Neuromodulator role of zinc and copper during prolonged ATP applications to P2X4 purinoceptors.

To further elucidate the modulator role of trace metals such as zinc and copper on the activity of nucleotide purinoceptors, the action of these metals was assessed during prolonged ATP applications to rat P2X(4) purinoceptors expressed in Xenopus laevis oocytes. Application of ATP for 3 min resulted in a biphasic effect; a fast transient peak was followed by a slower stable current component with similar pharmacological and biophysical characteristics. The application of 1-300 microM Cu(2+) inhibited both current components to a comparable extent; likewise, Zn(2+) facilitated to a similar degree the transient and the slower stable current components. Carnosine (Car), cysteine (Cys), histidine (His), and the metal chelator, penicillamine, prevented the inhibitory action of Cu(2+); the Zn(2+) facilitation was not prevented by neither Car nor His but by either bathophenantroline or Cys, revealing metal selectivity. While the noncompetitive Cu(2+) inhibition appears to decrease channel conductance, Zn(2+) likely increases ATP affinity independently of the activation state of the purinoceptor. These results strongly support the notion that trace metals modulate the activity of the P2X(4) purinoceptor and could become relevant during continual activity of a P2X(4) purinoceptor-containing synapse.