Inhibition of ATP-activated current by zinc in dorsal root ganglion neurones of bullfrog

Authors

  • Chaoying Li,

    Corresponding author
    1. Laboratory of Molecular and Cellular Neurobiology, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD 20892–8115, USA
    • To whom correspondence should be addressed at the Laboratory of Molecular and Cellular Neurobiology, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, 12501 Washington Avenue, Rockville, MD 20852, USA.

    Search for more papers by this author
  • Robert W. Peoples,

    1. Laboratory of Molecular and Cellular Neurobiology, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD 20892–8115, USA
    Search for more papers by this author
  • Forrest F. Weight

    1. Laboratory of Molecular and Cellular Neurobiology, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD 20892–8115, USA
    Search for more papers by this author

Abstract

  • 1The effect of Zn2+ on ATP-activated current was studied in bullfrog dorsal root ganglion (DRG) neurones using the whole-cell patch-clamp technique.
  • 2Zn2+ (2–800 μm) inhibited current activated by submaximal concentrations of ATP. The Zn2+ concentration that produced 50% inhibition (IC50) of current activated by 2.5 μm ATP was 61 ± 9.8 μm. When ATP concentrations were adjusted to account for chelation of Zn2+, the IC50 of Zn2+ was 86 ± 18 μm.
  • 3The inhibitory action of Zn2+ on ATP-gated channels did not appear to be due to a decrease in the concentration of one or more species of ATP.
  • 4Zn2+ inhibition of ATP-activated current was independent of membrane potential between −80 and +40 mV, and did not involve a shift in the reversal potential of the current.
  • 5Zn2+ (100 μm) shifted the ATP concentration-response curve to the right in a parallel manner, increasing the EC50 for ATP from 2.5 ± 0.5 μm to 5.5 ± 0.4 μm.
  • 6Zn2+ decreased the time constant of deactivation of ATP-gated ion channels without affecting the time constant of activation or desensitization.
  • 7Dithiothreitol (DTT) reversed Zn2+ inhibition of ATP-activated current.
  • 82-Methylthio ATP, α,β-methylene ATP and ADP activated current with EC50 values of 2.4 ± 0.3, 50.1 ± 5.8 and 303.1 ± 53.9 μm, respectively. Adenosine, AMP or β,γ-methylene ATP did not evoke detectable current.
  • 9Reactive Blue 2 and pyridoxal-phosphate-6-azophenyl-2′,4′-disulphonic acid inhibited ATP-activated current.
  • 10The results suggest that Zn2+ can inhibit P2X purinoceptor function by decreasing the affinity of the binding site for ATP. These observations provide the first evidence for this action of Zn2+ on a neurotransmitter-gated ion channel. Furthermore, the receptor-channel in these neurones appears to be a novel member of the P2X purinoceptor class.

Ancillary