Figure 6. Effects of I_Kx and I_h on the Voltage Response to Current Injection.

Current components were identified in the voltage-clamp mode, and voltage responses to square pulses of injected current were assessed in the same cell. In each condition, cells were made to “rest” at about –38 mV by injection of a constant holding current (Axopatch 1-C).

(A) To reveal I_h, recordings were made in the absence of Cs⁺ but in the presence of Cd²⁺. With both I_h (dominant at –95 mV) and I_Kx (dominant at –55 mV) present, a time-dependent decrease in both small and large voltage signals occurred.

(B) Recordings in both (B) and (C) were made from cells bathed in Ringer solution containing 5 mM Cs⁺ and 0.1 mM Cd²⁺. Bath application of 5 mM Cs⁺ blocked I_h, but left I_Kx. The small voltage signal was similar to the control but the large signal became sustained.

(C) Bath-applied 5 mM Ba²⁺ inhibited I_Kx in this voltage range (see Figure 5). No time- or voltage-dependent currents (other than capacity currents) were evident, and the response to the small hyperpolarizing current injection was much larger and did not decrease with time (the larger hyperpolarizing current step was not applied).