapamil at 10−6 M, and diltiazem at 10−6 M demonstrated a significant suppressive effect with MIS of 1.0 ± 0.4 (P &lt; 0.01), 1.5 ± 0.3 (P &lt; 0.01), and 1.5 ± 0.3 (P &lt; 0.01), respectively. K201, even at 10−7 M, displayed significant suppression with MIS of 1.8 ± 0.2 (P &lt; 0.01). K201 inhibited contraction of isolated vascular muscle induced by K+ (40 mM) and NE (1 μM) at almost the same concentration. The lC50 ratio (NE/K+) of K201 was 2.3. The inhibition by K201 of the response to K+ was less marked than that by diltiazem. Its inhibition of the response to NE was greater than that by diltiazem or KT362. K201 demonstrated an inhibitory effect on binding of cardiac annexin V with actin dependent on calcium concentration, but diltiazem and KT362 did not demonstrate any action to inhibit this reaction. These results indicate that K201 was a more effective cardioprotectant than propranolol, verapamil, and diltiazem in the experimental myofibrillar overcontraction model. K201 has intracellular Ca2+ blocking action in addition to weak α‐1 adrenergic blocking activity and Ca2+ blocking activity. © 1994 Wiley‐Liss, Inc.