FIGURE 4.
Current-voltage relationships of CaV1.3 alternatively spliced variants. A, schematic representation of alternatively spliced CaV1.3 channel constructs. The channel backbone consists of CaV1.3 (GenBank accession number: D38101, white box), whereas the cytosolic tail consists of CaV1.3 long form (CaV1.342), or alternatively spliced variants IQΔ, Δ41, 43S, 43S-2, Δ44, and 48S (black). The stop codons for IQΔ, Δ41, 43S, and 43S-2 are indicated by black and white filled circles. Numbering follows the CaV1.3 amino acid sequence. B–E, representative IBa (gray) and ICa (black) traces during depolarization to 10 mV for alternatively spliced constructs Δ41, 43S-2, Δ44, and 48S. The IBa and ICa traces were scaled to enable comparison between the two profiles. Current scales were drawn for both IBa (gray) and ICa (black). The time scales for each IBa and ICa pair are the same. F–I, normalized I-V plots for IBa of alternatively spliced constructs Δ41, 43S-2, Δ44, and 48S. The curves were fitted with the equation described under “Experimental Procedures.” In parentheses are the number of cells recorded. J-M, same as F-I, but for ICa. N-Q, calcium-dependent inactivation of current through alternatively spliced variants Δ41, 43S-2, Δ44, and 48S. The fraction of peak current, Ipeak, remained at time intervals of 300 ms upon depolarization for IBa and ICa. f value indicates the strength of the CDI. The curves are visual fits of the values plotted to facilitate comparison. The number of cells recorded are given in parentheses.