Intact human lymphocyte membranes respond to muscarinic receptor stimulation by oxotremorine with marked changes in microviscosity and an increase in cyclic GMP

The muscarinic agonist oxotremorine produced a linear dose-dependent increase in membrane fluidity of intact and viable human lymphocytes in vitro. This effect proved to be receptor-mediated because preincubation with 10 −5 M atropine shifted the dose-response curve one order of magnitude rightward. Pirenzepine preincubation did not affect membrane fluidity variation. A cGMP increase was also found after oxotremorine treatment. The results are discussed in terms of possible modulation ofguanyl cyclase and adenyl cyclase through membrane fluidity variations.