Inhibition of ATP-activated current by zinc in dorsal root ganglion neurones of bullfrog
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C. Li: email@example.com
- 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.