title: Involvement of Ca2+ channels in endothelin-1-induced MAP kinase phosphorylation, myosin light chain phosphorylation and contraction in rabbit iris sphincter smooth muscle.
abstract: The purpose of the present study was to investigate the role and type of Ca2+ channels involved in the stimulatory effects of endothelin-1 (ET-1) on the Ca2+-dependent functional responses, p42/p44 MAP kinase phosphorylation, 20-kDa myosin light chain (MLC) phosphorylation and contraction, in rabbit iris sphincter, a nonvascular smooth muscle. ET-1 induced inositol phosphates production, MAP kinase phosphorylation, MLC phosphorylation (MLC20-P plus MLC20-2P) and contraction in a concentration-dependent manner with EC50 values of 71, 8, 6 and 25 nM, respectively. ET-1-induced MAP kinase phosphorylation, MLC phosphorylation and contraction were not significantly affected by nifedipine (1-60 microM), an L-type Ca2+ channel blocker, or by LOE 908 (1-100 microM), a blocker of Ca2+-permeable nonselective cation channels. However, SKF96365, a receptor-operated Ca2+ channel (ROCC) blocker, inhibited MAP kinase phosphorylation, MLC phosphorylation and contraction in a concentration-dependent manner with IC50 values of 28, 30 and 42 microM, respectively. 2-APB, a store-operated Ca2+ channel (SOCC) blocker, inhibited ET-1-induced MLC phosphorylation and contraction in a concentration-dependent manner with IC50 values of 12.7 and 19 microM, respectively, but was without effect on MAP kinase phosphorylation. The combined effects of submaximal concentrations of SKF96365 and 2-APB on ET-1-induced MLC phosphorylation and contraction were not additive, implying that their inhibitory actions could be mediated through a common Ca2+ entry channel. PD98059, a MAP kinase inhibitor, had no effect on ET-1-induced MLC phosphorylation and contraction, suggesting that these ET-1 effects in the rabbit iris muscle are MAP kinase-independent. In conclusion, the present study demonstrated for the first time that in rabbit iris sphincter (a) ET-1, through the ETA receptor, stimulates MAP kinase phosphorylation, MLC phosphorylation and contraction in a concentration-dependent manner, (b) that these Ca2+-dependent functional responses are not significantly affected by nifedipine or LOE908, and (c) that ET-1-induced MLC phosphorylation and contraction are inhibited by SKF96365 and 2-APB, suggesting that these effects are mainly due to store- and/or receptor Ca2+ entry.
authors.affiliation: Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta, GA 30912-2100, USA.
authors.forename: Habib R
authors.initials: HR
authors.lastname: Ansari
authors.forename: Ismail
authors.initials: I
authors.lastname: Kaddour-Djebbar
authors.forename: Ata A
authors.initials: AA
authors.lastname: Abdel-Latif
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism*; D019332:Endothelin-1 / Q000378:metabolism / Q000494:pharmacology*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000502:physiology; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000378:metabolism*; D009219:Myosin-Light-Chain Kinase / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011817:Rabbits; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology
chemical_list: D002121:Calcium Channel Blockers; D015220:Calcium Channels; D019332:Endothelin-1; D009219:Myosin-Light-Chain Kinase; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D002118:Calcium