Figure 2. Somatic hyperpolarization-gated, sustained Cl⁻-conductance mediated by ClC–2.

(a) Whole-cell recordings from the somata and proximal apical dendrites of pyramidal cells with different [Cl⁻]_pip (4mM: n_soma=14, n_dendrite=4; 120mM: n_soma=11, n_dendrite=4; shading indicates the difference current reflecting whole-cell Cl⁻ current). (b) Time-dependent decrease of PV-IPSCs after stepping the membrane voltage of the postsynaptic cell from +60 mV to −90 mV in rat. (c) Large sustained somatic Cl⁻-conductance in somata of CA1 pyramidal cells in the wild-type (ClC–2^+/+) but not the ClC–2^−/− mice (4mM: n_soma,+/+ =13, n_soma,−/− =20; 120mM: n_soma,+/+ =24, n_soma,−/− =24). (d) Current-voltage plots of PV-IPSCs from ClC–2^+/+ (n=6 pairs) and ClC–2^−/− (n=3 pairs). Inset: PV-IPSCs from ClC–2^−/− mice compared to ClC–2^+/+ (example traces at −70 mV; [Cl⁻]_pip=40 mM). (e) Significantly decreased outward rectification of the PV-IPSCs in the ClC–2^−/− mice, and lack of change in rectification in the case of CCK-IPSCs. (f) Slower time-dependent decrease of PV-IPSCs after stepping the membrane voltage of the postsynaptic cell from +60 mV to −90 mV in the ClC–2^−/− mice compared to ClC–2^+/+. Asterisks indicate significant difference (note that the larger IPSCs indicated by asterisks in these Cl⁻ extrusion experiments are in general agreement with the presence of larger IPSCs at hyperpolarized holding potentials in the ClC–2^−/− animals in Fig. 2d).