Identification of muscarinic receptor subtypes of cultured smooth muscle cells and tissue of human bladder body

Background: Muscarinic receptor subtypes of cultured smooth muscle cells fr om the human bladder body were investigated by the receptor binding assay m ethod. The result was compared with that obtained from the human bladder bo dy tissue to confirm whether the receptor subtypes of the cells are not cha nged after several passages of cell culture. Methods: Inhibitory effects of various muscarinic antagonists on the bindin g of [H-3]-N-methylscopolamine ([H-3]-NMS) to membrane preparations obtaine d from cultured smooth muscle cells from the fourth subculture of the human bladder body were compared with those prepared from the human bladder body tissue and cells expressing human muscarinic receptor subtypes. Results: Binding-inhibition constants (pK(i)) for atropine, pirenzepine, me thoctramine, 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP), oxyb utynin and propiverine obtained from membrane preparations of cultured smoo th muscle cells were 8.91, 6.35, 8.24, 8.53, 7.29 and 5.61, respectively. p K(i) values of these muscarinic receptor antagonists against the membrane p reparation of human bladder body tissue were 9.08, 6.66, 8.05, 8.79, 7.53 a nd 6.04, respectively. pK(i) values of cultured smooth muscle cells and tis sue from human bladder body were correlated closely with those of insect ce lls expressing the cloned human M-2 receptor subtype. Conclusion: The binding affinities for various muscarinic receptor antagoni sts of cultured human smooth muscle cells were maintained through the fourt h subculture and it was suggested that the M-2 receptor subtype is predomin antly expressed in cultured smooth muscle cells of human bladder body as we ll as in tissue of the human bladder body.