Figure 4.
The relative Cs+ permeability of astrocyte passive conductance and cloned TWIK-1 and TREK-1 K+ channels. A, Astrocyte reversal potential VM (at 0 currents) shifted when bath solutions were switched from normal aCSF containing 3.5 mm K+ to the modified aCSF solutions containing, in sequence, 70 mm K+, Rb+, and Cs+. Astrocyte VM (at 0 current) at the steady-state level was recorded for 2 s for each ionic condition by continuous current-clamp recording. B, E, The voltage ramp-induced whole-cell current traces recorded from two CHO cells, one transfected with TWIK-1 (B) and another with TREK-1 (E) K+ channels. In each case, the current traces recorded in 135 mm Na+ (black traces), 135 mm K+ (dashed black traces), and 135 mm Cs+ (gray traces) bath solutions are shown. C, F, Representative traces of TWIK-1 and TREK-1 K+ channel whole-cell currents recorded with Cs+- and K+-based solutions as indicated. For the TWIK-1 K+ channels, the Cs+-conducted whole-cell currents showed a strong outward rectification and the overall whole-cell current at +50 mV is significantly larger than that of the K+-conducted whole-cell currents (56.6 ± 5.9 pA/pF vs 31.6 ± 2.5 pA/pF, n = 6). The Cs+-conducted TREK-1 channel currents remained outwardly rectifying and were smaller compared with K+-mediated conductance (at +50 mV, 49.5 ± 4.8 pA/pF vs 1118.4 ± 137.7 pA/pF, n = 5). Calibration: 100 ms and 1 nA. D, The relative permeability of astrocyte passive conductance (gray bars), TREK-1 (black bars), and TWIK-1 (open bars) K+ channels to different monovalent ions. The relative permeability (PX/PK) values in each test were calculated from Equation 2.