Adrenergic modulation of Ca2+ homeostasis in isolated fish hepatocytes

Isolated hepatocytes of the American eel (Anguilla rostrata LeSueur) and brown bullhead (Ictaluras nebulosus) have been used to characterize the effects of alpha- and beta-adrenergic agonists (epinephrine, phenylephrine, isoproterenol) and antagonists (phentolamine, propranolol) on calcium flux (influx, efflux) and cytosolic free calcium concentrations ([Ca2+]i). Bullhead hepatocytes have higher influx but lower efflux of Ca2+ than eel hepatocytes, which may relate to the primary source for changes in [Ca2+]i. Adrenergic agonists did not affect influx, but significantly enhanced efflux in eel hepatocytes (not bullhead) and [Ca2+]i in both species. Increases in efflux and in [Ca2+]i were blocked by alpha-antagonists (phentolamine) but not beta-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 Ca2+ homeostasis is modulated by alpha-adrenoceptor-linked pathways in these two fish species as has been previously demonstrated for the rat.