Figure 4.
Mutational analyses illustrating the intraconvertibility of exon 12a and exon 12b within molluscan LCav3 channels in generating highly sodium-permeant Cav3 T-type channels with a lysine residue in homologous position within the DII L5 extracellular loop. The relative degree of Na+ versus Ca2+ ion permeation was estimated in the fold change in peak current size (elicited from a voltage step to −40 mV from a holding potential of −110 mV) in the presence of external Na+ ions (Ca2+ and Na+ containing external solution) versus when large and weakly permeant monovalent ion, NMDG+, replaces external Na+ ions (Ca2+ and NMDG+ containing external solution). A, representative ionic current traces of WT and mutagenized LCaV3 channels and their current–voltage relations of their relative current size ensembles ±SEM. Black-colored current traces were recorded in the presence of external Ca2+ and weakly permeant cation (NMDG+), and the blue-colored (exon 12a containing) and magenta-colored (exon 12b containing) traces were recorded after replacement of NMDG+ with equimolar Na+. B, bar graphs ± SEM with scatterplot of replicates of recorded cells. Statistical significance was evaluated in a parametric one-way ANOVA with Tukey test, F(3,64) = 152.7, p < .0000001. Statistically significant differences (P < 0.05) are illustrated by (∗).