Fig. 12.

Adaptation to the current variance persisted with Ca²⁺ and K⁺ currents suppressed. A, Suppression of Ca²⁺ and K⁺ currents. The voltage of an isolated ganglion cell was stepped from −60 to −20 mV for 200 msec. The current–responses in HEPES Ringer's solution (thick line) and in Ringer's solution with 200 μmBa²⁺, 400 μm Cd²⁺, and 500 nm apamin added (thin line) are shown. Suppression of Ca²⁺ and K⁺currents tripled the width at half-height of the average action potential and reduced the afterhyperpolarization (inset). B, Adaptation to changes in current variance without Ca²⁺ and K⁺ currents. Gaussian noise (bandwidth 0–50 Hz) was injected into the cell under current clamp. Linear filters are shown for injected currents with variances of 16 pA² (thick trace) and 144 pA² (thin traces). C, Adaptation to changes in current variance was similar with and without Ca²⁺ and K⁺ currents. Solid traces plot filters measured in HEPES Ringer's solution, and thedashed traces plot those measured with Ca²⁺ and K⁺ currents suppressed. The filters in the absence of blockers were calculated with identical stimuli with and without toxins. Holding current was −10 to −16 pA, chosen so the cell had similar mean firing rates in both conditions.