Lactate-induced vascular relaxation in porcine coronary arteries is mediated by Ca2+-activated K+ channels

Under ischemic conditions and during strenuous exercise, lactate concentrations increase in coronary artery smooth muscle cells. Although lactate causes pH-independent vasorelaxation, the mechanisms responsible for this effect are unclear. We investigated the effect of lactate on K+ channels in smooth muscle cells from porcine coronary arteries. Neutralized lactate (3-100 mm) induced vasorelaxation in ring segments of porcine coronary arteries precontracted with KCl in a dose-dependent manner. One millimolar tetraethylammonium (TEA), an inhibitor of Ca2+-activated K+ channels (KCa channels), reversed the lactate-induced relaxation, while 60 microM glibenclamide, an inhibitor of ATP-sensitive K+ channels (KATP channels), did not. In both inside-out and cell-attached patch clamp technique with cultured smooth muscle cells, the KCa channels were activated by lactate. In inside-out patches, lactate activated KCa channels, even under acidic conditions. This is in contrast to the effect of H+ which inactivated KCa channels. We conclude that vasodilation of porcine coronary arteries induced by lactate is, at least in part, mediated by activation of KCa channels. This effect may be self-protective by maintaining coronary blood flow during ischemia.