Molecular cloning and characterization of a hamster Cav1.3 Ca2+ channel variant with a long carboxyl terminus

We have cloned a hamster Cav1.3 variant with a long carboxyl terminus. This differs from the first hamster Cav1.3 clone which has a short carboxyl terminus. When relative expression levels of the two variants were examined using quantitative RT-PCR, the long Cav1.3 transcripts were detected abundantly in the brain and testis, moderately in the heart, pancreas, and kidney, and weakly in the lung. Comparatively, the short Cav1.3 transcripts were detected less abundantly in most of the tissues. The two Cav1.3 variants were reconstituted in Xenopus oocytes and their electrophysiological properties were characterized using a two-electrode voltage clamping method. The long Cav1.3 variant was ~5-fold better expressed than the short Cav1.3 variant. When Ca2+ was used as a charge carrier, the long Cav1.3 variant containing an IQ (Ile-Gln) motif displayed strong calcium-dependent inactivation, while the short variant that was deficient of an IQ motif showed little calcium-dependent inactivation. Examination of other biophysical properties revealed that potentials for activation threshold, peak current, and half-activation and inactivation of the long Cav1.3 were significantly lower than those of the short Cav1.3. These findings suggest that the long carboxyl tail plays crucial roles in not only facilitating calcium-dependent inactivation, but also improving expression and negative shifting of the activation and inactivation properties.