title: alpha1-Adrenoceptor-mediated phosphorylation of myosin in rat-tail arterial smooth muscle.
abstract: The mechanism of alpha1-adrenoceptor-mediated contraction was investigated in helical strips of the rat-tail artery. Muscle strips with the endothelium removed contracted in response to the alpha1-adrenoceptor agonist cirazoline, with half-maximal contraction at 0.23 microM. The contractile response to a submaximal concentration of cirazoline (0.3 microM) was biphasic, with a rapid phasic component peaking at approx. 30 s, followed by sustained tonic contraction. Phosphorylation of the 20 kDa light chain of myosin (LC20) in response to 0.3 microM cirazoline was also biphasic and closely matched the time-course of contraction. Resting LC20 phosphorylation levels were 0.22+/-0.06 mol of Pi/mol of LC20 (n=3) and reached a maximum of 0.58+/-0.08 mol of Pi/mol of LC20 (n=3). Phosphopeptide mapping and phosphoamino acid analysis revealed that LC20 phosphorylation occurred exclusively at serine-19. The sustained phase of contraction was eliminated by removal of extracellular Ca2+ and the phasic response was eliminated by depletion of endogenous Ca2+ stores. Both phases of the contractile response were restored by re-addition of Ca2+ to the bathing medium. LC20 phosphorylation and both phases of the contractile response to 0.3 microM cirazoline were inhibited by the myosin light-chain kinase inhibitor ML-9 (30 microM). Resting LC20 phosphorylation, however, was unaffected by ML-9. Finally, both phasic and tonic responses to 0.3 microM cirazoline were partially inhibited by chloroethylclonidine (50 microM), suggesting the involvement of both alpha1A and alpha1B adrenoceptors in these contractile responses.
authors.affiliation: Smooth Muscle Research Group and Department of Medical Biochemistry, Faculty of Medicine, University of Calgary, 3330 Hospital Drive N.W., Calgary, Alberta, Canada T2N 4N1.
authors.forename: M
authors.initials: M
authors.lastname: Mita
authors.forename: M P
authors.initials: MP
authors.lastname: Walsh
mesh_terms: D058668:Adrenergic alpha-1 Receptor Antagonists; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001158:Arteries / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D001381:Azepines / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D003000:Clonidine / Q000031:analogs & derivatives / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D018994:Myosin Light Chains / Q000737:chemistry / Q000378:metabolism*; D009219:Myosin-Light-Chain Kinase / Q000037:antagonists & inhibitors; D010766:Phosphorylation; D051381:Rats; D017207:Rats, Sprague-Dawley; D018340:Receptors, Adrenergic, alpha-1 / Q000187:drug effects / Q000502:physiology*; D012694:Serine / Q000737:chemistry; D013623:Tail / Q000098:blood supply
chemical_list: C547715:Adra1a protein, rat; C547718:Adra1b protein, rat; D058668:Adrenergic alpha-1 Receptor Antagonists; D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D001381:Azepines; D004791:Enzyme Inhibitors; D007093:Imidazoles; D018994:Myosin Light Chains; D018340:Receptors, Adrenergic, alpha-1; C056218:ML 9; C051731:chlorethylclonidine; D012694:Serine; D009219:Myosin-Light-Chain Kinase; D003000:Clonidine; C014282:cirazoline; D002118:Calcium