MUSCARINIC CHOLINERGIC RECEPTOR SUBTYPES EXPRESSION BY HUMAN PLACENTA

The presence of a cholinergic system in the placenta is suggested by s everal data, but no information is available concerning cholinergic re ceptor expression by placenta. The present study was designed to inves tigate muscarinic cholinergic receptors in sections of human placenta using a radioligand binding techniques with [H-3]N-methyl scopolamine ([H-3]NMS) as a ligand, [H-3]NMS was bound to sections of human placen ta in a manner consistent with the labelling of muscarinic cholinergic receptors. The dissociation constant (k(d)) value was 0.1 +/- 0.03 nM and the maximum density of binding site (B-max) value was 10.82 +/- 0 .09 fmol/mg of tissue. The binding was time-, temperature- and concent ration-dependent, belonging to one class of high affinity sites. Analy sis of [H-3]NMS displacement curves by compounds acting on the differe nt subtypes of muscarinic cholinergic receptor subtypes suggests that human placenta expresses the four subtypes (M(1)-M(4)) of muscarinic c holinergic receptor assayable with radioligand binding assay technique s. The demonstration of muscarinic cholinergic recognition sites in hu man placenta may contribute to define the possible significance of pla cental cholinergic system. Moreover, human placenta can be used as an easily obtainable human source of M(1)-M(4) muscarinic cholinergic rec eptor subtypes. (C) 1997 Elsevier Science Ireland Ltd.