title: Ca2+ sensitization and the regulation of contractility in rat anococcygeus and retractor penis muscle.
abstract: Stimulation of the RhoA/Rho-kinase (ROK) signaling represents a key step in the maintenance of agonist-induced contraction of smooth muscle. We aimed to demonstrate Ca(2+) sensitization in rat anococcygeus and retractor penis muscles and to identify the molecular expression of major components of this pathway. Both anococcygeus and retractor penis showed a similar expression of RhoA, ROKalpha, and ROKbeta at the protein level as well as the mRNA for RhoGEFs. Cumulative addition of the ROK inhibitors H-1152 (0.001-3 microM), Y-27632 (0.01-30 microM) or HA-1077 (0.01-30 microM) caused sustained relaxations of precontracted smooth muscle strips. Ca(2+) sensitization induced by phenylephrine, norepinephrine and carbachol was markedly antagonized by all three ROK inhibitors. In addition, the contractile response to KCl-induced depolarization was highly sensitive to these ROK inhibitors. H-1152 was approximately 8-20 more potent than Y-27632 and HA-1077 to inhibit contraction. Electrical field stimulation (EFS, 1-32 Hz) caused transient contractions in both anococcygeus and retractor penis muscle, which were blocked by tetrodotoxin (1 microM), phentolamine (1 microM) or bretylium tosylate (30 microM). Similarly, H-1152 (0.1-1 microM), Y-27632 (1-10 microM) or HA-1077 (1-10 microM) significantly reduced EFS-evoked contractions in a concentration-dependent manner. The results indicate that the RhoA/ROK-mediated Ca(2+) sensitization pathway is expressed in anococcygeus and retractor penis muscles and enhances contractions produced by receptor-dependent and independent mechanisms.
authors.affiliation: Department of Physiology, Medical College of Georgia, Augusta, GA 30912-3000, USA. cteixeira@mail.mcg.edu <cteixeira@mail.mcg.edu>
authors.forename: Cleber E
authors.initials: CE
authors.lastname: Teixeira
authors.forename: Liming
authors.initials: L
authors.lastname: Jin
authors.forename: Zhekang
authors.initials: Z
authors.lastname: Ying
authors.forename: Trenis
authors.initials: T
authors.lastname: Palmer
authors.forename: R Clinton
authors.initials: RC
authors.lastname: Webb
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004558:Electric Stimulation; D020662:Guanine Nucleotide Exchange Factors / Q000032:analysis; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D009119:Muscle Contraction; D010413:Penis / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000032:analysis / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D064067:Rho Guanine Nucleotide Exchange Factors; D015398:Signal Transduction; D054460:rho-Associated Kinases; D020742:rhoA GTP-Binding Protein / Q000032:analysis
chemical_list: D020662:Guanine Nucleotide Exchange Factors; D047908:Intracellular Signaling Peptides and Proteins; D064067:Rho Guanine Nucleotide Exchange Factors; D017346:Protein Serine-Threonine Kinases; D054460:rho-Associated Kinases; D020742:rhoA GTP-Binding Protein; D002118:Calcium