Figure 5. Kir4.1 or Kir2.1•E224G channels maintain one stable level of resting membrane potential when co-expressed with HCN2 channels in CHO cells.

(A-B) Resting membrane potentials (top) and whole-cell ramp currents (bottom) of CHO cells that express (A) rat Kir4.1 or (B) human Kir2.1•E224G mutant channels before and after [K⁺]_e was changed from 5 mM to 2 mM. Kir4.1 reversal potentials shifted from −74.2 ± 1.0 mV to −97.4 ± 0.7 mV (n=5), whereas reversal potentials of Kir2.1•E224G channels shifted from −72.7 ± 1.0 mV to −95.8 ± 0.7 mV (n=6). (C-D) Resting membrane potentials (top) and whole-cell ramp currents (middle) of CHO cells that express (C) both Kir4.1 and HCN2 channels or (D) both Kir2.1•E224G and HCN2 channels before and after [K⁺]_e was decreased from 5 mM to 2 mM. Time scale, 100 s. Middle row: Black and pink lines indicate whole-cell ramp currents in 5 and 2 mM [K⁺]_e, respectively; purple and orange lines indicate the currents after sequential application of 0.5 mM Ba²⁺ and both 0.5 mM Ba²⁺ and 2 mM Cs⁺ in 2 mM [K⁺]_e, respectively; inserts, Magnifications of ramp currents between −150 pA to 100 pA, illustrating clearly small HCN currents. Bottom row: Resting membrane potentials (filled bars) of the cells and reversal potentials (open bars) of whole-cell currents recorded in 5 and 2 mM [K⁺]_e (n=4–17).