title: Novel regulatory mechanism in human urinary bladder: central role of transient receptor potential melastatin 4 channels in detrusor smooth muscle function.
abstract: Transient receptor potential melastatin 4 (TRPM4) channels are Ca(2+)-activated nonselective cation channels that have been recently identified as regulators of detrusor smooth muscle (DSM) function in rodents. However, their expression and function in human DSM remain unexplored. We provide insights into the functional role of TRPM4 channels in human DSM under physiological conditions. We used a multidisciplinary experimental approach, including RT-PCR, Western blotting, immunohistochemistry and immunocytochemistry, patch-clamp electrophysiology, and functional studies of DSM contractility. DSM samples were obtained from patients without preoperative overactive bladder symptoms. RT-PCR detected mRNA transcripts for TRPM4 channels in human DSM whole tissue and freshly isolated single cells. Western blotting and immunohistochemistry with confocal microscopy revealed TRPM4 protein expression in human DSM. Immunocytochemistry further detected TRPM4 protein expression in DSM single cells. Patch-clamp experiments showed that 9-phenanthrol, a selective TRPM4 channel inhibitor, significantly decreased the transient inward cation currents and voltage step-induced whole cell currents in freshly isolated human DSM cells. In current-clamp mode, 9-phenanthrol hyperpolarized the human DSM cell membrane potential. Furthermore, 9-phenanthrol attenuated the spontaneous phasic, carbachol-induced and nerve-evoked contractions in human DSM isolated strips. Significant species-related differences in TRPM4 channel activity between human, rat, and guinea pig DSM were revealed, suggesting a more prominent physiological role for the TRPM4 channel in the regulation of DSM function in humans than in rodents. In conclusion, TRPM4 channels regulate human DSM excitability and contractility and are critical determinants of human urinary bladder function. Thus, TRPM4 channels could represent promising novel targets for the pharmacological or genetic control of overactive bladder.
authors.affiliation: Department of Drug Discovery and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, South Carolina; and.
authors.forename: Kiril L
authors.initials: KL
authors.lastname: Hristov
authors.affiliation: Department of Drug Discovery and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, South Carolina; and.
authors.forename: Amy C
authors.initials: AC
authors.lastname: Smith
authors.affiliation: Department of Drug Discovery and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, South Carolina; and.
authors.forename: Shankar P
authors.initials: SP
authors.lastname: Parajuli
authors.affiliation: Department of Drug Discovery and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, South Carolina; and.
authors.forename: John
authors.initials: J
authors.lastname: Malysz
authors.affiliation: Medical University of South Carolina, Charleston, South Carolina.
authors.forename: Eric S
authors.initials: ES
authors.lastname: Rovner
authors.affiliation: Department of Drug Discovery and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, South Carolina; and Medical University of South Carolina, Charleston, South Carolina petkov@cop.sc.edu.
authors.forename: Georgi V
authors.initials: GV
authors.lastname: Petkov
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D015153:Blotting, Western; D005260:Female; D006168:Guinea Pigs; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D018613:Microscopy, Confocal; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology*; D009130:Muscle, Smooth / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013045:Species Specificity; D050053:TRPM Cation Channels / Q000378:metabolism*; D001743:Urinary Bladder / Q000378:metabolism*
chemical_list: D050053:TRPM Cation Channels; C437888:TRPM4 protein, human
keywords: 9-phenanthrol; patch-clamp electrophysiology; smooth muscle; transient receptor potential channels; urinary bladder