title: Glucagon-stimulated calcium efflux in the isolated perfused rat liver is dependent on cellular redox potential.
abstract: In the absence of any exogenous substrates, glucagon (1 X 10(-9) M) stimulated 45Ca2+ efflux from perfused livers derived from fed rats but not in livers of 24-h-fasted animals. In livers of 24-h-fasted animals perfused under conditions which would decrease cellular NAD(P)H/NAD(P)+ ratio (pyruvate (2.0 mM) or acetoacetate (10.0 mM], glucagon (1 X 10(-9) M) did not stimulate 45Ca2+ efflux. Similarly, in livers of 24-h-fasted animals perfused with substrates which increase cellular NAD(P)H content (lactate (2.0 mM) or beta-hydroxybutyrate (10.0 mM], glucagon (1 X 10(-9) M) did not increase 45Ca2+ efflux. Glucagon (1 X 10(-9) M) elicited an increase in 45Ca2+ efflux from livers of 24-h-fasted animals, only when the livers were perfused with [lactate]/[pyruvate] and [beta-hydroxybutyrate]/[acetoacetate] ratios similar to those reported for livers of fed rats. Stimulation of 45Ca2+ efflux elicited by either 8-CPT-cAMP, a cAMP analog, or high glucagon concentrations (1 X 10(-8) M) was not affected whether livers were perfused with pyruvate (2.0 mM) or lactate (2.0 mM). Administration of isobutylmethylxanthine (50 microM) alone, or glucagon (1 X 10(-9) M) in the presence of isobutylmethylxanthine (50 microM) stimulated 45Ca2+ efflux from livers of 24-h-fasted animals perfused with pyruvate (2.0 mM) but not from livers perfused with lactate (2.0 mM). The ability of glucagon (1 X 10(-9) M) to elevate tissue cAMP levels was also regulated by the oxidation-reduction state of the livers. The data indicate that glucagon-stimulated 45Ca2+ efflux from perfused livers is mediated via cAMP and is dependent on the oxidation-reduction state of the livers.
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D005215:Fasting; D005934:Glucagon / Q000494:pharmacology*; D066298:In Vitro Techniques; D007657:Ketone Bodies / Q000494:pharmacology; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction; D010477:Perfusion; D010656:Phenylephrine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values
chemical_list: D007657:Ketone Bodies; D009243:NAD; D010656:Phenylephrine; D009249:NADP; D005934:Glucagon; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine