Figure 3.

Serotonin activates GIRK-like channels. A, Voltage-clamp, oscillating TIDA neuron recorded in the presence of TTX. Application of 5-HT results in an outward current. Right, Gaussian fits of averaged (solid lines) holding current frequency distributions in control (green), 5-HT (red), and wash (black) (n = 10), sharing its y-axis with the raw trace. Dashed lines indicate raw data used to produce averages. Calibration: 5 s. Ai, Averaged 5-HT induced current ± SEM obtained by the digital subtraction of voltage-clamp ramps in control and at peak of 5-HT response (n = 10). Aii, Linear extrapolation of the 5-HT-induced current indicated by the box in Ai. There is projected reversal potential (E_rev) of −128.1 mV. B, Voltage-clamp, oscillating TIDA neuron recorded as in Figure 3A, and with Cs⁺-based intracellular solution used to block K⁺-currents. Application of 5-HT induces a substantially reduced outward current (compare A). Right, Gaussian fits of holding current frequency distributions in control (green) and 5-HT (red). (n = 10). Calibration: 10 s. Bi, Averaged current-voltage relationship ± SEM of I_5-HT in control (green, n = 10) and with Cs⁺-based intracellular solution (red, n = 10), obtained as in Ai. There is reduction of I_5-HT when Cs⁺-based intracellular solution is used. Bii, Box plot of I_5-HT recorded in voltage clamp with Cs⁺-based or control intracellular solution. Boxes represent 25th, 50th, and 75th percentile with superimposed mean ± SEM and maximum and minimum values (control n = 10, Cs⁺ n = 10). C, Voltage-clamp, oscillating TIDA neuron recorded as in A in the presence of high extracellular K⁺. Application of 5-HT fails to induce a significant current (n = 10). Calibration 5 s. Ci, Averaged current-voltage relationship ± SEM of I_5-HT in the presence of High extracellular K⁺ (n = 10), obtained as shown in Ai. There is a shift of the reversal potential and presence of inward rectification (compared Ai). Cii, High [K⁺]^O significantly reduces I_5-HT. Box plot organized as Bii (control n = 10, High [K⁺]^O n = 10). D, Voltage-clamp trace, oscillating TIDA neuron recorded as in A (there is abolishment of oscillation in response to TTX). 5-HT is applied before, during, and after Ba⁺ is present in the bath. There is Ba⁺-induced reduction of I_5-HT. Calibration: 10 pA, 60 s. Di, Ba⁺ significantly and reversibly reduces I_5-HT. Box plot organized as Bii (n = 5). Dii, TQ (n = 5) and the G-protein inhibitor NEM (control n = 10, NEM n = 5) significantly reduces I_5-HT. Box plot organized as Bii. ***p < 0.005. ns, Not significant.