title: Calcium-dependent and calcium-independent inhibition of contraction by cGMP/cGKI in intestinal smooth muscle.
abstract: cGMP-dependent protein kinase I (cGKI) induces relaxation of smooth muscle via several pathways that include inhibition of intracellular Ca(2+) signaling and/or involve activation of myosin phosphatase. In the present study, we investigated these mechanisms comparatively in colon and jejunum longitudinal smooth muscle from mice. In simultaneous recordings from colon muscle, 8-bromo-cGMP (8-Br-cGMP) reduced both carbachol-induced tension and carbachol-induced increase in intracellular Ca(2+) concentration ([Ca(2+)](i)). These effects of 8-Br-cGMP were absent in colon from mice carrying a mutated inositol-1,4,5 trisphosphate receptor I-associated G kinase substrate (IRAG) gene or lacking cGKI. However, in jejunum, 8-Br-cGMP reduced carbachol-induced tension but did not change corresponding [Ca(2+)](i) signals. This setting was also observed in jejunum from mice carrying a mutated IRAG gene, whereas no response to 8-Br-cGMP was observed in jejunum from mice lacking cGKI. After inhibition of phosphatase activity by calyculin A, 8-Br-cGMP did not relax jejunum but still relaxed colon muscle. In Western blot analysis, 8-Br-cGMP reduced the signal for phosphorylated MYPT-1 in carbachol-stimulated jejunum but not in colon. These results suggest that cGMP/cGKI signaling differentially inhibits contraction in the muscles investigated: in jejunum, inhibition is performed without changing [Ca(2+)](i) and is dependent on phosphatase activity, whereas in colon, inhibition is mediated by inhibition of [Ca(2+)](i) signals.
authors.affiliation: Institut für Pharmakologie und Toxikologie, Technische Universität München, Munich, Germany.
authors.forename: Eva
authors.initials: E
authors.lastname: Frei
authors.forename: Maria
authors.initials: M
authors.lastname: Huster
authors.forename: Petra
authors.initials: P
authors.lastname: Smital
authors.forename: Jens
authors.initials: J
authors.lastname: Schlossmann
authors.forename: Franz
authors.initials: F
authors.lastname: Hofmann
authors.forename: Jörg W
authors.initials: JW
authors.lastname: Wegener
mesh_terms: D000577:Amides / Q000494:pharmacology; D000818:Animals; D020013:Calcium Signaling / Q000187:drug effects; D002217:Carbachol / Q000494:pharmacology; D018679:Cholinergic Agonists / Q000494:pharmacology; D003106:Colon / Q000187:drug effects / Q000201:enzymology*; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D017869:Cyclic GMP-Dependent Protein Kinases / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D007583:Jejunum / Q000187:drug effects / Q000201:enzymology*; D008387:Marine Toxins; D008565:Membrane Proteins; D051379:Mice; D018345:Mice, Knockout; D009126:Muscle Relaxation / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000201:enzymology*; D009154:Mutation; D009219:Myosin-Light-Chain Kinase / Q000378:metabolism; D043263:Myosin-Light-Chain Phosphatase; D010080:Oxazoles / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D011725:Pyridines / Q000494:pharmacology; D013997:Time Factors; D054460:rho-Associated Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D000577:Amides; D018679:Cholinergic Agonists; D004791:Enzyme Inhibitors; D008387:Marine Toxins; D008565:Membrane Proteins; C485785:Mrvi1 protein, mouse; D010080:Oxazoles; D010750:Phosphoproteins; D011725:Pyridines; C108830:Y 27632; C016276:8-bromocyclic GMP; C059041:calyculin A; D002217:Carbachol; D054460:rho-Associated Kinases; D017869:Cyclic GMP-Dependent Protein Kinases; D009219:Myosin-Light-Chain Kinase; D010749:Phosphoprotein Phosphatases; D043263:Myosin-Light-Chain Phosphatase; C510645:Ppp1r12a protein, mouse; D006152:Cyclic GMP