Involvement of anion exchange in the hypoxia/reoxygenation-induced changes in pHi and [Ca2+]i in cardiac myocyte

Abstract

The involvement of Cl−/HCO3− exchange in hypoxia/reoxygenation-induced changes in pHi and Ca2+ concentration ([Ca2+]i) was examined in rat ventricular myocytes. During 10-min hypoxia, the initial pHi (7.21±0.04) fell to below 6.8. Subsequent reperfusion with reoxygenated buffer returned this acidic pHi to the neutral range with increases in [Ca2+]i. These responses were reduced by the removal of Cl− or HCO3− and by the addition of anion exchange inhibitors, SITS (4-acetamido-4′isothiocyanato-stilbene-2,2′disulfonic acid) and DIDS (4,4′-diisothiocyano-stilbene-2,2′-disulfonic acid), while inhibitors for the Cl− channel and Na+/K+/2Cl− cotransport were without effects. The hypoxia-induced acidification was attenuated by protein kinase C inhibitors, calphostin C and chelerythrine, but not by a protein kinase A inhibitor, KT5720. Under normoxic condition, protein kinase C activation induced a SITS-sensitive acidification. Furthermore, in electrically driven rat papillary muscle, SITS and DIDS improved the recovery of developed tension during the reoxygenation. These results suggest that the hypoxia-induced decrease in pHi is mediated at least in part by anion exchange stimulation through protein kinase C activation, and this exchange takes part in the reoxygenation-induced Ca2+ overload as well as contractile dysfunction.