Fig. 1.
Light modulated the voltage-gated Ca current on catfish cone HCs. a, Dissociated cone HC (left; arrow indicates axon-like process) and rod HC (right). b, Biphasic light response of some cone HCs. Left, Ca current I-V relation before (black), shortly after (green), intermediately after (blue), and long after bright flash (red). Middle, time course of Ca-current modulation by light. Peak current plotted. Vertical bars at top indicate flashes. Colored arrows correspond to measurements on left panel. In this and subsequent figures, input resistance of recorded cell (to monitor recording stability) is indicated at top by the membrane current elicited by repetitive, 200-msec, -3 mV voltage steps. Time 0 designates onset of first light stimulus, as in other panels. 40-μm-diameter (480 nm) light spot centered on soma, delivering 3×108 photons μm-2 s-1 for 1 sec (first) and 30 sec (second). Right, collected results (n=7) showing fractional change in Ca current by light. Magenta shows average. Flash (arrowhead) was (1 to 3) × 108 photons μm-2 s-1 for 1 sec. Ca-Ringer and K-methanesulfonate pipette solution. c, Monophasic light response (decrease in Ca current) of other cone HCs. Same solutions and flash intensity as in b. 5 cells on right. d, Light had no effect on the other voltage-gated currents. Membrane potential stepped from -50 mV to 0 mV for Na current (n=8), to +60 mV for delayed-rectifier K current (n=7), and to -100 mV for inward-rectifier K current (n=8). Same intensity as above but for 2 to 30 sec. 400-, 440-, 540-, 600- and 680-nm light were also tried, but gave no responses either. K-methanesulfonate pipette solution. e, Light had no effect on glutamate- and GABA-induced currents. Same light as in d. Glutamate current recorded in Mg2+-free catfish Ringer and K-methanesulfonate pipette solution, n=6; GABA current recorded in normal catfish Ringer and KCl pipette solution, n=8. Both pipette solutions had 20 μM Cd2+ to block Ca current. Vhold = -50 mV.