Fig. 1.

ATP-induced ion currents in retinal neurons have a P2 purinergic pharmacology. A–C, Whole-cell current responses to fast-flow agonist application obtained from four different neurons (V_h = −70 mV). In each experiment, agonist application was followed by a washout period of at least 2 min.Bars indicate application intervals. Agonist concentrations are given above each bar. A, Sequential application of the P2 receptor agonists ATP and ADP elicited rapid conductance changes in retinal neurons. Note that despite higher agonist concentration, ADP-induced currents were smaller thanI_ATP. B, Current responses to ATP but not adenosine in another neuron. Agonist pulses of a fixed concentration of ATP (100 μm) and two different concentrations of adenosine (100 μm and 1 mm) were sequentially applied at an interval of 120 sec.I_ATP gradually declined on repeated application of ATP. C, I_ATPwas partially antagonized by co-application of the P2 receptor antagonist suramin (C₁, 10 μm;C₂, 100 μm). The blocking action of suramin was reversible at both concentrations as indicated by the nearly complete recovery of I_ATP. Recordings were obtained from acutely isolated RGCs. D, High-speed agonist application (300 μm ATP) revealed rapid activation time course of I_ATP followed by slow inactivation. A rapidly inactivating current component was not observed. E, Mean amplitudes ofI_ATP induced by application of saturating concentrations (300 μm) plotted against DIV. Number of tested ATP-sensitive cells at the given DIV is given inparentheses. I_ATP increased approximately fourfold from DIV 2 to 10.