Figure 1.

Effect on the bright flash response in a salamander L-cone of superfusion with 0 Ca²⁺/0 Na⁺ solution. (A) Superimposed responses to bright flashes in Ringer's solution (heavy trace) and on exposure to 0 Ca²⁺/0 Na⁺ solution from 1 s before the flash until progressively increasing times thereafter (light traces). Top traces represent solution change and flash monitors. Suction pipette currents include a junction current resulting from the liquid junction potential between the dissimilar solutions in pipette and bath. Traces are the average of four responses in Ringer's solution and two responses in 0 Ca²⁺/0 Na⁺ solution; measurements were bracketed symmetrically in time. The bright flash delivered 1.22 × 10⁶ photons µm⁻² at 578 nm. In 0 Ca²⁺/0 Na⁺ solution, sodium ions have been replaced with choline; the virtual absence of external permeant ions abolished the inward dark current, but unlike the situation in rods, little outward potassium current was recorded, perhaps as a result of inner segment hyperpolarization (Matthews, 1995, 1996; Lyubarsky et al., 1996). (B) Recovery phases of the responses from A after subtraction of the junction current obtained upon the return to Ringer's solution after a 2-s exposure to 0 Ca²⁺/0 Na⁺ solution during saturating light at the end of the experiment. For each trace, the junction current has been offset in time to coincide with the return to Ringer's solution. Data have been digitally low-pass filtered at 20 Hz. Heavy trace denotes response in Ringer's solution. (C) Dependence of response duration on the time spent in 0 Ca²⁺/0 Na⁺ solution after the flash. Response duration was measured as the time taken after the flash for the response to recover 25% of the original dark current in Ringer's solution (interrupted line in B); times of solution changes measured from the half-relaxation time of the junction current. Regression line of slope 0.52 fitted using a least-squares algorithm.