Interstitial cells and cholinergic signalling in the outer muscle layers of the guinea-pig bladder

To explore the relationship between cholinergic mechanisms and interstitial cells (ICs) in the outer muscle layer of the bladder.

In bladder tissue from male guinea-pigs, ICs were identified by their response to nitric oxide (NO) with a rise in cGMP. Sections of the lateral bladder wall were incubated in Krebs' solution containing 1 mm of the nonspecific phosphodiesterase inhibitor isobutyl-methyl-xanthene. Tissues were then exposed to 100 microm of the NO donor NONOate for 10 min, control tissues remained in Krebs' solution. Tissues were then processed for immunohistochemistry for cGMP, choline acetyltransferase (ChAT), neurofilament protein, and the nonspecific neuronal marker protein gene product (PGP) 9.5.

cGMP-positive ICs were found mainly in the outer muscle layers of the bladder wall. Three types were identified based on location; on the outer surface of the bladder wall, on the surface of the muscle bundles, and within the muscle bundles. Some of the intramuscular ICs stained for ChAT, but they did not stain with PGP 9.5. Nerve fibres were seen in close contact with the ChAT-positive intramuscular ICs, and these nerves expressed ChAT and neurofilament protein.

A subpopulation of intramuscular ICs can synthesise acetylcholine, and might release acetylcholine onto the underlying muscle. These cells are in close contact with nerves, suggesting that they might be activated by neural inputs. Thus there may be a system in the detrusor involving cholinergic nerves acting on ICs which can activate the smooth muscle via a complex cholinergic input.