The Journal of Neurophysiology Vol. 77 No. 6 June 1997, pp. 3391-3395
Copyright ©1997 The American Physiological Society

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

Chaoying Li, Robert W. Peoples, and Forrest F. Weight

Laboratory of Molecular and Cellular Neurobiology, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, Maryland 20892-8205

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.

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