M2mediated contractions of human bladder from organ donors is associated with an increase in urothelial muscarinic receptors

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Abstract
Aims: Previous studies have shown increased density of M2receptors in hypertrophied rat bladders that possess an M2contractile phenotype. The aim of the current study is to determine whether human bladders with an M2contractile phenotype also have a greater density of bladder M2receptors.Materials and Methods: Human bladders were obtained from 24 different organ transplant donors. Darifenacin and methoctramine affinity was determined by the rightward shift of cumulative carbachol concentration contractile response curves for each bladder. Radioligand binding and immunoprecipitation was used to quantify M2and M3subtypes in isolated detrusor muscle and urothelium. In addition, pig bladder muscle and urothelial receptors were quantified for comparison.Results: In the human urothelium total, M2and M3muscarinic receptor density is significantly negatively correlated with the affinity of darifenacin for inhibition of contraction of the detrusor muscle. In the detrusor muscle there is no correlation between receptor density and darifenacin affinity for inhibition of contraction. Muscarinic receptor density is greater in the muscle than in the urothelium in human bladders whereas in the pig bladder the density is greater in the urothelium than in the muscle.Conclusions: The greater density of urothelial muscarinic receptors in human bladders with lower darifenacin affinity, indicative of a greater contribution of M2receptors to the contractile response, points towards a possible role of the urothelium in controlling M2mediated contractile phenotype. In comparison between human and pig bladders, the distribution of muscarinic receptor subtypes in the muscle and urothelium are quite different. Neurourol. Urodynam.

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