title: Cyclic AMP and Ca-binding in microsomal fractions isolated from rabbit colon smooth muscle.
abstract: From a homogenate of rabbit colon muscle two ATP dependent Ca-accumulating microsomal fractions were isolated by differential centrifugation on a sucrose density grandient at 35% and 35-45% sucrose. Adenylate cyclase and phosphodiesterase activities were found in the fractions. The Ca-accumulation and the ATPase activity of these fractions were stimulated by cyclic AMP (10(-5)M) at an ATP concentration of 0.35 mM ATP. In the presence of higher concentrations of ATP (5 mM) cyclic AMP had no effect on the Ca-binding. The higher concentration of ATP markedly increased the cyclic AMP formation in relation to the activity found at the lower concentration of ATP. Isoprenaline (2 X 10(-6)M) stimulated the Ca-accumulation in the 35-45% fraction and increased the hydrolysis of ATP. These effects were absent in the fraction isolated at 35% sucrose. In the former fraction isoprenaline also stimulated the adenylate cyclase activity at 0.35 mM but not at 5 mM ATP. Both the effect of isoprenaline on the Ca-binding and the adenylate cyclase activity were inhibited by the adrenergic beta-receptor blocking agent sotalol. In the 35-45% fraction papaverine (1 X 10(-3)M) stimulated the Ca-accumulation and inhibited the phosphodiesterase activity. It is suggested that cyclic AMP and agents which influence the cyclic AMP metabolism in the microsomes may have a regulatory role on the Ca-binding of the microsomes.
mesh_terms: D000249:Adenosine Monophosphate / Q000494:pharmacology; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D003106:Colon / Q000378:metabolism; D000242:Cyclic AMP / Q000096:biosynthesis / Q000378:metabolism* / Q000494:pharmacology; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008861:Microsomes / Q000201:enzymology / Q000378:metabolism*; D009130:Muscle, Smooth / Q000378:metabolism*; D010208:Papaverine / Q000494:pharmacology; D011817:Rabbits; D013015:Sotalol / Q000494:pharmacology
chemical_list: D000249:Adenosine Monophosphate; D013015:Sotalol; D010208:Papaverine; D000242:Cyclic AMP; D000251:Adenosine Triphosphatases; D007545:Isoproterenol; D002118:Calcium