Intermittent hypoxia protects the rat heart against ischemia/reperfusion injury by activating protein kinase C

Abstract

The aim of this study was to investigate whether and how protein kinase C (PKC) was involved in the protection afforded by intermittent hypoxia (IH) and the subcellular distribution of different PKC isozymes in rat left ventricle. Post-ischemic recovery of left ventricular developed pressure and ±dP/dtmax in IH hearts were higher than those of normoxic hearts. Chelerythrine (CHE, 5 μM), a PKC antagonist, significantly inhibited the protective effects of IH, but had no influence on normoxic hearts. CHE significantly reduced the effect of IH on the time to maximal contracture (Tmc), but had no significant effect on the amplitude of maximal contracture (Amc) in IH group. In isolated normoxic cardiomyocytes, [Ca 2+] i, measured as arbitrary units of fluorescence ratio (340nm/380nm) of fura-2, gradually increased during 20 min simulated ischemia and kept at high level during 30 min reperfusion. However, [Ca 2+] i kept at normal level during simulated ischemia and reperfusion in isolated IH cardiomyocytes. In normoxic myocytes, [Na +] i, indicated as actual concentration undergone calibration, gradually increased during 20 min simulated ischemia and quickly declined to almost the same level as that of pre-ischemia during 30 min simulated reperfusion. However, in IH myocytes, [Na +] i increased to a level lower than the corresponding of normoxic myocytes during simulated ischemia and gradually reduced to the similar level as that of normoxic myocytes after simulated reperfusion. 5 μM CHE greatly increased the levels of [Ca 2+] i and [Na +] i during ischemia and reperfusion in normoxic and IH myocytes. In addition, we demonstrated that IH up-regulated the baseline protein expression of particulate fraction of PKC-α, ɛ, δ isozymes. There is no significant difference of protein expression of PKC-α, ɛ, δ isozymes in cytosolic fraction between IH and normoxic group. The above results suggested that PKC contributed to the cardioprotection afforded by IH against ischemia/reperfusion (I/R) injury; the basal up-regulation of the particulate fraction of PKC-α, ɛ, δ isozymes in IH rat hearts and the contribution of PKC to the elimination of calcium and sodium overload might underlie the mechanisms of cardioprotection by IH.