Bladder volume alters cholinergic responses of the isolated whole mouse bladder.

PURPOSE: The isolated bladder expresses autonomous activity, which may contribute to the generation of lower urinary tract sensation or pathophysiology. We evaluated how the effect of a cholinergic agonist on autonomous activity alters with increasing volume and in the presence of substances known to modulate functional bladder capacity.
MATERIALS AND METHODS: The bladder of 22 adult female C57 black mice were mounted in whole organ tissue baths. Recordings of intravesical pressure were performed under standardized conditions at different bladder volumes.
RESULTS: At low volume the muscarinic agonist arecaidine elicited an initial peak response, which subsided to a sustained steady state pressure. At high volume phasic pressure fluctuations were also apparent. An M2-receptor antagonist caused a significantly greater decrease in peak and steady state responses than in pressure fluctuations. An M3-receptor antagonist decreased all 3 components. Alpha, beta-methylene adenosine triphosphate markedly decreased fluctuations, in contrast to norepinephrine, which eliminated the steady state response while preserving fluctuations.
CONCLUSIONS: The response to cholinergic stimulation of the isolated bladder has 3 components. The initial tonic peak response increases with bladder distention and it is inhibited by M2 and M3 muscarinic receptor antagonists. The tonic steady state response does not vary with bladder volume and it is inhibited by M2 and M3-receptor antagonists, and by beta3-adrenergic receptor agonists. Phasic fluctuations are minimal at low bladder volume, and with alpha, beta-methylene adenosine triphosphate or an M3-receptor antagonist. Thus, the response to cholinergic stimulation varies with bladder volume. It can be differentially modulated by muscarinic antagonists and also by agents acting through nonmuscarinic receptors.