title: Calcium sensitization in human esophageal muscle: role for RhoA kinase in maintenance of lower esophageal sphincter tone.
abstract: A rise in intracellular-free calcium ([Ca(2+)](i)) concentration is important for initiating contraction of smooth muscles, and Ca(2+) sensitization involving RhoA kinase can sustain tension. We previously found that [Ca(2+)](i) was comparable in cells from the esophageal body (EB) and lower esophageal sphincter (LES) muscles, despite the fact that the LES maintains resting tone. We hypothesized that Ca(2+) sensitization contributes to contraction in human esophageal muscle. Tension and [Ca(2+)](i) were measured simultaneously in intact human EB and LES muscles using the ratiometric Ca(2+)-sensitive dye fura-2. Spontaneous oscillations in EB muscle tension were associated with transient elevations of [Ca(2+)](i). Carbachol caused a large increase in tension, compared with spontaneous oscillations, although the rise of [Ca(2+)](i) was similar, suggesting Ca(2+) sensitization. The RhoA-kinase blockers (R)-(+)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexanecarboxamide dihydrochloride monohydrate (Y-27632) and 1-(5-isoquinolinesulfonyl)-homopiperazine hydrochloride (HA-1077) reduced carbachol- and nerve-evoked contraction of the EB, accompanied by smaller reduction in the rise of [Ca(2+)](i). Protein kinase C inhibitors reduced force to a lesser extent. RhoA-kinase blockers caused concentration-dependent reduction of tension in spontaneously contracted LES muscles. Moreover, RhoA-kinase blockers reduced intrinsic nerve-evoked and carbachol-evoked contraction. However, there was no effect on nerve- or nitric oxide-mediated relaxation of LES. Ca(2+) sensitization mediated by the RhoA-kinase pathway has an important role in contraction of human EB muscles and LES tonic contraction, a feature not previously recognized.
authors.affiliation: Department of Physiology and Pharmacology, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, Ontario, Canada N6A 5C1. stephen.sims@schulich.uwo.ca
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Sims
authors.forename: Tom
authors.initials: T
authors.lastname: Chrones
authors.forename: Harold G
authors.initials: HG
authors.lastname: Preiksaitis
mesh_terms: D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000031:analogs & derivatives / Q000494:pharmacology; D000577:Amides / Q000494:pharmacology; D053119:Benzophenanthridines / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D004558:Electric Stimulation; D049630:Esophageal Sphincter, Lower / Q000502:physiology*; D006801:Humans; D066298:In Vitro Techniques; D009119:Muscle Contraction; D009281:Naphthalenes / Q000494:pharmacology; D011493:Protein Kinase C / Q000502:physiology; D011725:Pyridines / Q000494:pharmacology; D020742:rhoA GTP-Binding Protein / Q000037:antagonists & inhibitors / Q000502:physiology*
chemical_list: D000577:Amides; D053119:Benzophenanthridines; D009281:Naphthalenes; D011725:Pyridines; C061465:calphostin complex; C108830:Y 27632; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; C016299:chelerythrine; D011493:Protein Kinase C; D020742:rhoA GTP-Binding Protein; C049347:fasudil; D002118:Calcium