Modulation of ATP-induced currents by zinc in acutely isolated hypothalamic neurons of the rat

Abstract

1. Whole-cell patch-clamp and fast perfusion were used to study the effects of zinc on adenosine 5′-triphosphate (ATP)-induced responses of histaminergic neurons. 2. At 10-30 μM ATP, Zn 2+ had biphasic effects on ATP responses. Zn 2+ at 3-100 μM increased the ATP-induced currents, but inhibited them at higher concentrations. 3. At 300 μM ATP, Zn 2+ predominantly but incompletely inhibited the currents. 4. At 5 and 50 μM, Zn 2+ shifted to the left the concentration-response curve for ATP-induced currents, without changing the maximal response. At 1 mM, Zn 2+ inhibited ATP-induced currents in a noncompetitive way, reducing the maximal response by 58%. 5. Zn 2+ increased the decay time of ATP-evoked currents nine fold with an EC 50 of 63 μM. Upon removal of high concentrations of Zn 2+, there was a rapid increase of the current followed by a slow decline towards the response amplitude seen with ATP alone. The appearance of a tail current is consistent with a Zn 2+-induced increase of ATP affinity and an inhibition of its efficacy. 6. Thus, Zn 2+ acts as a bidirectional modulator of ATP receptor channels in tuberomamillary neurons, which possess functional P2X 2 receptors. The data are consistent with the existence of two distinct modulatory sites on the P2X receptor, which can be occupied by Zn 2+. 7. Our data suggest that zinc-induced potentiation of ATP-mediated currents is caused by the slowing of ATP dissociation from the receptor, while inhibition of ATP-induced currents is related to the suppression of ATP receptor gating.