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

Abstract

Purpose
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\nTo investigate the effect of muscarinic receptor agonists and antagonists on the accumulation of inositol phosphates in cultures of human detrusor smooth muscle cells.
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\nMaterials and Methods
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\nPrimary 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.
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\nResults
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\nCarbachol (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).
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\nConclusions
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\nThese results indicate that human detrusor smooth muscle cells in culture express M3 muscarinic receptors which are linked to phosphoinositide hydrolysis.