Muscarinic receptor in house fly brain and its interaction with chlorobenzilate |
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| Authors: | Nader Shaker Amira Eldefrawi |
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| Institution: | Department of Pharmacology and Experimental Therapeutics, University of Maryland School of Medicine, Baltimore, Maryland 21201 USA |
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| Abstract: | Membranes from house fly heads were tested for the presence of mucarinic acetylcholine receptors using as a probe 3H]quinuclidinyl benzilate (3H]QNB). Based on the presence of saturable and reversible high-affinity binding of 3H]QNB, which is inhibited by muscarinic drugs, it is suggested that these sites may be muscarinic receptors. However, these putative muscarinic receptors differ in several characteristics from the ones in mammalian brain. They have lower affinities for muscarinic drugs and lower stereoselectivity, a relatively higher affinity for the nicotinic antagonist d-tubocurarine, a lower Hill coefficient for binding of muscarinic antagonists, and a lower concentration relative to α-bungarotoxin binding sites in the same membranes. Also, unlike mammalian muscarinic receptors, they are sensitive to treatments with N-ethylmaleimide and 5,5′-dithiobis(2-nitrobenzoic acid). The effect of reduction of disulfide bonds by dithiothreitol or mercaptoethanol suggests that only the insect receptor has one or more disulfide bonds which are important to binding. On the other hand, the putative muscarinic receptors of both insect and mammalian brains have important SH group(s), whose alkylation by p-chloromercuribenzoate inhibits binding. Also, chlorobenzilate is equally effective in inhibiting 3H]QNB binding to muscarinic putative receptors of house fly and bovine brains. |
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| Keywords: | To whom correspondence should be addressed |
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