title: Novel role for the transient potential receptor melastatin 4 channel in guinea pig detrusor smooth muscle physiology.
abstract: Members of the transient receptor potential (TRP) channel superfamily, including the Ca(2+)-activated monovalent cation-selective TRP melastatin 4 (TRPM4) channel, have been recently identified in the urinary bladder. However, their expression and function at the level of detrusor smooth muscle (DSM) remain largely unexplored. In this study, for the first time we investigated the role of TRPM4 channels in guinea pig DSM excitation-contraction coupling using a multidisciplinary approach encompassing protein detection, electrophysiology, live-cell Ca(2+) imaging, DSM contractility, and 9-phenanthrol, a recently characterized selective inhibitor of the TRPM4 channel. Western blot and immunocytochemistry experiments demonstrated the expression of the TRPM4 channel in whole DSM tissue and freshly isolated DSM cells with specific localization on the plasma membrane. Perforated whole cell patch-clamp recordings and real-time Ca(2+) imaging experiments with fura 2-AM, both using freshly isolated DSM cells, revealed that 9-phenanthrol (30 μM) significantly reduced the cation current and decreased intracellular Ca(2+) levels. 9-Phenanthrol (0.1-30 μM) significantly inhibited spontaneous, 0.1 μM carbachol-induced, 20 mM KCl-induced, and nerve-evoked contractions in guinea pig DSM-isolated strips with IC50 values of 1-7 μM and 70-80% maximum inhibition. 9-Phenanthrol also reduced nerve-evoked contraction amplitude induced by continuous repetitive electrical field stimulation of 10-Hz frequency and shifted the frequency-response curve (0.5-50 Hz) relative to the control. Collectively, our data demonstrate the novel finding that TRPM4 channels are expressed in guinea pig DSM and reveal their critical role in the regulation of guinea pig DSM excitation-contraction coupling.
authors.affiliation: Department of Pharmaceutical and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, SC 29208, USA.
authors.forename: Amy C
authors.initials: AC
authors.lastname: Smith
authors.forename: Kiril L
authors.initials: KL
authors.lastname: Hristov
authors.forename: Qiuping
authors.initials: Q
authors.lastname: Cheng
authors.forename: Wenkuan
authors.initials: W
authors.lastname: Xin
authors.forename: Shankar P
authors.initials: SP
authors.lastname: Parajuli
authors.forename: Scott
authors.initials: S
authors.lastname: Earley
authors.forename: John
authors.initials: J
authors.lastname: Malysz
authors.forename: Georgi V
authors.initials: GV
authors.lastname: Petkov
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D006168:Guinea Pigs; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D018408:Patch-Clamp Techniques / Q000379:methods; D010616:Phenanthrenes / Q000494:pharmacology; D050053:TRPM Cation Channels / Q000378:metabolism / Q000502:physiology*
chemical_list: D010616:Phenanthrenes; D050053:TRPM Cation Channels; C091375:9-phenanthrol; D002118:Calcium