Fig. 6. 5-HT inhibits K⁺ channels of the interneurons in layer III to enhance GABA release.

A, Replacement of extracellular Na⁺ with the same concentration of NMDG failed to change 5-HT-indueced increases in inward holding currents (n=9). B, Omission of extracellular Ca²⁺ did not alter 5-HT-induced increases in inward holding currents (n=8). C, Voltage-current relationship recorded by a ramp protocol (from −130 mV to −60 mV, at a speed of 0.1 mV/ms) before and during the application of 5-HT (100 µM) when the extracellular K⁺ concentration was 3.5 mM. Traces in the figure were averaged traces from 5 cells. The 5-HT-induced net current reversed at ~−83 mV close to the calculated K⁺ reversal potential (~−85.4 mV). D, 5-HT-induced increases in holding currents were insensitive to TEA (n=9), Cs⁺ (n=8), 4-AP (n=9) and tertiapin (n=8). E, Bath application of Ba²⁺ (3 mM) induced an inward holding current and significantly reduced 5-HT-induced increases in holding currents (n=6). F, Bath application of bupivacaine (400 µM) induced an inward holding current and significantly attenuated 5-HT-induced augmentation of inward holding currents (n=5).