The action of alpha-adrenergic agonists on plasma-membrane calcium fluxes in perfused rat liver.
The effect of alpha-adrenergic agonists on Ca2+ fluxes was examined in the perfused rat liver by using a combination of Ca2+-electrode and 45Ca2+-uptake techniques. We showed that net Ca2+ fluxes can be described by the activities of separate Ca2+-uptake and Ca2+-efflux components, and that alpha-adrenergic agonists modulate the activity of both components in a time-dependent manner. Under resting conditions, Ca2+-uptake and -efflux activities are balanced, resulting in Ca2+ cycling across the plasma membrane. The alpha-adrenergic agonists vasopressin and angiotensin, but not glucagon, stimulate the rate of both Ca2+ efflux and Ca2+ uptake. During the first 2-3 min of alpha-agonist administration the effect on the efflux component is the greater, the net effect being efflux of Ca2+ from the cell. After 3-4 min of phenylephrine treatment, net Ca2+ movements are essentially complete, however, the rate of Ca2+ cycling is significantly increased. After removal of the alpha-agonist a large stimulation of the rate of Ca2+ uptake leads to the net accumulation of Ca2+ by the cell. The potential role of these Ca2+ flux changes in the expression of alpha-adrenergic-agonist-mediated effects is discussed.
D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D005934:Glucagon / Q000494:pharmacology; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D010477:Perfusion; D010656:Phenylephrine / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D014667:Vasopressins / Q000494:pharmacology
D014667:Vasopressins; D000804:Angiotensin II; D010656:Phenylephrine; D005934:Glucagon; D002118:Calcium