Alpha-adrenoceptor-mediated glucose release from perifused catfish hepatocytes.
In fish liver catecholamines bind to beta-adrenoceptors (AR) and increase glucose release via cAMP augmentation. Alpha1-AR have recently been shown to mediate IP3 and Ca2+ elevation in catfish and eel hepatocytes, although their coupling to a physiological response has remained doubtful. We have perifused isolated catfish hepatocytes in Bio-Gel P4 columns with epinephrine in the presence of prazosin and/or propranolol, alpha- and beta-AR antagonists, respectively. Ten nM epinephrine stimulated glucose release approximately 3-fold, and this effect was completely antagonized by the simultaneous presence of both alpha- and beta-AR blockers. The two AR antagonists separately inhibited about one-third and two-third of the total stimulation, respectively. Through alpha-AR occupancy, epinephrine provoked a significant increase of glucose release whereas no stimulation was detected in Ca2+-depleted hepatocytes. Glucose release was strongly elevated by both ionomycin and dibutyryl cAMP. These results represent the first direct evidence that alpha-AR transduction pathway is involved in epinephrine-induced glucose release from fish hepatocytes.
Department of Biology, University of Bologna, Italy.
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Fabbri
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Buzzi
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Biondi
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Capuzzo
D018674:Adrenergic Antagonists / Q000494:pharmacology; D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002397:Catfishes; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004837:Epinephrine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism*; D066298:In Vitro Techniques; D015759:Ionomycin / Q000494:pharmacology; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011224:Prazosin / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects
D018674:Adrenergic Antagonists; D002614:Chelating Agents; D011942:Receptors, Adrenergic, alpha; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D004533:Egtazic Acid; D015759:Ionomycin; D003994:Bucladesine; D011433:Propranolol; D005947:Glucose; D002118:Calcium; D011224:Prazosin; D004837:Epinephrine