Selective block of sarcolemmal IKATP in human cardiomyocytes using HMR 1098.

PURPOSE: Activation of the myocardial, ATP-dependent potassium current (IK(ATP)) during ischemia causes shortening of the action potential duration thereby increasing dispersion of repolarization between ischemic and non-ischemic myocardium and predisposing to reentrant arrhythmias. The IK(ATP) inhibitor HMR1098 allows selective block of the sarcolemmal myocardial K(ATP)-channel in various animal species. Therefore, we studied the concentration and pH-dependence of HMR1098 in human ventricular myocytes.
METHODS: Human ventricular cardiomyocytes were isolated enzymatically. IK(ATP) was measured with the patch-clamp technique in whole cell configuration at 35 degrees C. Action potentials were recorded using Amphotericine B in perforated patch conditions. In voltage clamp experiments, the K(ATP)-channel was activated by application of 1 microM rilmakalim, a K(ATP)-channel opener. In action potential recordings, 0.1 microM rilmakalim was used.
RESULTS: At physiological pH (pH = 7.3) half-maximal block of the rilmakalim-induced current occurred at 0.42 +/- 0.008 microM HMR1098 (at 0 mV membrane potential); under acidic conditions as can be expected to be present under ischemic conditions (pH = 6.5), half-maximal block was achieved at markedly lower concentrations (IC(50) = 0.24 +/- 0.009 microM). In current clamp experiments, block of IK(ATP) by HMR1098 was capable of reversing the action potential shortening induced by rilmakalim, and restored the action potential plateau.
CONCLUSIONS: HMR1098 appears to be useful to prevent IK(ATP)-induced shortening of the action potential in human ventricular myocardium. More acidic conditions, as observed in ischemia, increase the sensitivity to HMR1098, indicating a more potent effect in ischemic myocardium. Thus, HMR1098 may be a useful agent to prevent action potential shortening and dispersion of repolarization during ischemia, which may protect against ischemia induced ventricular arrhythmias.