Electrophysiology of T lymphocyte cholinergic receptors.

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Abstract
The presence of functional muscarinic-cholinergic receptors on at least some T lymphocytes is suggested by the existence of saturable, high-affinity, specific muscarinic binding in T cell-enriched, but not in B cell-enriched, cell suspensions and by observed cholinergic effects on lymphocytes, (e.g., increased lytic capacity of cytotoxic lymphocytes preincubated with muscarinic agents). Flow cytometry and a fluorescent probe of membrane potential, the cyanine dye 3,3''-dihexyloxacarbocyanine iodide, were used to examine the effects of cholinergic agonists and antagonists on the membrane potentials of [rat] lymphocytes in T cell-enriched and B cell-enriched suspensions. Acetylcholine (AcCho) and carbamoylcholine (CbmCho) depolarized the membranes of T cells, but not of B cells; the maximal depolarization was produced by 10 nM AcCho or by 1 nM CbmCho. Depolarization following exposure to these concentrations of agonists was maximal by 5-8 min; T cell membrane potentials returned to control values by 13-15 min. Less marked depolarization was produced by 100 nM AcCho and 10 nM CbmCho; 100 pM CbmCho was only slightly less effective than 1 nM CbmCho, and the depolarization persisted 12 min after exposure. Depolarization induced by 1 nM AcCho was abolished when AcCho was combined with 10 nM atropine but not when AcCho was combined with 1 nM atropine or 200 nM d-tubocurarine. The time course of the membrane potential response and its dependence on the relative concentrations of AcCho and specific cholinergic blocking agents correlate well with binding studies and biological effects. T lymphocytes apparently have functional muscarinic receptors; the flow cytometric method should be generally applicable to studies of the electrophysiology and pharmacology of receptor-ligand interactions.

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