title: Effects of Ca2+ on force-velocity characteristics of normal and hypertrophic smooth muscle of the rat portal vein.
abstract: Portal hypertension was induced in rats by partial ligation of the hepatic branches of the portal vein. After 5 days of hypertension the portal veins were taken out and mounted for isometric and quick-release experiments. Portal veins from sham-operated normal rats served as controls. The ligated veins had an increased cross-sectional area, indicating smooth-muscle hypertrophy. Although the absolute magnitude of active force of these veins was increased, the active force per cross-sectional area was decreased, indicating an alteration in the properties of the contractile system. No difference in the Ca2+ concentration-response relations to K+-activated intact control and hypertrophic veins was found. In chemically skinned preparations, devoid of functional plasma membranes, the hypertrophic veins had similar Ca2+ sensitivity (in the presence of I microM calmodulin) but a lower force per cross-sectional area. Force-velocity relations were determined in K+-activated intact preparations. In control veins a reduction in extracellular Ca2+ was associated with a significant reduction in both isometric force and maximal shortening velocity (Vmax). In hypertrophic veins the decreased isometric force at maximal activation was associated with a low Vmax. A comparison between hypertrophic and submaximally stimulated control vessels showed corresponding Vmax and isometric force values. We conclude that the low isometric force of hypertrophic veins is associated with a lower rate of cross-bridge turnover. This could be an effect of alterations in the activation mechanisms or in the intrinsic properties of the contractile system itself.
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006975:Hypertension, Portal / Q000503:physiopathology; D006984:Hypertrophy; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000473:pathology; D011169:Portal Vein / Q000187:drug effects; D051381:Rats; D011919:Rats, Inbred Strains; D014661:Vasoconstriction / Q000187:drug effects*
chemical_list: D002118:Calcium