Figure 3. Effects of changing [Na⁺]_o on I_h.

A, currents elicited by hyperpolarizing voltage steps (inset) in control solution containing 150 mM Na⁺ (left panel), during reduction of [Na⁺]_o (50 mM, middle panel) and during washout with the control solution (right panel). Choline chloride was added as an equimolar substitute for NaCl. All recordings were made in the presence of TTX (1 μm). Note the decrease in the amplitude of I_ss and the slower time course of I_h activation during the low-Na⁺ solution. B, plots of I_in (▪, •) and I_ss (□, ○) obtained from current traces in A as a function of the membrane potential. Note a marked decrease in the amplitude of I_ss with no significant changes in the amplitude of I_in during recording with the low-Na⁺ solution.