Figure 4.
Resensitization of human 5-HT3A receptors. A, Representative series of nine pairs of current traces obtained from the same cell expressing 5-HT3A receptors using different desensitization recovery times. Cells were perfused with 100 μm 5-HT for 15 s. After a recovery time ranging from 1 to 30 s, a second test pulse of 100 μm 5-HT was applied for 1 s. B, Recovery time dependence of the peak response to the second 5-HT pulse normalized to the peak response of the first 5-HT pulse. Desensitization was induced by prolonged exposure of receptors to either 5-HT or DA. The inset shows the first 3 s on an expanded timescale. Each data point represents the mean ± SD. The solid curves are single-exponential fits of the 5-HT and DA datasets. The two curved lines are fits of the 5-HT and DA datasets to the Hodgkin–Huxley equation. For 5-HT, Imax, m, and τ were 0.936 ± 0.003, 3.8 ± 0.1, and 4.83 ± 0.07 s, respectively. For DA, these values were 0.87 ± 0.03, 0.79 ± 0.1, and 1.4 ± 0.3 s, respectively.