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Adrenergic responses during normoxia and chemical anoxia were investigated in anoxia-tolerant hepatocytes from the goldfish, Carassius auratus. Epinephrine-stimulated glucose release was unaltered after 1 hr of chemical anoxia, the concentration of epinephrine required for half maximal stimulation of glucose release (K0.5^GLU) ranging from 0.62 × 10^–8 to 2.05 × 10^–8 M. Similarly, the maximum rate of glucose release caused by hormonal stimulation was not affected by chemical anoxia. In anoxic goldfish hepatocytes [Ca²⁺]i remained constant in nonstimulated cells but could be elevated by addition of epinephrine. The magnitude of this [Ca²⁺]i-increase was dependent on the concentration of the catecholamine and this dependency was similar under normoxia (K0.5^Ca2+ = 1.17 × 10^–8 M) and chemical anoxia (K0.5^Ca2+ = 1.15 × 10^–8 M), as was the percentage of cells responding (77%) and displaying oscillatory [Ca²⁺]i response patterns (60%) after epinephrine addition, although the frequency of [Ca²⁺]i oscillations was significantly lower in anoxic cells. To analyze a possible shift in the importance of α- and β-adrenoceptors during chemical anoxia, the effect of phentolamine and propranolol, α- and β-adrenergic antagonists respectively, on epinephrine-stimulated glucose release was studied. Application of the α-antagonist caused a dose-dependent reduction of glucose-release which was similar under both conditions, whereas the sensitivity to the β-antagonist was lowered after chemical anoxia. Taken together these results provide evidence that during chemical anoxia goldfish hepatocytes remain responsive to adrenergic stimulation and that there is a partial shift regarding the contribution of α- and β-adrenergic pathways to the induction of cellular glucose release stimulated by epinephrine. J. Exp. Zool. 292:468–476, 2002. © 2002 Wiley-Liss, Inc.

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.