Fig. 6. Analysis of growth factor-induced inhibition of Na+ current in PC12 cells expressing mutant PDGF receptors or a dominant-negative Ras mutant. A, PC12 cells expressing either F5, F579/581, F5/579, or F5/581 mutant PDGF receptors were differentiated by chronic treatment with 100 ng/ml NGF. Peak Na+ current amplitudes (open diamonds) are plotted as a function of time, showing inhibition in response to 20 ng/ml PDGF (horizontal bars). Recording protocols are described in Figure 1; *Raw datatraces selected for insets.B, Cumulative data for experiments described inA are shown. Whole-cell currents recorded during growth factor application were normalized to whole-cell currents recorded before growth factor application. Error bars represent the mean ± SEM of normalized Na+ current amplitudes;†Statistically significant difference from PC12 cells expressing the wtPDGF receptor. The values of n for each experimental group are, from left to right, 10, 20, 20, 15, and 14.C, Cumulative data for experiments with 17-2 PC12 cells, which express the dominant-negative mutant N17 Ras, are shown. Error bars represent the mean ± SEM of normalized whole-cell Na+ currents after acute application of 100 ng/ml NGF (solid columns) or 50 ng/ml bFGF (shaded columns) reached its maximum effect in either 17-2 cells or PC12 cells expressing the wtPDGF receptor; †Statistically significant difference from PC12 cells expressing the wtPDGF receptor. The values of n for each experimental group are, from left to right, 10, 8, 10, and 10.