Constitutive muscarinic receptors are involved in the growth and differentiation of friend erythroleukemia cells

Binding experiments with the specific muscarinic ligand [H-3]N-methylscopol amine (H-3-NMS) have shown the presence of constitutive muscarinic acetylch oline receptors (mAChR) on Friend murine erythroleukemia cells (MELC). Comp etition experiments with a panel of specific antagonists indicated that the mAChR were predominantly of the M3 subtype. This was confirmed by the rt-P CR analysis of mRNA levels for M1-M5 AChR. Uninduced MELC expressed approxi mately 2,100 and 1,200 binding sites per cell of growing and resting popula tions, respectively. The dissociation constant (K-D) for H-3-NMS was in the picomolar range. The modulation of mAChR upon induction suggested that MEL C growth and maturation might be under control of a cholinergic system sinc e mAChR were markedly decreased or virtually absent in MELC induced to term inal division by dimethyl sulfoxide (DMSO) or hexamethylene bisacetamide (H MBA), respectively. In turn, the number of mAChR on MELC committed to polyp loidization by colcemid was either increased over or maintained at the cont rol levels when receptor densities were expressed per cell or surface unit (square micrometers), respectively. Moreover, the muscarinic agonist carbac hol was round to inhibit MELC differentiation by decreasing by approximatel y 35% the amount of benzidine-positive (B+) cells in HMBA-induced cultures and, to a lesser degree, also AChE revels. The carbachol effect on erythroi d differentiation was reverted by atropine that was found to restore the or iginal amount of B+ cells, while it reduced acetylcholinesterase (AChE) to levels of approximately 66% of control. Such a selective atropine-mediated inhibition of AChE expression was observed also in HMBA-induced MELC supple mented with the antagonist. These results have suggested that mAChR on MELC are functional and might play a role in modulating the expression of eithe r the erythroid or megakaryocytic traits of these cells. J. Cell. Physiol. 178:333-340, 1999. (C) 1999 Wiley-Liss, Inc.