Recovery components of fish cone photoresponses

Purpose: Characterize recovery kinetics of fish cone ohotoresoonses. Method: We recorded photocurrents of green sunfish and goldfish single cones in fish Ringer's at room temperature with suction electrodes in response to brief flashes covering 3-4 log units of intensity. Results: In response to saturating (or nearly saturating) flashes fish cone photocurrents exhibit two distinct recovery components: an initial, rapid component (1) which accounts for most of the recovery to justsaturating flashes, and a second, slower component (2). Component (1) is nearly isomorphic over flash intensity, and translates on the time axis for near-saturating intensities with distinct increment te per e-fold change in flash intensity. For different cones T, ranges from 40 to 200 ms (avg. TC = 95 ms for 10 cones). Component (2) progressively increases in relative magnitude and apparent time constant at higher intensities. Conclusion: By analogy to recent analyses of rod photocurrent recovery, TC (component 1) may represent the lifetime of the cone G, while component (2) may be caused by a slowly inactivatinq but low specific activity form of cone R.