title: Augmentation of alpha1-adrenoceptor-mediated contraction by warming without increased phosphorylation of myosin in rat caudal arterial smooth muscle.
abstract: We previously reported the relationship between alpha1-adrenoceptor-mediated contraction and phosphorylation of 20-kDa myosin light chain (LC20) in de-endothelialized rat caudal arterial smooth muscle at room temperature (Mita M, Walsh MP. Biochem J. 1997;327:669-674). We now describe the effect of increasing the temperature to 37 degrees C on this relationship. The EC50 value (76.6 +/- 18.2 nM) for cirazoline (alpha1-adrenergic agonist)-induced contraction of the strips at room temperature (23 degrees C) was significantly greater than that (14.5 +/- 1.9 nM) at 37 degrees C. The initial rate of the contraction to a sub-maximal concentration of cirazoline (0.3 microM) was similar at the two temperatures. However, cirazoline-induced maximal force at 37 degrees C was approximately 1.8 times that at room temperature. LC20 phosphorylation in response to cirazoline at room temperature and 37 degrees C closely matched the time courses of contraction, but values were not significantly different at the two temperatures: resting phosphorylation levels were 0.09 +/- 0.04 mol P(i)/mol LC20 at 37 degrees C and 0.22 +/- 0.06 mol P(i)/mol LC20 at room temperature; maximal cirazoline-stimulated LC20 phosphorylation levels were 0.58 +/- 0.08 mol P(i)/mol LC20 at room temperature and 0.49 +/- 0.05 mol P(i)/mol LC20 at 37 degrees C. We conclude, therefore, that the enhanced cirazoline-induced contraction at 37 degrees C is not due to increased LC20 phosphorylation.
authors.affiliation: Department of Pharmacodynamics, Meiji Pharmaceutical University, Tokyo, Japan. mitsuom@my-pharm.ac.jp
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Mita
authors.forename: Michael P
authors.initials: MP
authors.lastname: Walsh
authors.forename: Masaki
authors.initials: M
authors.lastname: Saito
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D001158:Arteries / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006358:Hot Temperature; D007093:Imidazoles / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism; D018994:Myosin Light Chains / Q000378:metabolism; D010766:Phosphorylation; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D000316:Adrenergic alpha-Agonists; D007093:Imidazoles; D018994:Myosin Light Chains; C014282:cirazoline