Adrenergic modulation of Ca2+ homeostasis in isolated fish hepatocytes

Abstract Isolated hepatocytes of the American eel ( Anguilla rostrata LeSueur) and brown bull-head ( Ictaluras nebulosus ) have been used to characterize the effects of α- and β-adrenergic agonists (epinephrine, phenylephrine, isoproterenol) and antagonists (phentolamine, propranolol) on calcium flux (influx, efflux) and cytosolic free calcium concentrations ([Ca 2+ ] i ). Bullhead hepatocytes have higher influx but lower efflux of Ca 2+ than eel hepatocytes, which may relate to the primary source for changes in [Ca 2+ ] i . Adrenergic agonists did not affect influx, but significantly enhanced efflux in eel hepatocytes (not bullhead) and [Ca 2+ ] i in both species. Increases in efflux and in [Ca 2+ ] i were blocked by α-antagonists (phentolamine) but not β-antagonists (propranolol) when present in 100-fold excess of the agonist. Isoproterenol had no significant effect on either parameter tested. This study supports our hypothesis that liver cell Ca 2+ homeostasis is modulated by a-adrenoceptor-linked pathways in these two fish species as has been previously demonstrated for the rat.