Abstract
In order to explore the possibility of heterogeneity in peripheral muscarine receptors, receptors were characterized in membrane fractions isolated from rabbit urinary bladder and submandibular gland. With [ 3H]QNB as radioligand, specific binding with very high affinity was found in both preparations. Although the B max S for binding in the two preparations were very similar, the mean K D value in the submandibular gland was significantly higher (< 0.005) than that in the bladder. Among the anticholinergic drugs, oxybutynin had asignificantly lower value for the inhibition constant (K i) in the submandibular gland whereas K i for both secoverine and pirenzepine was significantly higher in this tissue than in urinary bladder. The K i for carbacholine was about 7-fold higher in submandibular gland than in the bladder. Although quinidine and verapamil showed relatively weak binding to the muscarine receptor site, their K i in the submandibular gland was significantly higher than that in the bladder. The results indicate that although there is a considerable similarity between muscarinic receptors in urinary bladder and submandibular gland, the differences in K i values for different compounds in the two tissues support the argument favouring heterggeneity of muscarinic acetylcholine receptors in peripheral effector organs.
Published Version
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