Chronic intermittent hypoxia alters Ca2+ handling in rat cardiomyocytes by augmented Na+/Ca2+ exchange and ryanodine receptor activities in ischemia-reperfusion.

This study examined Ca2+ handling mechanisms involved in cardioprotection induced by chronic intermittent hypoxia (CIH) against ischemia-reperfusion (I/R) injury. Adult male Sprague-Dawley rats were exposed to 10% inspired O2 continuously for 6 h daily from 3, 7, and 14 days. In isolated perfused hearts subjected to I/R, CIH-induced cardioprotection was most significant in the 7-day group with less infarct size and lactate dehydrogenase release, compared with the normoxic group. The I/R-induced alterations in diastolic Ca2+ level, amplitude, time-to-peak, and the decay time of both electrically and caffeine-induced Ca2+ transients measured by spectrofluorometry in isolated ventricular myocytes of the 7-day CIH group were less than that of the normoxic group, suggesting an involvement of altered Ca2+ handling of the sarcoplasmic reticulum (SR) and sarcolemma. We further determined the protein expression and activity of 45Ca2+ flux of SR-Ca2+-ATPase, ryanodine receptor (RyR) and sarcolemmal Na+/Ca2+ exchang...