M2 mediated contractions of human bladder from organ donors is associated with an increase in urothelial muscarinic receptors.
OBJECTIVE
Previous studies have shown increased density of M2 receptors in hypertrophied rat bladders that possess an M2 contractile phenotype. The aim of the current study is to determine whether human bladders with an M2 contractile phenotype also have a greater density of bladder M2 receptors.


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 M2 and M3 subtypes in isolated detrusor muscle and urothelium. In addition, pig bladder muscle and urothelial receptors were quantified for comparison.


RESULTS
In the human urothelium total, M2 and M3 muscarinic 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 M2 receptors to the contractile response, points towards a possible role of the urothelium in controlling M2 mediated contractile phenotype. In comparison between human and pig bladders, the distribution of muscarinic receptor subtypes in the muscle and urothelium are quite different.
Braverman
Alan S
AS
Department of Urology, School of Medicine, Temple University, Philadelphia, Pennsylvania, USA.
Lebed
Brett
B
Linder
Mitchell
M
Ruggieri
Michael R
MR
D000293:Adolescent; D000328:Adult; D000368:Aged; D000818:Animals; D001572:Benzofurans / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D002648:Child; D002675:Child, Preschool; D018679:Cholinergic Agonists / Q000494:pharmacology; D003959:Diamines / Q000494:pharmacology; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D008875:Middle Aged; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000294:innervation / Q000502:physiology; D010276:Parasympatholytics / Q000494:pharmacology; D011759:Pyrrolidines / Q000494:pharmacology; D043585:Receptor, Muscarinic M2 / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology*; D034421:Sus scrofa; D014019:Tissue Donors; D001743:Urinary Bladder / Q000294:innervation* / Q000502:physiology*; D019459:Urothelium / Q000294:innervation*
D001572:Benzofurans; D018679:Cholinergic Agonists; D003959:Diamines; D018727:Muscarinic Antagonists; D010276:Parasympatholytics; D011759:Pyrrolidines; D043585:Receptor, Muscarinic M2; D002217:Carbachol; C101207:darifenacin; C054938:methoctramine