Fig. 6.

Heterogeneous inactivation kinetics ofI_ATP in different ATP-sensitive RGCs.A, Specimen recordings ofI_ATP from four different RGCs are depicted to illustrate large differences in the decay kinetics ofI_ATP. Agonist concentration and application interval are indicated by the bars. Calibration bar applies to all four cells. In the majority of cells, the decay ofI_ATP exhibited a fast and a slow component (traces a, b, c). However, in some cells the fast component dominated the decay (trace a), whereas only the slow component was present in other RGCs (trace d).B, Superposition of the current responses illustrated inA normalized to the same peak amplitude to facilitate comparison. C, Fraction ofI_ATP remaining after 2 sec of agonist application plotted against the peak amplitude ofI_ATP. Agonist concentration was 300 μm. In a majority of RGCs,I_ATP inactivated within 2 sec to 25–60% of its peak amplitude. However, in some RGCs with relatively smallI_ATP, the fraction of remaining current was >70%. D, RGCs with slowly or noninactivating current responses showed strong attenuation ofI_ATP by the P2 receptor antagonist suramin (100 μm). Faster inactivation kinetics ofI_ATP correlated with weaker sensitivity to suramin. In both cases, I_ATP recovered almost completely after washout.