title: Nitric oxide relaxes circular smooth muscle of rat distal colon through RhoA/Rho-kinase independent Ca2+ desensitisation.
abstract: 1. The aim of this study in circular smooth muscle of rat distal colon was to determine whether Ca(2+) desensitisation, in addition to mechanisms lowering cytosolic free Ca(2+) concentration ([Ca(2+)](cyt)), was involved in the relaxation elicited by nitric oxide (NO). Changes in isometric tension and [Ca(2+)](cyt) were recorded simultaneously in fura-2-loaded strips. 2. In methacholine (10(-5) M)-precontracted preparations, exogenous NO (10(-4) M), adenosine 5'-triphosphate (ATP; 10(-3) M) and electrical field stimulation (EFS; 1 ms, 40 V, 4 Hz, 1 min) induced a decrease in smooth muscle tension, which was accompanied by a fall in [Ca(2+)](cyt). 3. The sarcoplasmic/endoplasmic reticulum Ca(2+) ATP-ase (SERCA) inhibitor thapsigargin (10(-6) M) did not exert an influence on the decrease in tension produced by exogenous NO, but significantly attenuated the fall in [Ca(2+)](cyt). Both the relaxation and the fall in [Ca(2+)](cyt) to ATP and EFS were unaffected by thapsigargin. 4. Calyculin-A (10(-6) M), a myosin light chain phosphatase (MLCP) inhibitor, significantly reduced the decrease in tension elicited by exogenous NO, but did not alter the fall in [Ca(2+)](cyt) to exogenous NO. Inactivating RhoA by exoenzyme C3 (2 mug ml(-1)) or inhibiting Rho-kinase with (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexanecarboxamide dihydrochloride monohydrate (Y-27632; 10(-5) M) had no effect on the decrease of both tension and [Ca(2+)](cyt) generated by exogenous NO. 5. This paper demonstrates that a RhoA/Rho-kinase independent Ca(2+) desensitisation pathway contributes to the relaxation by NO in circular smooth muscle strips of rat distal colon.
authors.affiliation: Heymans Institute of Pharmacology, Ghent University, De Pintelaan 185, B-9000, Ghent, Belgium.
authors.forename: Erwin E
authors.initials: EE
authors.lastname: Colpaert
authors.forename: Adnan
authors.initials: A
authors.lastname: Levent
authors.forename: Romain A
authors.initials: RA
authors.lastname: Lefebvre
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003106:Colon / Q000201:enzymology / Q000378:metabolism / Q000502:physiology; D004558:Electric Stimulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000201:enzymology / Q000378:metabolism / Q000502:physiology; D009569:Nitric Oxide / Q000494:pharmacology / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D054460:rho-Associated Kinases
chemical_list: D004791:Enzyme Inhibitors; D047908:Intracellular Signaling Peptides and Proteins; D009569:Nitric Oxide; D000255:Adenosine Triphosphate; D017346:Protein Serine-Threonine Kinases; D054460:rho-Associated Kinases; D002118:Calcium