Expression of Muscarinic M sub 3 -Receptors Coupled to Inositol Phospholipid Hydrolysis in Human Detrusor Cultured Smooth Muscle Cells

Purpose investigate the effect of muscarinic receptor agonists and antagonists on the accumulation of inositol phosphates in cultures of human detrusor smooth muscle cells. and Methods explant culture was used to derive smooth muscle cell lines from small bladder biopsies. The cells were loaded with [sup 3 H]-myoinositol, stimulated with muscarinic agonists, and the accumulation of [sup 3 H]-inositol phosphates was measured by liquid scintillation counting. (EC50 8.3 micromolar), methacholine (EC50, 7.5 micromolar), oxotremorine (EC50 2.5 micromolar) and pilocarpine (EC sub 50 8.3 micromolar) produced concentration-dependent rises in the accumulation of total [sup 3 H]-inositol phosphates. M1 (pirenzepine), M sub 2 (methoctramine) and M3 (4-DAMP and pf-HHSiD) muscarinic receptor antagonists significantly antagonized the response induced by a submaximal concentration of carbachol (100 micromolar). The apparent pA2 values were atropine (9.4), 4-DAMP (9.2), pfHHSid (7.4), pirenzepine (6.9) and methoctramine (6.3). results indicate that human detrusor smooth muscle cells in culture express M3 muscarinic receptors which are linked to phosphoinositide hydrolysis.