title: Beta-adrenergic effects on transmembrane 45Ca fluxes in isolated smooth muscle cells.
abstract: The effect of the beta-adrenergic agent isoproterenol (ISO) on transmembrane fluxes of 45Ca was assessed in smooth muscle cells in suspension. Exposure of the cells to this smooth muscle relaxant provoked a large (13-fold) transient increase in 45Ca efflux from the isolated cells. This effect was blocked by the beta-adrenergic antagonist pindolol and mimicked by exposure of the cells to dibutyryl adenosine 3',5'-cyclic monophosphate. ISO had no significant effect on 45Ca binding or on 45Ca influx in those cells, thus the ISO-induced increase in 45Ca efflux appears to reflect increased Ca2+ extrusion from the smooth muscle cells. Because the ISO-induced increase in 45Ca efflux was abolished by pretreatment of the cells with the Na+-K+ pump inhibitor ouabain and by lowering extracellular Na+ levels, we propose that the increased Ca2+ extrusion in response to ISO is coupled to increased activity of the plasmalemmal Na+-K+ pump via increased Na+-Ca2+ exchange.
mesh_terms: D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D003994:Bucladesine / Q000494:pharmacology; D002024:Bufo marinus; D002118:Calcium / Q000378:metabolism*; D002132:Calcium Radioisotopes; D002462:Cell Membrane / Q000378:metabolism; D005753:Gastric Mucosa / Q000378:metabolism; D007545:Isoproterenol / Q000494:pharmacology*; D007700:Kinetics; D008433:Mathematics; D008954:Models, Biological; D009130:Muscle, Smooth / Q000378:metabolism*
chemical_list: D002132:Calcium Radioisotopes; D003994:Bucladesine; D007545:Isoproterenol; D002118:Calcium