title: Inhibitory effect of phorbol 12,13-dibutyrate on norepinephrine-induced contraction in rabbit iris dilator muscle.
abstract: The hypothesis that the increase in Ca2+ sensitivity on norepinephrine-induced contraction of smooth muscles and also the decrease of the norepinephrine-induced sustained level of intracellular Ca2+ concentration are produced by the activation of protein kinase C was tested. Phorbol 12,13-dibutyrate (PDB; 10(-6) M) relaxed the norepinephrine-induced sustained contraction in a concentration-dependent manner. On pretreatment with PDB a transient contraction was produced by the application of norepinephrine, but the sustained contraction was significantly reduced. The sustained elevations of intracellular Ca2+ concentration ([Ca2+]i) and the contraction induced by norepinephrine in fura-2-loaded preparations were decreased by the application of PDB. These inhibitory effects were antagonized by potent protein kinase inhibitors, 2-(1-(3-dimethylaminopropyl)-indol-3-yl)-3-(-indol-3-yl)-maleimide (GF 109203X) (10 (-6) M) and 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7) (10 (-6) M), but were not affected by a protein kinase A/G inhibitor, N-(2-cinnamylaminoethyl)-5-isoquinolinesulfonamide (H-88) (10(-6) M). The slope of the regression line for norepinephrine for [Ca2+]i and tension was significantly steeper than those obtained with high K+. Also, on pretreatment with PDB the Ca2+ sensitivity of the K(+)-induced contraction was decreased, but the Ca2+ sensitivity of norepinephrine-induced contraction tended to be increased. These observations indicate that PDB induces a decrease of [Ca2+]i on Ca2+ mobility and an increase of Ca2+ sensitivity on contraction of smooth muscle through the activation of protein kinase C.
authors.affiliation: Department of Chemical Pharmacology, Toho University School of Pharmaceutical Sciences, Chiba, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Satoh
authors.forename: K
authors.initials: K
authors.lastname: Matsuo
authors.forename: N
authors.initials: N
authors.lastname: Kokubu
authors.forename: I
authors.initials: I
authors.lastname: Takayanagi
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D017275:Isradipine / Q000494:pharmacology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism; D009638:Norepinephrine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D009801:Oculomotor Muscles / Q000187:drug effects* / Q000378:metabolism; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology*; D011493:Protein Kinase C / Q000378:metabolism*; D011817:Rabbits
chemical_list: D000316:Adrenergic alpha-Agonists; D002121:Calcium Channel Blockers; D015240:Phorbol 12,13-Dibutyrate; D011493:Protein Kinase C; D002118:Calcium; D009638:Norepinephrine; D017275:Isradipine