title: Direct activation by okadaic acid of the contractile elements in the smooth muscle of guinea-pig taenia coli.
abstract: Okadaic acid isolated from black sponge (Halichondria okadai), at the concentration of 10 mumol/l, caused contraction in saponin-treated skinned smooth muscle of guinea-pig taenia coli in the absence of Ca2+. In the presence of low concentration (0.3 mumol/l) of Ca2+, okadaic acid induced a greater contraction than in the absence of Ca2+. Okadaic acid potentiated the contractions induced by Ca2+ and pCa2+-tension curve was shifted to the left as well as upward by 1 mumol/l okadaic acid. Native actomyosin preparation (myosin B) containing calmodulinmyosin light chain kinase system and phosphatase was obtained from taenia coli. Okadaic acid (10 mumol/l) increased the actomyosin Mg2+-ATPase activity in the presence or absence of Ca2+. Okadaic acid (1-100 mumol/l) had no effect on calmodulin activity as monitored by Ca2+-calmodulin activated cyclic nucleotide phosphodiesterase activity and the (Ca2+ + Mg2+)-ATPase activity or erythrocyte membranes. These results suggest that okadaic acid directly activates contractile elements of smooth muscle.
mesh_terms: D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D002118:Calcium / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D003106:Colon / Q000187:drug effects; D004910:Erythrocyte Membrane / Q000201:enzymology; D004988:Ethers, Cyclic / Q000494:pharmacology*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects* / Q000201:enzymology; D019319:Okadaic Acid; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism
chemical_list: D004988:Ethers, Cyclic; D019319:Okadaic Acid; D010727:Phosphoric Diester Hydrolases; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D002118:Calcium