Differential Expression of Four 3.1 Splice Variants in the Repeat III-IV Loop

Molecular cloning revealed the three isoforms($Ca_v3.1,\;Ca_v3.2,\;and\;Ca_v3.3$) of the T-type calcium channel subfamily. Expression studies exhibited their distinctive electrophysiological and pharmacological properties, accounting for diverse properties of T-type calcium channel currents previously characterized from isolated cells. However, electrophysiological properties of ion channels have shown to be more diversified by their splice variants. We here searched splice variants of rat $Ca_v3.1$ T-type channel by reverse-transcription-polymerase chain reaction(RT-PCR) to further explore diversity of $Ca_v3.1$. Interestingly, analyses of cloned RT-PCR products displayed that there were at least four splicing variants of rat $Ca_v3.1$ in the loop connecting repeats III and IV. Southern blot analyses indicated that the predominantly detected variant in brain was $Ca_v3.1a$(492 bp), which were rarely detected in most of peripheral tissues. Other two variants($Ca_v3.1c$, 546 bp; $Ca_v3.1d$, 525 bp) were detected in most of the tissues examined. The smallest isoform($Ca_v3.1b$, 471 bp) was rarely detected all the tissues. Electrophysiological characterization of the splicing variants indicated that the splice variants differ in inactivation kinetics and the voltage dependence of activation and inactivation as well.