The TRPM4 channel is a Ca2+-activated, monovalent cation selective channel of the melastatin transient receptor potential (TRPM) family. TRPM4 channel is implicated in the regulation of many cellular processes including the immune response, insulin secretion, and pressure-induced vasoconstriction of cerebral arteries. However, the expression and function of the TRPM4 channels in detrusor smooth muscle (DSM) has not yet been explored. Here, we provide the first molecular, electrophysiological, and functional evidence for the presence of the TRPM4 channels in rat DSM. We detected the expression of the TRPM4 channels at mRNA and protein levels in freshly isolated DSM single cells and DSM tissue using reverse transcription-polymerase chain reaction, Western blot, immunohistochemistry and immunocytochemistry. 9-hydroxyphenanthrene (9-phenanthrol), a novel selective inhibitor of the TRPM4 channels, was used to examine their role in DSM function. In perforated patch-clamp recordings using freshly isolated rat DSM cells, 9-phenanthrol (30 μM) decreased the spontaneous inward current activity at -70 mV. Real-time DSM live-cell Ca2+ imaging showed that selective inhibition of TRPM4 channel with 9-phenanthrol (30 μM) significantly reduced the intracellular Ca2+ levels. Isometric DSM tension recordings revealed that 9-phenanthrol (0.1-30 μM) significantly inhibited the amplitude, muscle force integral, and frequency of the spontaneous phasic and pharmacologically induced contractions of rat DSM isolated strips. 9-phenanthrol also decreased the amplitude and muscle force integral of electrical field stimulation-induced contractions. In conclusion, this is the first study to examine the expression and provide evidence for the TRPM4 channels as critical regulators of rat DSM excitability and contractility.
- detrusor smooth muscle
- Copyright © 2012, American Journal of Physiology - Renal Physiology