Alpha-mediated changes in hepatocyte intracellular calcium in the catfish, Ictalurus melas.
Adult catfish, Ictalurus melas, hepatocytes respond to alpha-agonists by increasing intracellular free calcium concentrations ([Ca2+]i) in a dose-dependent manner. Basal [Ca2+]i were approximately 78 nM in catfish hepatocytes; this value was increased by 213, 243, 131, and 238 nM in the presence of epinephrine (Epi; 10(-6) M), norepinephrine (NE; 10(-5) M), phenylephrine (PE; 10(-4) M), and isoproterenol (Iso; 10(-4) M), respectively. The binding constants were 3.4 x 10(-8), 2.6 x 10(-7), 9.8 x 10(-7), and 6.1 x 10(-5) M for Epi, NE, PE, and Iso, respectively, which is the same order of potency for these agonists reported for the alpha 1-adrenoceptor system of mammalian hepatocytes. The Epi-induced changes in [Ca2+]i were antagonized equally by phentolamine (PH; 10(-8) M) and yohimbine (10(-8) M) but poorly by propranolol (Prop; 10(-6) M), as indicated by their respective inhibitory constants. Epi (10(-7) M) induced a time-dependent increase in hepatocyte adenosine 3',5'-cyclic monophosphate concentration that was antagonized by Prop but not PH. There were, however, no clear agonist-induced changes in the activities of glycogen phosphorylase (total, a, or %a) under these conditions. These studies provide evidence that Epi and other adrenergic agonists increase [Ca2+]i by an alpha- or alpha 1-like adrenoceptor pathway in catfish hepatocytes, but the biochemical effector system responding to changes in [Ca2+]i has yet to be elucidated.
Moon
T W
TW
Institute of General Physiology, University of Ferrara, Italy.
Capuzzo
A
A
Puviani
A C
AC
Ottolenghi
C
C
Fabbri
E
E
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004837:Epinephrine / Q000378:metabolism / Q000494:pharmacology; D007059:Ictaluridae; D007545:Isoproterenol / Q000378:metabolism / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D009638:Norepinephrine / Q000378:metabolism / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D010656:Phenylephrine / Q000378:metabolism / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*; D015016:Yohimbine / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D015016:Yohimbine; D011433:Propranolol; D000242:Cyclic AMP; D007545:Isoproterenol; D002118:Calcium; D009638:Norepinephrine; D004837:Epinephrine; D010646:Phentolamine