Effects of propofol on intracellular Ca2+ homeostasis in human astrocytoma cells.
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The effects of propofol, a short-acting general anesthetic, upon cell growth and Ca(2+) signaling in a human astrocytic cell line were examined. Exposure of cells to graded concentrations of propofol resulted in a dose-dependent decrease in cell number with an inhibitory concentration of cell viability (IC50) of 31.7+/-1.2 microM. To evaluate the changes in intracellular Ca(2+) homeostasis induced by propofol, cytoplasmic and mitochondrial Ca(2+) were measured by fluorescence imaging. Mitochondrial Ca(2+) increased while cytoplasmic Ca(2+) decreased significantly at a propofol concentration lower than the IC50 (10 microM for 24 h, 1 microM for 72 h). In addition, propofol diminished the Ca(2+) response induced by fetal bovine serum (FBS). To determine the source of Ca(2+) alterations induced by propofol, pharmacologic agents targeting intracellular Ca(2+) homeostasis mechanisms were used. Nifedipine, an L-type Ca(2+) channel blocker, decreased FBS-induced Ca(2+) response of control cells to a level similar to propofol treated cells. However, diazoxide (a K(+)-ATP channel opener) administered 1 h before FBS addition restored the FBS response in propofol treated cells to a level similar to control. In addition, diazoxide increased mitochondrial Ca(2+) in control cells to a level comparable to propofol treated cells suggesting activation of these channels by propofol treatment. Addition of 1 muM RU-360 (a selective blocker of the mitochondrial Ca(2+) uniporter) for 30 min prior to propofol treatment restored mitochondrial and cytoplasmic Ca(2+) to control levels. These data suggest that voltage operated Ca(2+) channels, mitochondrial Ca(2+) and K(+)-ATP channels may be targets of propofol action in astrocytes.