Molecular cloning and characterization of a hamster Cav1.3 Ca<SUP>2+</SUP> channel variant with a long carboxyl terminus

초록

We have cloned a hamster Ca(v)1.3 variant with a long carboxyl terminus. This differs from the first hamster Ca(v)1.3 clone which has a short carboxyl terminus. When relative expression levels of the two variants were examined using quantitative RT-PCR, the long Ca(v)1.3 transcripts were detected abundantly in the brain and testis, moderately in the heart, pancreas, and kidney, and weakly in the lung. Comparatively, the short Ca(v)1.3 transcripts were detected less abundantly in most of the tissues. The two Ca(v)1.3 variants were reconstituted in Xenopus oocytes and their electrophysiological properties were characterized using a two-electrode voltage clamping method. The long Ca(v)1.3 variant was similar to 5-fold better expressed than the short Ca(v)1.3 variant. When Ca2+ was used as a charge carrier, the long Ca(v)1.3 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 Ca(v)1.3 were significantly lower than those of the short Ca(v)1.3. 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. (C) 2010 Elsevier B.V. All rights reserved.

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