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  • Title: Influence of N-ethylmaleimide on cholinoceptors and responses in longitudinal muscles from guinea-pig ileum.
    Author: Aronstam RS, Carrier GO.
    Journal: Br J Pharmacol; 1982 Sep; 77(1):89-95. PubMed ID: 7126999.
    Abstract:
    1 The binding of carbamylcholine to membranes prepared from the longitudinal muscle of guinea-pig ileum was determined from its inhibition of the binding of [3H]-3-quinuclidinyl benzilate. Carbamylcholine binding was resolved into high and low affinity components with apparent dissociation constants of 0.11 +/- 0.02 and 11 +/- 1 microM; 42% of the receptors displayed high affinity carbamylcholine binding. 2 Alkylation of longitudinal muscle membranes with N-ethylmaleimide increased muscarinic receptor affinity for carbamylcholine in a manner consistent with a conversion of low affinity to high affinity receptors. After exposure the muscle membrane fragments to 1 mM N-ethylmaleimide for 20 min at 35 degrees C, carbamylcholine binding was resolved into two components with apparent dissociation constants of 0.11 +/- 0.01 and 9 +/- 2 microM, with 74% of the receptors displaying the higher affinity. 3 Exposure of longitudinal membranes mounted in an organ chamber to 1 mM N-ethylmaleimide for 30s depressed isometric contractions in response to acetylcholine by 80%, while contractions induced by K+ and Ba2+ were reduced by less than 20% and 10%, respectively. Acetylcholine dose-response curves were shifted to the right while Ba2+ curves were unaffected. 4 It is suggested that N-ethylmaleimide has a selective effect on muscarinic responses in the longitudinal muscle by disrupting processes occurring after receptor occupancy but before the induction of phospholipid turnover or calcium influx in the postsynaptic membrane.
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