Transient increases of intracellular Ca²⁺ induced by volatile anesthetics in rat hepatocytes

The affects of volatile anesthetics on mobilization of intracellular Ca²⁺ was monitored in primary cultures of rat hepatocytes using the fluorescent Ca²⁺ probe Fura-2. The use of Fura-2 was limited by several factors which complicated the quantitative analysis of the results, such as: (i) a high rate of dye leakage; (ii) changes in the redox state of the hepatocytes which interfered with the fluorescence produced by the dye at various excitation wavelengths; (iii) compartmentalization of the dye producing high local intracellular concentrations; and, of particular importance for this study, (iv) enhanced photobleaching of the dye in the presence of halothane. To aid in the interpretation of the Fura-2 data, the Ca²⁺-sensitive photoprotein aequorin was also used to monitor changes in [Ca²⁺]_i. The aequorin and Fura-2 techniques qualitatively yielded the same result, that the volatile anesthetic agents halothane, enflurane, and isoflurane induce an immediate and transient increase of [Ca²⁺]_i. The durations of these transients were approximately between 5 and 10 min and were not related to any evident acute cell toxicity. The [Ca²⁺]_i increases induced by the volatile anesthetic agents were dose-dependent, with halothane the most potent. The exact mechanism governing these increases in [Ca²⁺]_i induced by these anesthetics in rat hepatocytes is inknown, but is likely to involve effects on both the cell surface membrane and endoplasmic reticulum components of the signal transducing system.