Ž . European Journal of Pharmacology 320 1997 209–214 Pharmacological characterization and distribution of muscarinic receptors in human placental syncytiotrophoblast brush-border and basal plasma membranes Jose Pavıa a, ) , Manuel Munoz b , Eugenio Jimenez b , Francisco Martos a , ´ ˜ ´ Jose Antonio Glez-Correa a , Jose Pedro De la Cruz a , Vicente Garcia a , Felipe Sanchez de la Cuesta a a Department of Pharmacology, Malaga School of Medicine, Malaga UniÕersity, 29071-Malaga, Spain b Department of Biochemistry and Molecular Biology, Malaga School of Medicine, Malaga UniÕersity, 29071-Malaga, Spain Received 5 August 1996; revised 7 November 1996; accepted 8 November 1996 Abstract Based on the existence of choline acetyltransferase and acetylcholine in human placenta, we have investigated the presence of muscarinic acetylcholine receptors in brush-border and basal plasma membranes from human term placenta. Radioligand binding assay, w 3 x Ž using H N-methyl-scopolamine as tracer, showed the existence of acetylcholine muscarinic receptors in brush-border K 0.28 "0.04 d . Ž . nM; B 9.4 "1.6 fmolrmg protein and basal plasma membranes K 0.24 "0.05 nM; B 34.3 "6.3 fmolrmg protein . In order to max d max perform a pharmacological characterization of these receptors, competition binding experiments were carried out using the muscarinic Ž Ž . . Ž . Ž receptor antagonists pirenzepine, 11 2-diethyl-amino methyl -1-piperidinylacetyl-5-11-dihydro-6 H-pyrido 14 benzodiazepine AF-DX . Ž . Ž . 116 , himbacine, 4-diphenylacetoxy-N-methylpiperidine methiodide 4-DAMP , dicyclomine and hexahydro-sila-difenidol HHSD . The results obtained showed that the muscarinic receptors in brush-border and basal plasma membranes belong to different subtypes. In Ž brush-border membranes, the receptor found match in terms of affinity for the antagonists with the muscarinic M receptor subtype K 1 i pirenzepine, 13.6 "8.2 nM; K AF-DX 116, 1680 "271 nM; K himbacine, 212 "6.5 nM; K 4-DAMP, 1.5 "0.4 nM; K i i i i . dicyclomine, 5.1 "0.8 nM; K HHSD, 34.3 "7.3 nM , whereas the receptor in basal plasma membrane seems to be of the muscarinic i Ž M receptor subtype K pirenzepine, 202 "48 nM; K AF-DX 116, 124 "60 nM; K himbacine, 20.6 "4.8 nM; K 4-DAMP, 2 i i i i . 4.5 "1.2 nM; K dicyclomine, 54.6 "22 nM; K HHSD, 89.2 "15.8 nM . The results obtained show the existence of muscarinic i i acetylcholine receptors in brush-border and basal plasma membranes from human term placenta with a different distribution pattern in terms of number of receptors and distribution of different subtypes. The functional significance of these findings is as yet unknown, but these receptors probably mediate different functions as they belong to different subtypes and are coupled to different second messengers. Ž . Keywords: Muscarinic receptor; Muscarinic receptor subtype; Placenta; Human 1. Introduction During the last two trimesters of gestation the human placenta is an organ that occupies a unique physiological position, and is able to play an important endocrine role. This organ synthesizes a large variety of hormones, such as progesterone, estradiol and estriol from precursors ob- tained from the mother or fetus which are secreted in both ) Ž . Ž . Corresponding author. Tel.: 34-52 131-569; Fax: 34-52 131-568; e-mail: Pavia@ccuma.sci.uma.es Ž maternal and fetal blood compartments Bourget et al., . 1995 . The human syncytiotrophoblast is known to serve sev- eral roles in pregnancy. It mediates the transport of nutri- ents, exchange of minerals and immunoglobulins from the maternal to fetal circulation. This polarized epithelium has a cell layer with a microvillous apical plasma membrane Ž . brush-border facing maternal blood, containing filamen- tous internal actin structure and rich in alkaline phos- phatase activity, and a smooth basal membrane facing fetal circulation rich in adenylate cyclase and Na q ,K q -ATPase activities. 0014-2999r97r$17.00 Copyright q 1997 Elsevier Science B.V. All rights reserved. Ž . PII S0014-2999 96 00889-8