A possible role of the cholinergic and purinergic receptor interaction in the regulation of the rat urinary bladder function.

The contractile activation of the upper (dome) and lower (base) parts of the urinary bladder show some differences. Cellular mechanisms that might be responsible for cholinergic effects blocking non-adrenergic non-cholinergic contractions in the base of the rat urinary bladder were investigated. Smooth muscle cells were thus freshly isolated or cultured both from the dome and the base of the rat urinary bladder and the contribution from cholinergic and purinergic pathways to their Ca(2+) homeostasis was examined. The expression of nicotinic acetylcholine (nAChR) and P2X2 purinergic receptors on the cultured cells and on tissue sections was investigated. The ATP-evoked Ca(2+) transients in rat smooth muscle cells did not show any desensitization. However, when ATP was administered together with carbamylcholine (CCh), the latter essentially prevented ATP from evoking Ca(2+) transients in smooth muscle cells from the base (suppression to 12 ± 2.5% of control, n = 57; p < 0.01), but not from the dome (99 ± 5% of control, n = 52; p > 0.05) of the rat urinary bladder. While atropine was unable to modify (6 ± 3% of control, n = 14; p < 0.05), α-bungarotoxin (118 ± 12% of control, n = 20; p > 0.05) blocked the inhibitory effects of CCh. Additionally, α7 subunits of nAChR and P2X2 purinergic receptors were identified using immunocytochemistry, immunohistochemistry, and Western blot in cultured urinary bladder smooth muscle cells, in urinary bladder sections, and in urinary bladder muscle strips, respectively, suggesting that the activation of nAChR modifies the action of ATP.