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Muscarinic Receptor Stimulated GTPase Activity in Synaptic Membranes from Bovine Retina
Author(s) -
McIntosh Helen,
Blazynski Christine
Publication year - 1992
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1992.tb08893.x
Subject(s) - oxotremorine , pirenzepine , methoctramine , muscarinic acetylcholine receptor , carbachol , stimulation , endocrinology , biology , chemistry , medicine , muscarinic acetylcholine receptor m1 , receptor , biochemistry
GTPase activity has been measured in synaptic membranes from bovine retina, with and without muscarinic receptor stimulation. Maximal stimulation above basal levels was achieved with 5 μM oxotremorine and 100μ M carbachol. (4‐Hydroxy‐2‐butynyl)‐1‐trimethylammonium m ‐chlorocarbanilate chloride, which is selective for the M 1 muscarinic receptor, failed to stimulate GTPase activity. 4‐Diphenylacetoxy‐ N ‐methylpiperidine methiodide (4‐DAMP) inhibition of oxotremorine stimulation demonstrated the presence of two populations of receptors, a low‐affinity site (IC 50 ±SEM, 0.63 ±0.18 μ M ) which accounted for 63% of the inhibition and a high‐affinity site (IC 50 < 1 n M ) which accounted for the remaining 37%. When carba‐chol‐stimulated GTPase activity was assayed, a single 4‐DAMP inhibitory site was apparent (IC 50 ±SEM, 2.0 ±0.9 μ M ). Pirenzepine inhibited GTPase activity at a single site (IC 50 values ±SEM, 46.9 ±11 and 25.4 ±6.5 μ M against oxotremorine and carbachol, respectively). Methoctramine was equipotent against carbachol and oxotremorine stimulation (IC 50 values, 4.2 ±1.8 and 6.2 ±1.5 μ M ). Inhibition of maximal carbachol and oxotremorine stimulation by muscarinic antagonists at the major site had a rank order of potency of 4‐DAMP = methoctramine > pirenzepine. Thus, the major site for muscarinic stimulation of GTPase activity in bovine retinal membranes is pharmacologically similar to M 2 receptors.