The carboxy-terminal tail region of human Cav2.1 (P/Q-type) channel is not an essential determinant for its subcellular localization in cultured neurones.

A recent report on the mechanism of synaptic targeting of Ca(v)2.2 channel suggested that this process depends upon the presence of long C-terminal tail and that protein interactions mediated by SH3-binding and PDZ-binding motifs in the tail region are important. To examine the possibility that C-terminal tail of the Ca(v)2.1 channel and the polyglutamine stretch therein are also involved in the mechanism for channel localization, we constructed several expression plasmids for human Ca(v)2.1 channel tagged with enhanced green fluorescent protein (EGFP) and introduced them into mouse hippocampal neuronal culture. HC construct encodes short version of Ca(v)2.1, and HS and HL encode Ca(v)2.1 channel with a long C-terminal tail, which contains polyglutamine tract of 13 (normal range) and 28 (SCA6 disease range) repeat units, respectively. Surprisingly, transfection with HC, HS, and HL gave essentially the same results: EGFP signal was observed in cell soma, dendrites, and the axon as well. Furthermore, mutation of the PDZ-binding motif located at the C-terminus of the long version of Ca(v)2.1, by adding FLAG tag, did not affect the localization patterns of HS and HL as well. Therefore, the C-terminal region is not indispensable for the subcellular localization of Ca(v)2.1 channel, nor expansion of polyglutamine length affected the localization of the channel. Thus, it is possible that the localization mechanism of Ca(v)2.1 channel is different from that of Ca(v)2.2, though these channels share various structural and functional characteristics.