Mg2+ inhibition of ATP-activated current in rat nodose ganglion neurons: evidence that Mg2+ decreases the agonist affinity of the receptor.
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 microM 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 microM in the absence of added Mg2+ to 25 microM 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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Laboratory of Molecular and Cellular Neurobiology, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, Maryland 20892-8205, USA.
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D000255:Adenosine Triphosphate / Q000502:physiology*; D000818:Animals; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology; D008274:Magnesium / Q000494:pharmacology*; D009433:Neural Inhibition / Q000187:drug effects* / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D009620:Nodose Ganglion / Q000187:drug effects* / Q000502:physiology; D018408:Patch-Clamp Techniques; D051381:Rats; D009435:Synaptic Transmission / Q000187:drug effects* / Q000502:physiology
D007473:Ion Channels; D000255:Adenosine Triphosphate; D008274:Magnesium