Journal of Neuroscience, Vol 5, 1202-1207, Copyright © 1985 by Society for Neuroscience
Pharmacological and ionic characterizations of the muscarinic receptors modulating [3H]acetylcholine release from rat cortical synaptosomes
EM Meyer and DH Otero
The muscarinic receptors that modulate acetylcholine release from rat
cortical synaptosomes were characterized with respect to sensitivity to
drugs that act selectively at M1 or M2 receptor subtypes, as well as to
changes in ionic strength and membrane potential. The modulatory receptors
appear to be of the M2 type, since they are activated by carbachol,
acetylcholine, methacholine, oxotremorine, and bethanechol, but not by
pilocarpine, and are blocked by atropine, scopolamine, and gallamine (at
high concentrations), but not by pirenzepine or dicyclomine. The ED50S for
carbachol, acetylcholine, and oxotremorine are less than 10 microM,
suggesting that the high affinity state of the receptor is functional. High
ionic strength induced by raising the NaCl concentration has no effect on
agonist (oxotremorine) potency, but increases the efficacy of this
compound, which disagrees with receptor- binding studies. On the other
hand, depolarization with either KCl or with veratridine (20 microM)
reduces agonist potencies by approximately an order of magnitude,
suggesting a potential mechanism for receptor regulation.