FIG. 4.
Divalent ions modulate the light-activated current. (A) Upper: the average light response amplitude is significantly smaller when 18 mM BAPTA (black) is included in the pipette compared with 10 mM EGTA (hatched) and 0.1 mM (grey). Lower: the rate of the response is significantly longer in 18 mm BAPTA than in 0.1 mM EGTA. (B) Upper: light responses were normalized to the first maximal light response and the averages for each group plotted over 1600 s. Both cells with 0.1 mM EGTA (●) and cells with 10 mM EGTA (■) in the pipette solution reached a steady-state light response amplitude around 50% of initial amplitude. Lower: the time constants of rundown were calculated by fitting data from each cell to a single exponential decay and averaging within a group. (C) Upper: increasing internal magnesium from 1 mM to 4 mM reduced the amplitude of the light response. Lower: the increase in magnesium also slowed the development of the lightactivated inward current. Neither of these findings were significant by Student's t-test. Asterisks indicate: P < 0.004 compared with 10 mM EGTA in A upper panel; P < 0.025 in A lower panel; P = 0.05 in panel B.