Novel CaV2.1 clone replicates many properties of Purkinje cell CaV2.1 current

Abstract

The P-type calcium current is mediated by a voltage-sensing Ca V2.1 α subunit in combination with modulatory auxiliary subunits. In Purkinje neurones, this current has distinctively slow inactivation kinetics that may depend on alternative splicing of the α subunit and/or association with different CaVβ subunits. To better understand the molecular components of P-type calcium current, we cloned a Ca V2.1 cDNA from total mouse brain. The full-length CaV2.1 isoform that we isolated (GenBank) contains sequences recently shown to be present in Purkinje neurones. In agreement with previously published work, the alternatively spliced amino acid V421, implicated in slow inactivation, was not encoded in and was absent from reverse transcription-polymerase chain reaction products generated from single Purkinje cells. Next, we studied the expression of the four known mouse auxiliary Ca Vβ2 isoforms in Purkinje neurones. Confirmation of the presence of CaVβ2a in Purkinje cells, previously shown by others to slow CaV2.1 kinetics, led us to characterize its influence on current dynamics. We studied currents generated by the clone coexpressed in tsA201 cells with four different CaVβ subunits. In addition to the well-documented slowing of open-state inactivation kinetics, coexpression with the CaVβ2a subunit also protected CaV2.1 channels from closed-state inactivation and prevented the channel from inactivating during physiological trains of action potential-like stimuli. This strong resistance to inactivation parallels the property of Purkinje neurone P-type currents and is suggestive of a role for Ca Vβ2a in modulating the inactivation properties of P-type calcium currents in Purkinje neurones. © The Authors (2007).