Fig. 6.

Sodium dependence of inward rectification.A, Responses of an octopus cell to hyperpolarizing current steps of different magnitudes in normal physiological saline and saline in which extracellular sodium was reduced from 130 to 20 mm. The reduction of extracellular sodium hyperpolarized the cell and reduced the sag toward rest. B, Steady-state voltage–current relationship of the same cell shows an increase in the input resistance over the hyperpolarizing voltage range. C, The difference between the steady-state and peak voltages (indicated in A by arrows) in three different cells during the response to a −4.0 nA current step in normal and reduced extracellular sodium shows a statistically significant reduction in the mean sag in the presence of low extracellular sodium (Student’s t test;p < 0.05; n = 3).