Figure 2. Control of Resting Na⁺ Leak Current by Extracellular Ca²⁺ in Cultured Hippocampal Neurons.

(A) Representative holding currents at –68 mV in a wild-type (+/+) neuron. Na⁺-leak current is presented as ΔI_L-Na (indicated by the double arrow), defined as the difference between holding currents in 140 mM (solid bar) and 14 mM (open bar) Na⁺-containing baths. A 0.25 sec recording is shown for each condition. ΔI_L-Na increased when [Ca²⁺]_e was switched from 2 mM (indicated by the hatched bar labeled 2 Ca) to 0.1 mM (0.1 Ca). (B) ΔI_L-Na in wild-type neurons measured at various [Ca²⁺]_e normalized to that measured with 2 mM [Ca²⁺]_e (n ≥ 5). (C) Similar to (A), but from a NALCN^-/- neuron. (D) Comparison of ΔI_L-Na between wild-type (+/+) and NALCN^-/- neurons at a range of [Ca²⁺]_e, as indicated. The number of cells for each condition is indicated in parentheses. (E) Representative ΔI_L-Na restored by NALCN cDNA transfection into the NALCN^-/- neurons. (F) Summary of ΔI_L-Na generated by NALCN or mock (empty vector) transfection in 2 mM and 0.1 mM [Ca²⁺]_e (mean ± SEM). See also Figure S2.