Purpose: We compared the complete spectrum of receptor subtypes expressed by human detrusor and its primary culture with the expression profile in a human urothelium immortalized cell line, and in fresh urothelium tissue and its primary cell culture.
Materials and methods: The levels of mRNA expressed for receptor subtypes M1 through M5 were determined with reverse transcriptase-polymerase chain reaction and quantitative polymerase chain reaction in total RNA extracted individually from different human bladder specimens, including fresh tissue of human urothelium and detrusor, and their respective primary cultures, as well as from the UROtsa cell line.
Results: All 5 muscarinic receptors were detected in fresh human bladder tissue by reverse transcriptase-polymerase chain reaction RNA. The same was true in separated urothelium and detrusor tissue except for the lack of the M5 receptor transcript. Receptor subtype mRNA expression in the UROtsa cell line paralleled expression in fresh human bladder. Quantitative polymerase chain reaction data further corroborated these results and showed comparable mRNA expression for M2 and M3 in primary detrusor cultures. Primary cultures also had a decreased copy number of receptor genes than native tissue. The decrease was even more pronounced in primary urothelium culture and the UROtsa cell line in the presence of high calcium. M2 and M3 receptors were also detected in urothelium and detrusor by immunoreactivity.
Conclusions: We identified all 5 existing muscarinic receptor subtypes in detrusor and urothelium, and transcripts levels of M2 and M3 were comparable in detrusor. These results support an alternative site of action in urothelium for anti-muscarinic drugs. Urothelial receptors should be considered in the design of future drugs for overactive bladder.