Identification of M2 muscarinic receptors in membranes from bovine cerebral basal arteries.
Muscarinic receptors were identified in membrane preparations from bovine cerebral arteries by the specific binding of [3H]-quinuclidinyl benzilate. The total amount of binding sites is relatively high: 1.5 pmol/mg protein, as compared to 0.91 pmol/mg for bovine cerebral cortex and 0.08 pmol/mg for heart muscle. In this study we show that the majority of these sites correspond to M2-receptors: 84% of the sites display low affinity for pirenzepine. In addition, GTP causes a rightward shift and steepening of the carbachol competition binding curve. In the presence of GTP, the alkylating reagent N-ethylmaleimide causes a 28-fold increase of the affinity for carbachol. This phenomenon is also observed on bovine heart membranes where muscarinic receptors are known to be of the M2 type. In contrast, muscarinic receptors in cerebral cortex, predominantly of the M1-type, show only a 4-fold increase in agonist affinity by N-ethylmaleimide. These findings suggest that the ability of N-ethylmaleimide to modulate the agonist affinity is an additional criterion for the characterization of muscarinic M2-type receptors.
D000818:Animals; D002217:Carbachol / Q000378:metabolism; D002417:Cattle; D002536:Cerebral Arteries / Q000032:analysis*; D002540:Cerebral Cortex / Q000032:analysis; D005033:Ethylmaleimide / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000494:pharmacology; D008566:Membranes / Q000032:analysis; D009206:Myocardium / Q000032:analysis; D010890:Pirenzepine / Q000378:metabolism; D011813:Quinuclidinyl Benzilate / Q000378:metabolism; D011976:Receptors, Muscarinic / Q000378:metabolism*
D011976:Receptors, Muscarinic; D010890:Pirenzepine; D011813:Quinuclidinyl Benzilate; D006160:Guanosine Triphosphate; D002217:Carbachol; D005033:Ethylmaleimide