Figure 6. Low extracellular Na⁺ concentration leads to I_Ca suppression in HEK 293 cells expressing recombinant Ca²⁺ channel.

A) Current-voltage relationship of I_Ca in 145mM (◇) and 10mM (▽) [Na]_o in HEK 293 cells expressing α_1c,77, β1, α₂δ subunits of the L-type Ca²⁺ channel (N=6). B–C) Representative traces from the same cell after reduction of [Na]_o to 120 mM (B) and 10 mM [Na]_o (C) with equi-osmolar substitution of remaining NaCl with sucrose. D) Representative time course of suppression in 120 mM external Na⁺. E) quantitative representation of I_Ba suppression in two concentrations of 120 mM and 10 mM [Na⁺]_o comparing substitution with both Cs⁺ and sucrose (N=5–6, p<0.004 for all three conditions). F) Activation and availability curves of the L-type Ca²⁺ channel in presence of 145 (◇) and 10 mM [Na]_o (△) using Cs⁺ as the substituting cation.