EXPRESSION OF MUSCARINIC M(3)-RECEPTORS COUPLED TO INOSITOL PHOSPHOLIPID HYDROLYSIS IN HUMAN DETRUSOR CULTURED SMOOTH-MUSCLE CELLS

Purpose: To investigate the effect of muscarinic receptor agonists and antagonists on the accumulation of inositol phosphates in cultures of human detrusor smooth muscle cells. Materials and Methods: Primary explant culture was used to derive smooth muscle cell lines from small bladder biopsies. The cells were loaded with [H-3]-myoinositol, stimulated with muscarinic agonists, and the accumulation of [H-3]-inositol phosphates was measured by liquid scintillation counting. Results: Carbachol (EC(50) 8.3 mu M.), methacholine (EC(50) 7.5 mu M.), oxotremorine (EC(50) 2.5 mu M.) and pilocarpine (EC(50) 8.3 mu M.) produced concentration-dependent rises in the accumulation of total [H-3]-inositol phosphates. M(1) (pirenzepine), M(2) (methoctramine) and M(3) (4-DAMP and pf-HHSiD) muscarinic receptor antagonists significantly antagonized the response induced by a submaximal concentration of carbachol (100 mu M.). The apparent pA(2) values were atropine (9.4), 4-DAMP (9.2), pfHHSid (7.4), pirenzepine (6.9) and methoctramine (6.3). Conclusions: These results indicate that human detrusor smooth muscle cells in culture express M(3) muscarinic receptors which are linked to phosphoinositide hydrolysis.