In intermittent hypoxia adaptation (IHA) rat cardiomyocytes, the relationship between activated protein kinase C and intracellular acidification regulation during ischemia-reperfusion (I/R) was tested. Using [H+] indicator BCECF-AM, we analyzed the alterations of intracellular pH (pH(i)) in normoxia, and IHA rat cardiomyocytes during I/R. With the time of ischemia, the pH(i) decreased progressively in normal cardiomyocytes, but fewer alterations in IHA myocytes. Treatment of IHA and normoxia cardiomyocytes with 5 mu M chelerythrine delayed the pH(i) recovery during post-ischemia. In contrast, the application of 1 mu M phorbol 12-myristate 13-acetate in normoxia cardiomyocytes preserved the pH(i) during I/R, which was similar to that in IHA cardiomyocytes. Our data suggest that the stable PKC activation might contribute to preservation of the pH(i), which may be beneficial to maintain cardiac function during I/R in IHA rats. (c) 2007 Elsevier Inc. All rights reserved.