Phospholipid lysophosphatidylcholine as a metabolic trigger and HERG as an ionic pathway for extracellular K accumulation and "short QT syndrome" in acute myocardial ischemia.

The most profound abnormalities during acute myocardial ischemia are extracellular K(+) accumulation (K(+)- upward arrow) and shortening of action potential duration or QT interval (APD- downward arrow or QT- downward arrow), which are pivotal in the genesis of ischemic arrhythmias and sudden cardiac death. The ionic mechanisms however remained obscured. We performed studies in a rabbit model of acute global myocardial ischemia in order to explore ionic and metabolic mechanisms for ischemic K(+)- upward arrow and QT- downward arrow. Exogenous 1-palmitoyl-lysophosphatidylcholine (LPC-16) mimicked the low-perfusion ischemia to produce significant K(+)- upward arrow and QT- downward arrow. The K(+)- upward arrow and QT- downward arrow induced by either LPC-16 or ischemia were prevented by dofetilide, a blocker of rapid delayed rectifier K(+) current (I(Kr)), but not by blockers for other K(+) channels. Consistently, dofetilide efficiently abolished the ventricular tachy-arrhythmias induced by ischemia or LPC-16. LPC-16 remarkably shortened APD and enhanced the function of I(Kr) and HERG (the pore-forming subunit of I(Kr)). The effects of LPC-16 manifested with shorter APD (faster repolarization rate) and at more negative potential (membrane repolarization). Dofetilide abolished the I(Kr)/HERG enhancing and APD shortening effects of LPC-16. Our results suggest that LPC-16 accumulation/HERG enhancement may be a link between metabolic trigger and ionic pathway for ischemic K(+)- upward arrow and QTc- downward arrow. This represents the first documentation of I(Kr)/HERG as the ionic mechanism in ischemic K(+)- upward arrow and QTc- downward arrow. Inhibition of LPC-16 production and accumulation and/or of I(Kr)/HERG may be a promising therapeutic strategy to attenuate the incidence of lethal arrhythmias associated with ischemic heart disease.