Mg2+Inhibition of ATP-Activated Current in Rat Nodose Ganglion Neurons: Evidence That Mg2+Decreases the Agonist Affinity of the Receptor

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Abstract
Li, Chaoying, Robert W. Peoples, and Forrest F. Weight. Mg2+inhibition of ATP-activated current in rat nodose ganglion neurons: evidence that Mg2+decreases the agonist affinity of the receptor. J. Neurophysiol. 77: 3391–3395, 1997. The effect of Mg2+on ATP-activated current in rat nodose ganglion neurons was investigated with the use of the whole cell patch-clamp technique. Mg2+decreased the amplitude of ATP-activated current in a concentration-dependent manner over the concentration range of 0.25–8 mM, with a 50% inhibitory concentration value of 1.5 mM for current activated by 10 μM ATP. Mg2+shifted the ATP concentration-response curve to the right in a parallel manner, increasing the 50% effective concentration value for ATP from 9.2 μM in the absence of added Mg2+to 25 μM in the presence of 1 mM Mg2+. Mg2+increased the deactivation rate of ATP-activated current without changing its activation rate. The observations are consistent with an action of Mg2+to inhibit ATP-gated ion channel function by decreasing the affinity of the agonist binding site on these receptors.