EFFECTS OF ENERGY LIMITATION ON CA2-TOLERANT AND ANOXIA-INTOLERANT HEPATOCYTES( AND K+ HOMEOSTASIS IN ANOXIA)

Effects of energy limitation on Ca2+ and K+ homeostasis in anoxia-tole rant and anoxia-intolerant hepatocytes. Am. J. Physiol. 273 (Regulator y Integrative Comp. Physiol. 42): R307-R316, 1997.-To gain more insigh t into the mechanistic basis of anoxia tolerance and intolerance, a co mparative study was conducted on calcium homeostasis in goldfish and t rout hepatocytes subjected to different forms of energy limitation. Us ing the fluorescent Ca2+ indicator fura 2, we observed that both chemi cal anoxia and true anoxia led to an increase of the concentration of cytosolic free calcium (Ca-i(2+)) in the anoxia-sensitive hepatocytes of rainbow trout, whereas Ca-i(2+) was maintained at control levels in the anoxia-tolerant hepatocytes of goldfish. Various lines of evidenc e suggest an intracellular origin of the Ca2+ increase observed in tro ut cells. Cyclosporin A, a specific inhibitor of the mitochondrial per meability transition pore in mammalian cells, was ineffective in preve nting the Ca2+ increase, whereas a high dose of fructose depressed the Ca2+ surge by similar to 50%. The latter effect was not accompanied b y improvement of the energetic state of the cells. A comparison of che mical anoxia with true (physiological) anoxia revealed that both treat ments affected energy metabolism to a similar degree in trout hepatocy tes, whereas the decrease of ATP seen in goldfish hepatocytes during c hemical anoxia was absent during true anoxia. Elevation of Ca-i(2+) wi th the calcium ionophore A-23187 led to a decoupling of unidirectional K+ fluxes in both normoxic and anoxic trout cells, whereas in goldfis h hepatocytes the coupling of K+ fluxes was not affected by the rise o f Ca-i(2+).