In vitro effects of gallamine on dissociation kinetics of (3H)N-methylscopolamine and (3H)pirenzepine from rat brain muscarinic receptors

Journal of Receptor Research
M GillardJ Christophe

Abstract

Gallamine inhibited the binding of both (3H)N-Methylscopolamine ((3H)NMS) and (3H)Pirenzepine ((3H)PZ) in the hippocampus, striatum and cortex of rat brain. Competition curves between gallamine and (3H)PZ suggested that gallamine recognized an homogeneous class of receptors (Hill coefficient close to 1) whereas competition curves, using (3H)NMS as tracer, were compatible with two classes of gallamine receptors (Hill coefficient below 0.7). The latter phenomenon could be explained, at least partially, by the inhibitory effect exerted by gallamine on the k off of (3H)NMS. This effect was already observed at a 10 microM gallamine concentration and reached 100% at 1 mM (a gallamine concentration reducing the k off of (3H)PZ by 30% only). The nature of the radioligand rather than the relative abundance of M1 - M2 receptors was probably responsible for this discrepancy. Gallamine inhibited the (3H)NMS dissociation rate from brain M1 and M2 receptors (i.e. receptors with high and intermediate affinity for pirenzepine) with a lower potency than from cardiac M2 receptors (i.e. receptors with low affinity for pirenzepine).

References

Sep 3, 1984·Life Sciences·M WaelbroeckJ Christophe
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Citations

Jul 5, 1991·Biochemical Pharmacology·N H Lee, E E el-Fakahany
Jul 14, 1988·European Journal of Pharmacology·J P DehayeJ Christophe
Jul 7, 1988·European Journal of Pharmacology·F Brunner, W R Kukovetz
Sep 1, 1995·Journal of Molecular and Cellular Cardiology·M WilkinsonM Horackova
Sep 1, 1995·Toxicon : Official Journal of the International Society on Toxinology·A VandermeersE Karlsson
Oct 30, 2015·Neuropsychopharmacology : Official Publication of the American College of Neuropsychopharmacology·Brian DeanElizabeth Scarr

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