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Expression of functional nicotinic acetylcholine receptors in rat urinary bladder epithelial cells

Departments of ¹Pharmacology and ²Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania

Submitted 10 March 2005 ; accepted in final form 30 August 2005

Although nicotinic acetylcholine receptors in both the central and peripheral nervous systems play a prominent role in the control of urinary bladder function, little is known regarding expression or function of nicotinic receptors in the bladder epithelium, or urothelium. Nicotinic receptors have been described in epithelial cells lining the upper gastrointestinal tract, respiratory tract, and the skin. Thus the present study examined the expression and functionality of nicotinic receptors in the urothelium, as well as the effects of stimulation of nicotinic receptors on the micturition reflex. mRNA for the ₃, ₅, ₇, ₃, and ₄ nicotinic subunits was identified in rat urothelial cells using RT-PCR. Western blotting also confirmed urothelial expression of the ₃- and ₇-subunits. Application of nicotine (50 nM) to cultured rat urothelial cells elicited an increase in intracellular Ca²⁺ concentration, indicating that at least some of the subunits form functional channels. These effects were blocked by the application of the nicotinic antagonist hexamethonium. During in vivo bladder cystometrograms in urethane-anesthetized rats, intravesical administration of nicotine, choline, or the antagonists methyllycaconitine citrate and hexamethonium elicited changes in voiding parameters. Intravesical nicotine (50 nM, 1 µM) increased the intercontraction interval. Intravesical choline (1–100 µM) also affected bladder reflexes similarly, suggesting that ₇ nicotinic receptors mediate this effect. Intravesical administration of hexamethonium (1–100 µM) potentiated the nicotine-induced changes in bladder reflexes. Methyllycaconitine citrate, a specific ₇-receptor antagonist, prevented nicotine-, choline-, and hexamethonium-induced bladder inhibition. These results are the first indication that stimulation of nonneuronal nicotinic receptors in the bladder can affect micturition.

intracellular Ca²⁺; ion channels; RT-PCR

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