Antiarrhythmic actions of the ATP-regulated K+ current activated by pinacidil.

Abstract

We tested the hypothesis that a selective increase in membrane current, as contrasted with the decreases in currents caused by most antiarrhythmic agents, would be an effective antiarrhythmic intervention. We studied models of early afterdepolarizations (EADs), delayed afterdepolarizations (DADs), and abnormal automaticity in single canine ventricular myocytes using intracellular microelectrodes or patch electrodes. EADs were induced by injected current, Bay K 8644 (0.5-1 microM), or ketanserin (1.0 microM); DADs were induced by ouabain intoxication (2 x 10(-7) M); and abnormal automaticity was induced by exposure to barium (0.25 mM). To increase outward K+ current, we used pinacidil and the protein kinase C activator 4 beta-phorbol 12,13-dibutyrate (PDBu). Under control conditions, 10-100 microM pinacidil caused a concentration-dependent and reversible decrease in action potential duration and an increase in steady-state outward current; both effects were blocked by glibenclamide and thus presumably reflected changes in the ATP-regulated potassium current. Pinacidil increased the current required to induce EADs and abolished EADs caused by Bay K 8644 or ketanserin. After exposure of myocytes to ouabain, pinacidil caused a decrease in action potential duration and diminished or abolished DADs. Finally, pinacidil arrested abnormal automaticity caused by Ba2+. PDBu (30 nM) shortened action potential duration without altering plateau amplitude in some of the myocytes. In these cells the depolarizing current needed to produce an EAD was increased by over 70%; outward potassium current tails were also increased, an effect consistent with an increase of the repolarizing potassium current (IK). These findings show that each of the mechanisms for abnormal impulse generation can be effectively antagonized by an increase in outward current and suggest to us that selective augmentation of a repolarizing current, possibly IK, might be a reasonable antiarrhythmic intervention.

KATPChannels in the Cardiovascular System

“…An argument could therefore be made that K ATP channel opening may be anti-arrhythmic since the outward current generated will oppose these arrhythmogenic triggers. Indeed, in cellular assays, K ATP channel openers inhibit experimentally induced abnormal automaticity (481, 505, 753), or triggered arrhythmias elicited by early afterpotentials (234, 753) or late afterpotentials (481, 505,753). A counter argument, however, is that K ATP channel opening may be pro-arrhythmic (at least to some extent) since they contribute partially to the primary defect, which is the loss of K ϩ from ischemic cells and K ϩ accumulation in the ischemic zone.…”

Pinacidil Attenuates Positive Inotropic but Not Chronotropic Responses to Norepinephrine in Isolated Dog Atrial and Ventricular Preparations

“…This suggests that sufficient inhibition of Na+-K+ ATPase by ouabain inhibits the K+ATP channel mediated action in the dog atrium, although further studies are needed to clarify the precise mechanism of the inhibition. Pinacidil attenuated the action potential duration in the canine ventricular myocyte treated with a toxic dose of oua bain less than that in the ouabain non-treated myocyte (27).…”

Slow Ventricular Tachycardia Located in the Epicardium of the Left Ventricular Base and Characterized by Effects of Adenosine Triphosphate, Nicorandil and Verapamil

“…Abnormal automaticity induced by BaCl2 is also suppressed. 9 Therefore we consider that nicorandil was effective on the VT in a similar manner. 10 Furthermore, the efficacy of the drugs may be stronger in the epicardium than in the endocardium.…”