Modulation of palmitate-induced cardiomyocyte cell death by interventions that alter intracellular calcium

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The objective of this study was to investigate whether palmitate-induced cell death in cardiomyocytes was dependent on alterations of intracellular calcium ([Ca2+]I). Specifically, we sought to determine whether palmitate might produce a cellular calcium overload by increasing calcium influx into the cell or by altering sarcoplasmic reticulum (SR) calcium transport. We also determined whether palmitate's effects might be modulated by agents that alter [Ca2+)I. Treatment of chick embryonic cardiomyocytes in culture with palmitate (100uM) produced a significant (P>0.05) and 42.9 ± 5.3% reduction in cell survival or increase in cell death. As determined by FURA-2 measurement of [Ca2+]I, the cytotoxicity of palmitate on cardiomyocytes did not appear to be mediated through acute increases in [Ca2+]I. In contrast, the unsaturated fatty acid, arachidonic acid increased [Ca2+]I. The calcium ionophore ionomycin significantly (P<0.05) increased palmitate-induced cardiomyocyte cell death. The effects of ionomycin and palmitate, however, were additive, suggesting palmitate and ionomycin acted in an independent manner to induce cell death. Furthermore, in contrast to palmitate, an ionomycin-induced increase in [Ca2+]Iwas demonstrated in these cells. Inhibition of SR calcium reuptake by thapsigargin, which acutely increases [Ca2+]I, also significantly (P>0.05) increased palmitate-induced cardiomyocyte death. Again, these two agents most likely acted in an independent manner because of the additive nature of the effect of palmitate and thapsigargin on cell viability. Pamitate-induced cardiotoxicity was not mediated through release of [Ca2+]Ifrom SR or through voltage-operated channels on plasma membranes, as neither SR calcium depletion by low concentrations of ryanodine nor blockade of the voltage-operated calcium channel with nifedipine significantly altered palmitate-induced cardiomyocyte death. These data suggest that palmitate-induced cardiac cell death is enhanced by increases in [Ca2+]Iand highlights the potential adverse effect of a combination of palmitate with conditions that increase [Ca2+]Iin cardiomyocytes.