Differential expression and function of nicotinic acetylcholine receptors in the urinary bladder epithelium of the rat

作者：Beckel Jonathan M^*; Birder Lori A

来源：The Journal of Physiology, 2012, 590(6): 1465-1480.

DOI：10.1113/jphysiol.2011.226860

It has been previously determined that the epithelial lining of the urinary bladder, or urothelium, expresses two subtypes of nicotinic acetylcholine receptors (nAChRs) that mediate distinct physiological effects in vivo. These effects include inhibition of bladder reflexes through alpha 7 receptors and an excitation of bladder reflexes through alpha 3-containing (alpha 3*) receptors. It is believed that urothelial receptors mediate their effects through modulating the release of neurotransmitters such as ATP that subsequently influence bladder afferent nerve excitability. Therefore, we examined the distribution of nAChRs in the urothelium, as well as their ability to influence the release of the neurotransmitter ATP. Immunofluorescent staining of both whole bladder tissue and primary urothelial cultures from the rat demonstrated that the urothelium contains both alpha 3* and alpha 7 receptors. In primary urothelial cultures, alpha 7 stimulation with choline (10 mu M to 1 mM) caused a decrease in basal ATP release while alpha 3* stimulation with cytisine (1-100 mu M) caused a concentration-dependent, biphasic response, with low concentrations (1-10 mu M) inhibiting release and higher concentrations (50-100 mu M) increasing release. These responses were mirrored in an in vitro, whole bladder preparation. In vivo, excitation of bladder reflexes in response to intravesical cytisine (100 mu M) is blocked by systemic administration of the purinergic antagonist PPADS (1 or 3 mu g kg(-1)). We also examined how each receptor subtype influenced intracellular Ca2+ levels in cultured urothelial cells. nAChR stimulation increased [Ca2+](i) through distinctmechanisms: alpha 7 through a ryanodine-sensitive intracellular mechanism and alpha 3* through extracellular influx. In addition, our findings suggest interactions between nAChR subtypes whereby activation of alpha 7 receptors inhibited the response to a subsequent activation of alpha 3* receptors, preventing the increase in [Ca2+](i) previously observed. This inhibitory effect appears to be mediated through protein kinase A- or protein kinase C-mediated pathways.

• 出版日期2012-3