title: Vascular smooth muscle. Calmodulin and cyclic AMP-dependent protein kinase after calcium sensitivity in porcine carotid skinned fibers.
abstract: Recent work on vascular smooth muscle actomyosin has indicated that the Ca2+ sensitivity of both ATPase and superprecipitation are affected by calmodulin (CaM) and cyclic AMP-dependent protein kinase (cPK). Using a "chemically skinned" arterial preparation, we have extended these observations to the intact structured contractile system. Media from hog carotid artery were skinned with 1% Triton X-100 followed by a 50% glycerol-ATP salt solution, in which the strips were stored at -25 degrees C. Small strips (thickness between 0.1 and 0.2 mm) were mounted isometrically and relaxed in a Mg-ATP salt solution, pH 6.7, Ca2+ 10(-8) M, 30 degrees C. Ca2+ elicited a contraction with an ED50 of 10(-6) M. Isometric force was between 1 and 4 mN, consistent with the force observed before skinning. With time, the preparation became less sensitive with an increase in ED50 to 10(-5.7) M. CaM (4 micro M) reverses this loss, stabilizes the preparation, and sharply accelerates the rate of tension development. The ED50 in the presence of 4 micro M CaM shifts to about 10(-7) M. This effect is dose-dependent, with the half maximal effect at about 0.4 micro M CaM. Submaximal Ca2+ contractions can be reversibly depressed by preincubation of relaxed fibers with cPK catalytic subunit (300 U/ml), even in the presence of 4 micro M CaM. An inhibition of about 50% of the contraction at 0.2 micro M Ca2+ was obtained, whereas only 20% inhibition was found at 6 micro M Ca2+. Our findings suggest that changes in vascular contractility cannot be described solely in terms of changes in cytoplasmic Ca2+, and that changes in the sensitivity of the contractile protein to a given Ca2+ concentration are also potential mechanisms for vasodilation.
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000494:pharmacology*; D002147:Calmodulin / Q000494:pharmacology*; D002339:Carotid Arteries / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism*; D004533:Egtazic Acid / Q000494:pharmacology; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D011494:Protein Kinases / Q000494:pharmacology*; D013552:Swine
chemical_list: D002135:Calcium-Binding Proteins; D002147:Calmodulin; D004533:Egtazic Acid; D000242:Cyclic AMP; D011494:Protein Kinases; D002118:Calcium