Metabolic Responses to Epinephrine Stimulation in Goldfish Hepatocytes: Evidence for the Presence of α-Adrenoceptors

Abstract

The effect of epinephrine on various aspects of cellular metabolism was studied in hepatocytes from the goldfish Carassius auratus. Epinephrine increased cytosolic free calcium ([Ca2+]i) from a baseline value of 108 ± 22 nM to a peak value of 577 ± 127 nM in suspensions of hepatocytes. Responses of single cells ranged from a single spike (66% of hepatocytes) to variable oscillatory patterns (34%). The increase in [Ca2+]i was independent of the presence of extracellular Ca2+ and was prevented by the α-adrenergic antagonist phentolamine. Cellular glucose release induced by epinephrine (1.7- to 3.2-fold) was significantly reduced in Ca2+-depleted cells and in the presence of phentolamine, providing evidence for the co-occurrence of α-adrenoceptors and a Ca2+-independent, presumably β-adrenergic, system in these cells. Furthermore, epinephrine stimulated oxygen consumption in a Ca2+-dependent manner, which was not due to stimulated Na+ pump activity. An increased rate of acid secretion of 50%, evoked by epinephrine, appears to be mediated by enhanced Na+/H+ exchange but did not result in intracellular alkalization.