title: Role of intracellular Ca2+ sequestration in beta-adrenergic relaxation of a smooth muscle.
abstract: Various mechanisms have been proposed for beta-adrenergically mediated relaxation of smooth muscle. All theories suggest the involvement of cyclic AMP as a second messenger: beta-agonists stimulate adenylate cyclase which converts ATP to cyclic AMP and protein kinase, activated by cyclic AMP, is then thought to catalyse a protein phosphorylation that leads to a reduction in free Ca2+, thus effecting relaxation. How this last step is accomplished is much debated, but the following possibilities are currently considered as the mechanisms responsible for cyclic AMP-induced reduction of cytoplasmic Ca2+: activation of a Ca2+-ATPase in the plasma and/or sarcoplasmic reticulum membranes which lowers cytoplasmic [Ca2+] in a direct manner or stimulation of (Na+-K+)ATPase in the cell membrane which may indirectly effect Ca2+ extrusion. Among the hypotheses suggested, those of Ca2+ sequestration by the sarcoplasmic reticulum and of Ca2+ extrusion across the cell membrane are consistent with each other if it is assumed that both processes are effected by a cyclic AMP-sensitive Ca2+-ATPase. However, quite a different mechanism is implied by involving the Na+-K+ pump and Na+-Ca2+ exchange carrier. In this report, we present evidence that suggests intracellular Ca2+ sequestration is the mechanism involved.
mesh_terms: D012368:4-(3-Butoxy-4-methoxybenzyl)-2-imidazolidinone / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D007545:Isoproterenol / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects*; D009126:Muscle Relaxation / Q000187:drug effects*; D009130:Muscle, Smooth / Q000502:physiology*; D010042:Ouabain / Q000494:pharmacology; D011943:Receptors, Adrenergic, beta / Q000502:physiology; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
chemical_list: D011943:Receptors, Adrenergic, beta; D012368:4-(3-Butoxy-4-methoxybenzyl)-2-imidazolidinone; D010042:Ouabain; D012964:Sodium; D000242:Cyclic AMP; D000254:Sodium-Potassium-Exchanging ATPase; D007545:Isoproterenol; D002118:Calcium