Figure 8. Extracellular Ba²⁺ does not block I_h.

A, currents elicited by hyperpolarizing voltage steps (1 s duration, from −30 to −130 mV with 10 mV decrements) before and during the bath application of BaCl₂ (1 mM). B, plots of I_in (▪) and I_ss (□) in the control medium, and I_in (•) and I_ss (○) during the application of BaCl₂. Note that extracellular Ba²⁺ caused a marked inward shift of the holding current and a slight decrease in the leak conductance, but no significant change in the amplitude of I_h. C, recordings of the membrane potential and input resistances before, during and after the bath application of BaCl₂ (1 mM). The thick line indicates the period of the application of BaCl₂. A hyperpolarizing current pulse (160 pA, 100 ms duration) was injected every 10 s to monitor the input resistance changes. Note a marked membrane depolarization with an increase in the input resistance during the effect of extracellular Ba²⁺. D, enlargements of the voltage responses to the hyperpolarizing current pulses before (a), during (b) and after (c) the bath application of BaCl₂.