Metabolic inhibition activates a non selective current through connexin hemichannels in isolated ventricular myocytes

Intracellular Na+ accumulation and K+ loss play important roles in the path ogenesis of arrhythmias and injury in the ischemic heart. We investigated t he role of metabolically sensitive connexin hemichannels as a potential rou te for Na+ influx and K+ efflux during ischemia, using dye uptake and elect rophysiological measurements to assay hemichannel activity in isolated rabb it ventricular myocytes. Consistent with the known size selectivity of conn exin hemichannels, similar to 50% of myocytes exposed to either low extrace llular Ca2+ tan established method for opening connexin hemichannels) or to metabolic inhibitors (a recently described method for opening hemichannels ) accumulated fluorescent dyes with <1000 MW (propidium iodide and calcein) , but excluded a larger dye with 1500-3000 MW (dextran-rhodamine). Using th e whole cell patch clamp technique, we found that metabolic inhibitors acti vated a non-selective current permeant to both small and large cations, and blocked by La3+, similar to the properties of connexin 43 when overexpress ed in human embryonic kidney (HEK) cells. These findings indicate that isol ated cardiac myocytes endogenously express metabolically-sensitive connexin hemichannels. If activated during ischemia, these hemichannels could contr ibute significantly to altered ionic fluxes promoting arrhythmias and myoca rdial injury. (C) 2000 Academic Press.