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  • Title: Effects of an alkylating derivative of oxotremorine (BM 123A) on heart rate, muscarinic receptors and adenylate cyclase activity in the rabbit myocardium.
    Author: Ehlert FJ.
    Journal: J Pharmacol Exp Ther; 1987 Jun; 241(3):804-11. PubMed ID: 3598904.
    Abstract:
    The effects of the aziridinium ion (BM 123A) of a 2-chloroethylamine derivative of oxotremorine, N-[4-(2-chloroethylmethylamino)-2-butynyl]-2-pyrrolidone (BM 123), on heart rate, muscarinic receptor binding properties and adenylate cyclase activity were investigated in the rabbit myocardium. BM 123A was a potent inhibitor of heart rate in spontaneously beating rabbit hearts. Perfusion of hearts with BM 123A for 30 min caused a lack of sensitivity of the heart to the muscarinic agonist oxotremorine-M and an 80% alkylation of muscarinic receptors as measured by the reduction in the binding capacity of N-[3H]methylscopolamine. Alkylation of muscarinic receptors in the heart with BM 123A had no significant effect on adenylate cyclase activity by itself but caused a functional blockade of muscarinic receptor-mediated inhibition of adenylate cyclase activity. The reversible binding characteristics of both BM 123 and BM 123A were investigated in competitive binding experiments with N-[3H]methylscopolamine at 0 degree C, conditions under which little or no receptor alkylation occurs. The concentration of BM 123A required for half-maximal receptor occupancy was similar to that of oxotremorine-M whereas the parent mustard (BM 123) was 200-fold less potent. GTP (10 microM) had no significant effect on the binding of N-methylscopolamine but caused a 16-fold increase in the concentration of BM 123A required for half-maximal receptor occupancy.
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