Figure 6.

Dopamine hyperpolarizes membrane potential and reduces the input resistance of layer II fan cells. (a) Membrane potential was shifted to more hyperpolarized potentials by dopamine (*, P < .001). (b) Dopamine also reduced both peak and steady-state input resistance (*, P < .01). (c) Voltage responses to applied current steps before (c1) and after (c2) bath application of 50 μM dopamine in a representative cell. Action potentials are truncated. Circles in (c1) indicate the latencies at which peak and steady-state input resistance were measured. Inset traces in (c2) compare the initial voltage deflection to a −200 pA current step before and after application of dopamine. Arrows indicate voltage responses before and after dopamine that were similar in amplitude and which allow comparison of the magnitude of the inward rectification. Note also the reduced input resistance across the entire range of hyperpolarizing current pulses. (d) Current-voltage plots show peak and steady-state responses to current steps of increasing size. Arrows indicate points at which a comparable degree of inward rectification was observed during hyperpolarization to similar voltages before and after dopamine application.