Involvement of anion exchange in the hypoxia/reoxygenation-induced changes in pH(i) and

The involvement of Cl(-)/HCO(3)(-) exchange in hypoxia/reoxygenation-induced changes in pH(i) and Ca(2+) concentration ([Ca(2+)](i)) was examined in rat ventricular myocytes. During 10-min hypoxia, the initial pH(i) (7.21+/-0.04) fell to below 6.8. Subsequent reperfusion with reoxygenated buffer returned this acidic pH(i) to the neutral range with increases in [Ca(2+)](i). These responses were reduced by the removal of Cl(-) or HCO(3)(-) 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 pH(i) is mediated at least in part by anion exchange stimulation through protein kinase C activation, and this exchange takes part in the reoxygenation-induced Ca(2+) overload as well as contractile dysfunction.