Involvement of transient receptor potential melastatin 4 channels in the resting membrane potential setting and cholinergic contractile responses in mouse detrusor and ileal smooth muscles

Abstract

Here, we investigated the effects of 9-hydroxyphenanthrene (9-phenanthrol), a potent and selective transient receptor potential melastatin 4 (TRPM4) channel blocker, on the resting membrane potential and cholinergic contractile responses to elucidate the functional role of TRPM4 channels in the contractile activities of mouse detrusor and ileal longitudinal smooth muscles. We observed that, 9-phenanthrol (3–30 µ M) did not significantly inhibit high K + -induced contractions in both preparations; however, 9-phenanthrol (10 µ M) strongly inhibited cholinergic contractions evoked by electrical field stimulation in detrusor preparations compared to inhibitions in ileal preparations. 9-Phenanthrol (10 µ M) significantly inhibited the muscarinic agonist, carbachol-induced contractile responses and slowed the maximum upstroke velocities of the contraction in detrusor preparations. However, the agent (10 µ M) did not inhibit the contractions due to intracellular Ca 2+ release evoked by carbachol, suggesting that the inhibitory effect of 9-phenanthrol may primarily be due to the inhibition of the membrane depolarization process incurred by TRPM4 channels. On the other hand, 9-phenanthrol (10 µ M) did not affect carbachol-induced contractile responses in ileal preparations. Further, 9-phenanthrol (10 µ M) significantly hyperpolarized the resting membrane potential and decreased the basal tone in both detrusor and ileal muscle preparations. Taken together, our results suggest that TRPM4 channels are constitutively active and are involved in setting of the resting membrane potential, thereby regulating the basal tone in detrusor and ileal smooth muscles. Thus, TRPM4 channels play a significant role in cholinergic signaling in detrusor, but not ileal, smooth muscles.

TRP Channels as Lower Urinary Tract Sensory Targets

“…Alom et al [82] investigated the involvement of TRPM4 channels in cholinergic contractile responses in detrusor smooth muscle preparations in mice. They found that 9-phenanthrol significantly inhibited carbachol-induced contractions but did not inhibit contractions due to intracellular Ca 2+ release evoked by the drug, suggesting that the inhibitory effect was primarily due to the inhibition of the membrane depolarization process incurred by TRPM4 channels.…”

“…Based on the positive correlation between the density of TRPM8 channels in the bladder mucosa and voiding frequency in IDO, and the increased TRPM8 expression in bladder pain patients, it was suggested that these channels were involved in the symptomatology and pathophysiology of these disorders [81,82]. TRPM8 channels have also been implicated in the bladder cooling reflex (BCR) in humans [90,91] and animals [92,93].…”

“…Several new antagonists have been described [124,125], and some of them have been tested in animals for their effects on normal LUT and in models of LUT disorders [80,82,126,127,128,129,130].…”

Study on the pathophysiological mechanism responsible for lower urinary tract symptoms associated with prostate cancer using an animal model

“…TRPV4 regulates detrusor smooth muscles by evoking cholinergic signaling. 40 It has been reported that increase in TRPV4 expression in the bladder may induce bladder hyperactivity. 41 Furthermore, Rahaman et al 42 showed TRPV4-mediated myofibroblast differentiation and fibrosis.…”

Agents in early development for treatment of bladder dysfunction – promise of drugs acting at TRP channels?

“…Animal studies have suggested that TRPM4 could be a potential therapeutic target for detrusor overactivity. In isolated guinea-pig bladder smooth muscle strips, 9-phenanthrol, a selective inhibitor of the TRPM4 channel, reduced spontaneous contractions as well as contractions elicited by carbachol, KCl, and nerve stimulation [58][59][60][61][62]. Kullmann et al [63], investigating the potential role of TRPM4 in detrusor overactivity following spinal cord transection (SCT) in mice, found that TRPM4 was upregulated in the urothelium and detrusor smooth muscle after the lesion.…”