Figure 2. Effects of changing the [K⁺]_o on I_h.

A, currents elicited by hyperpolarizing voltage steps (1 s duration, from −60 to −130 mV with 10 mV decrements) in three different [K⁺]_o (1, 5 and 20 mM). The control ACSF contained 5 mM K⁺. All solutions contained TEA, Ba²⁺, 4-AP, TTX and nominally zero Ca²⁺. Note the outward and inward shifts of the holding current with 1 and 20 mM of [K⁺]_o, respectively. B, plots of the amplitude of I_h elicited at each value of [K⁺]_o. C, mean values for the effects of changing [K⁺]_o on I_h (n = 5). The conductance of I_h, estimated by calculation of the slope for each plot between −80 and −130 mV of the membrane potential, was compared with the control level. D, current elicited by voltage steps (1 s duration, from −50 to −130 mV with 10 mV decrements) in the low-Na⁺ solution containing TTX (1 μm) and three different concentrations of K⁺ (1, 5 and 20 mM). NaCl was substituted for choline chloride and K⁺ was simply added in the perfusate. E, plots of I_in (▪, •, ▴) and I_SS (□, ○, ▵) obtained from current traces in each [K⁺]_o as a function of the membrane potential. Note a marked increase in the amplitude of I_h at more negative membrane potentials (< −100 mV) and the dose-dependent inward shift of the holding current.