Muscarinic cholinergic receptors on intact human lymphocytes. Properties and subclass characterization

Saturable specific binding of tritiated N-methyl-scopolamine (3H-NMS) can be demonstrated on intact circulating human lymphocytes, with an average KD of 7 nmol/liter and an average density of about 15 fmol/10(6) cells. Specific 3H-NMS binding can be inhibited by cholinergic antagonists and agonists, is highly stereospecific for the enantiomers of the cholinergic antagonist quinuclidinyl benzilate (QNB), and is modulated by the stable guanosine triphosphate (GTP) analog GppNHp in a fashion similar to the specific binding of the same radioligand to rat heart membranes. The results indicate the presence of muscarinic cholinergic receptors on intact human lymphocytes, with a predominance of the M2 subtype. As central muscarinic cholinergic receptors have been reported to play an important role in the pathogenesis of affective disorders, the lymphocyte might represent a suitable model for the study of muscarinic receptor functions in humans.