title: Contracture and change in membrane potential produced by sodium removal in the dog trachea and bronchiole.
abstract: Mechanical responses and changes in membrane potential induced by Na removal were investigated in dog tracheal and bronchiolar smooth muscles. In both muscles, reduction of the external Na concentration ([Na]o) to less than 70 mM produced a sustained contracture, dose dependently. The relative amplitude of the Na-free contracture was greater than that induced by excess [K]o in the trachealis. Readmission of 1-10 mM Na, after exposure to Na-free solution, relaxed the contracture evoked by Na removal, and the degree of relaxation was dependent on [Na] readmitted. In the absence of both Na and Ca, some tension remained, and readmission of Ca increased the muscle tone. Even after pretreatment with Ca-free ethylene glycol-bis (beta-aminoethylether)-N,N,N,N'-tetraacetic acid- (0.2 mM) containing solution for 30 min, removal of Na caused some mechanical response in both muscles. D 600 (10(-7) to 10(-4) M), a blocker of voltage-dependent Ca2+ influx, suppressed the response to Na removal, but 10(-4) M D 600 did not completely block the contracture. Na removal depolarized the smooth muscle membrane to a greater extent in the bronchiole than in the trachealis. It was concluded that an increase in Ca permeability across the membrane and inhibition of the Na-Ca exchange mechanism in the absence of Na are responsible for the generation of Na-free contracture in both muscles.
authors.affiliation: Department of Pharmacology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Ito
authors.forename: T
authors.initials: T
authors.lastname: Inoue
mesh_terms: D000818:Animals; D001980:Bronchi / Q000378:metabolism*; D002118:Calcium / Q000502:physiology; D004285:Dogs; D005260:Female; D005711:Gallopamil / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D009119:Muscle Contraction; D009129:Muscle Tonus; D009130:Muscle, Smooth / Q000502:physiology*; D012964:Sodium / Q000502:physiology*; D014132:Trachea / Q000378:metabolism*
chemical_list: D005711:Gallopamil; D012964:Sodium; D002118:Calcium