Amiloride-sensitive ion channels in urinary bladder epithelium involved in mechanosensory transduction by modulating stretch-evoked adenosine triphosphate release.

Objectives: To examine the possibility that mechanosensitive ion channels, including epithelial Na+ channels (ENaC), are implicated in mechanosensory transduction of the rat urinary bladder.

Methods: Cystometry with continuous infusion was performed to investigate the effect of intravesically perfused amiloride (a blocker of ENaC) on micturition reflex in urethane-anesthetized female rats. Bladder strips with or without epithelium suspended in organ bath were subjected to varying degrees of mechanical stretch (up to 50%). A luciferin-luciferase assay was used to quantify the change of stretch-evoked adenosine triphosphate (ATP) release by amiloride. The ENaC gene expression was assessed by reverse transcriptase-polymerase chain reaction. The expression and localization of ENaC proteins was examined using immunofluorescent staining.

Results: The intravesical perfusion of 1 mM amiloride significantly reduced the frequency of reflex voiding during bladder filling. This effect of amiloride was reversible by washing out the drug. The peak amplitude of micturition pressure was not affected by amiloride. The stretch-evoked ATP release, most of which (more than 90%) came from epithelial layer, was greatly diminished by 1 mM amiloride (from 443 to a 22% increase from basal level at 50% stretch of the original length). The alpha, beta, and gamma-ENaC subunit proteins and genes were expressed in the rat bladder epithelium.

Conclusions: The amiloride-sensitive mechanosensitive channel, including ENaC, expressed in the rat bladder epithelium might be involved in the mechanosensory transduction mechanism by controlling stretch-evoked ATP release.