Volumetric and ionic responses of goldfish hepatocytes to anisotonic exposure and energetic limitation

The relationship between cell volume and K+ transmembrane fluxes of goldfish (Carassius auratus) hepatocytes exposed to anisotonic conditions or energetic limitation was studied and compared with the response of hepatocytes from trout (Oncorhynchus mykiss) and rat (Rattus rattus). Cell volume was studied by video- and fluorescence microscopy, while K+ fluxes were assessed by measuring unidirectional Rb-86(+) fluxes. In trout and rat hepatocytes, hyposmotic (180mosmol1(-1)) exposure at pH 7.45 caused cell swelling followed by a regulatory volume decrease (RVD), a response reported to be mediated by net efflux of KCl and osmotically obliged water. By contrast, goldfish hepatocytes swelled but showed no RVD under these conditions. Although in goldfish hepatocytes a net (86Rb+)K+ efflux could be activated by N-ethylmaleimide, this flux was not, or only partially, activated by hyposmotic swelling (120-180 mosmol1(-1)). Blockage of glycolysis by iodoacetic acid (IAA) did not alter cell volume in goldfish hepatocytes, whereas in the presence of cyanide (CN-), an inhibitor of oxidative phosphorylation, or CN- plus IAA (CN-+IAA), cell volume decreased by 3-7%. Although in goldfish hepatocytes, energetic limitation had no effect on (86Rb+)K+ efflux, (86Rb+)K+ influx decreased by 57-66% in the presence of CN- and CN-+IAA but was not significantly altered by IAA alone. Intracellular K+ loss after 20 min of exposure to CN- and CN-+IAA amounted to only 3% of the total intracellular K+. Collectively, these observations suggest that goldfish hepatocytes, unlike hepatocytes; of anoxia-intolerant species, avoid a decoupling of transmembrane K+ fluxes in response to an osmotic challenge. This may underlie both the inability of swollen cells to undergo RVD but also the capability of anoxic cells to maintain intracellular K+ concentrations that are almost unaltered, thereby prolonging cell survival.