Specific [3H]-N-methyl scopolamine binding without cholinergic function in cultured adult skin fibroblasts

Cultured adult skin fibroblasts were studied for binding and functional evidence of muscarinic receptors in order to assess their utility as a model of cholinergic function in affective illness. Saturable, specific, high affinity binding could be demonstrated in intact cells from some cell lines with [3H]-NMS, but not [3H]-QNB, presumably because of intracellular trapping of unbound [3H]-QNB. [3H]-NMS specific binding indicated a single site with a KD of approximately 210 pM. [3H]-NMS was displaced by cholinergic agonists and antagonists with relative affinities similar to muscarinic receptors in brain. Many cell lines, however, showed no specific binding. No functional response to carbachol could be demonstrated with respect to inhibition of isoproterenol-stimulated cyclic AMP formation, stimulation of cyclic GMP formation or stimulation of phosphoinositide hydrolysis in any cell line regardless of either high or no specific [3H]-NMS binding.