The Effect of Sarcolemmal Cholesterol Content on the Tolerance to Anoxia in Cardiomyocyte Cultures

To determine whether the sarcolemmal-free cholesterol content influences the tolerance to anoxia in cultured neonatal rat cardiomyocytes, we modulated the free cholesterol content of the cultures, and determined the time course of anoxia-induced cell death. Incubation for 5 h with liposomes having a free cholesterol to phospholipid molar ratio of 2, 0.5, and 0, resulted in a change of cellular free cholesterol content by + 54.7 ± 5.8% (P<0.001), by -5.2 ± 6.3% (n.s.), and by -22.1 ± 4.9% (P<0.01), respectively, when compared to cultures incubated without liposomes (control). In cells which were loaded with cholesterol, it was verified that the extra cholesterol was transferred predominantly to the sarcolemma, which was associated with a decrease in sarcolemmal fluidity. In cells which underwent cholesterol reduction it was verified that free cholesterol was retracted selectively from the sarcolemma, associated with an increase in sarcolemmal fluidity. Cellular enrichment with free cholesterol caused a delay of anoxia-induced release of lactate dehydrogenase (LDH): the time at which half-maximal release of LDH was reached (LDH50%) occurred later by 35.5 ± 3.4 min (P<0.001) compared to anoxic control cultures. Cholesterol reduction diminished the tolerance to anoxia: LDH50% occurred earlier by 36.4 ± 7.8 min (P<0.01), compared to anoxic control cultures. Cultures which were incubated with liposomes having a free cholesterol to phospholipid molar ratio of 0.5 had unchanged sarcolemmal free cholesterol content, unchanged sarcolemmal fluidity, and an unchanged LDH50% during anoxia in comparison to control cultures, excluding any effect of the incubation with liposomes per se. The present study indicates that the sarcolemmal free cholesterol content of cardiomyocytes is a determinant of their tolerance to anoxia.