Fig. 4.

Whole-cell sodium current amplitude is reduced in Rohon–Beard cells of touch-insensitive mutants. A, Voltage-activated sodium currents were recorded from neurons in unaffected sibling embryos (48 hpf; left) and homozygousmao mutant (48 hpf; top right), homozygous ali mutant (48 hpf; middle right), and homozygous ste mutant (48 hpf;bottom right) embryos. The slower inactivation observed in the recordings from Rohon–Beard cells of stehomozygous mutant and unaffected siblings is a typical finding forste mutants and the majority of sibling controls, of which $\frac{2}{3}$ are expected to be heterozygous. For themao mutant and unaffected sibling exemplars that are shown (top), NaCl had not been added to the pipette solution (see Materials and Methods). B, Mutations inali and ste lead to a variable and an overall smaller reduction of sodium current amplitude than does the mutation of mao. The plot shows the distributions of peak sodium current amplitude recorded from neurons ofmao, ali, and stehomozygous mutants and their unaffected siblings; theasterisks and circles designate the mean and individual values, respectively. Embryos ranged in age between 36 and 60 hpf.