Assessment of a model for the opposing effects of N-ethylmaleimide on the affinity of muscarinic agonists for M2 receptors.
1. Homogenates of guinea pig right atrium (M2 receptors) were treated with N-ethylmaleimide, after which the ability of carbachol to inhibit binding of [3H]quinuclidinyl benzilate was studied. 2. At 37 degrees C, 10(-4) M and 10(-3) M, but not 10(-5) M, N-ethylmaleimide increased the affinity of carbachol for the receptor. At 2 degrees C, 10(-5) M and 10(-4) M, but not 10(-3) M, N-ethylmaleimide decreased carbachol affinity. At 2 degrees C, after the homogenate had been incubated at 37 degrees C without N-ethylmaleimide, 10(-5) M N-ethylmaleimide decreased carbachol affinity, as at 2 degrees C without preincubation, but 10(-3) M N-ethylmaleimide increased carbachol affinity, as at 37 degrees C. 10(-4) M N-ethylmaleimide was without effect. 3. The results are discussed with respect to a previously proposed model in which N-ethylmaleimide interacts with two sites, causing an increase or decrease in agonist affinity respectively.
Dawson
R M
RM
Materials Research Laboratory, Melbourne, Australia.
Poretski
M
M
D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D002217:Carbachol / Q000494:pharmacology; D004229:Dithiothreitol / Q000494:pharmacology; D005033:Ethylmaleimide / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects; D066298:In Vitro Techniques; D008954:Models, Biological; D009206:Myocardium / Q000378:metabolism; D010277:Parasympathomimetics / Q000378:metabolism*; D011813:Quinuclidinyl Benzilate / Q000378:metabolism; D011976:Receptors, Muscarinic / Q000187:drug effects* / Q000378:metabolism; D013696:Temperature
D010277:Parasympathomimetics; D011976:Receptors, Muscarinic; D011813:Quinuclidinyl Benzilate; D002217:Carbachol; D005033:Ethylmaleimide; D004229:Dithiothreitol