Structural determinants of CaV1.3 L-type calcium channel gating

channels, in particular the voltage dependence of activation (V 0.5 ) and Ca 2+ dependent inactivation (CDI). A functional CTM is present in the long C-terminus of human and mouse Ca v 1.3 (Ca v 1.3 L ), but not in a rat long cDNA clone isolated from superior cervical ganglia neurons (rCa v 1.3 scg ). We therefore addressed the question if this represents a species-difference and compared the biophysical properties of rCa v 1.3 scg with a rat cDNA isolated from rat pancreas (rCa v 1.3 L ). When expressed in tsA-201 cells under identical experimental conditions rCa v 1.3 L exhibited Ca 2+ current properties indistinguishable from human and mouse Ca v 1.3 L , compatible with the presence of a functional CTM. In contrast, rCa v 1.3 scg showed gating properties similar to human short splice variants lacking a CTM. rCa v 1.3 scg differs from rCa v 1.3 L at three single amino acid (aa) positions, one alternative spliced exon (exon31), and a N-terminal polymethionine stretch with two additional lysines. Two aa (S244, A2075) in rCa v 1.3 scg explained most of the functional differences to rCa v 1.3 L . Their mutation to the corresponding residues in rCa v 1.3 L (G244, V2075) revealed that both contributed to the more negative V 0.5 , but caused opposite effects on CDI. A2075 (located within a region forming the CTM) additionally permitted higher channel open probability. The cooperative action in the double-mutant restored gating properties similar to rCa v 1.3 L . We found no evidence for transcripts containing one of the single rCa v 1.3 scg mutations in rat superior cervical ganglion preparations. However, the rCa v 1.3 scg variant provided interesting insight into the structural machinery involved in Ca v 1.3 gating.