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Differential Modulation by Copper and Zinc of P 2 X 2 and P 2 X 4 Receptor Function

Keming Xiong, Robert W. Peoples, Jennifer P. Montgomery, Yisheng Chiang, Randall R. Stewart, Forrest F. Weight, and Chaoying Li. Differential Modulation by Copper and Zinc of P2X 2 and P2X4 Receptor Function. J. Neurophysiol. 81: 2088–2094, 1999. The modulation by Cu 21 and Zn of P2X2 and P2X4 receptors expressed inXenopusoocytes was studied with the two-electrode, voltage-clamp technique. In oocytes expressing P2X 2 receptors, both Cu and Zn, in the concentration range 1–130 mM, reversibly potentiated current activated by submaximal concentrations of ATP. The Cu and Zn concentrations that produced 50% of maximal potentiation (EC50) of current activated by 50mM ATP were 16.36 0.9 (SE) mM and 19.66 1.5 mM, respectively. Cu 21 and Zn potentiation of ATP-activated current was independent of membrane potential between280 and120 mV and did not involve a shift in the reversal potential of the current. Like Zn , Cu increased the apparent affinity of the receptor for ATP, as evidenced by a parallel shift of the ATP concentration-response curve to the left. However, Cu did not enhance ATP-activated current in the presence of a maximally effective concentration of Zn , suggesting a common site or mechanism of action of Cu 21 and Zn on P2X2 receptors. For the P2X4 receptor, Zn , from 0.5 to 20mM enhanced current activated by 5 mM ATP with an EC50 value of 2.46 0.2mM. Zn 21 shifted the ATP concentration-response curve to the left in a parallel manner, and potentiation by Zn was voltage independent. By contrast, Cu 21 in a similar concentration range did not affect ATP-activated current in oocytes expressing P2X 4 receptors, and Cu 21 did not alter the potentiation of ATP-activated current produced by Zn . The results suggest that Cu 21 and Zn differentially modulate the function of P2X 2 and P2X4 receptors, perhaps because of differences in a shared site of action on both subunits or the absence of a site for Cu 21 action on the P2X4 receptor.