Mechanism of Ca_v1.2 channel modulation by the amino terminus of cardiac β₂-subunits

L-type calcium channels are composed of a pore, α_1c (Ca_V1.2), and accessory β- and α₂δ- subunits. The β-subunit core structure was recently resolved at high resolution, providing important information on many functional aspects of channel modulation. In this study we reveal differential novel effects of five β₂-subunits isoforms expressed in human heart (β_2a-e) on the single L-type calcium channel current. These splice variants differ only by amino-terminal length and amino acid composition. Single-channel modulation by β₂-subunit isoforms was investigated in HEK293 cells expressing the recombinant L-type ion conducting pore. All β₂-subunits increased open probability, availability, and peak current with a highly consistent rank order (β _2a≈β_2b>β_2e≈β _2c>β_2d). We show graded modulation of some transition rates within and between deep-closed and inactivated states. The extent of modulation correlates strongly with the length of amino-terminal domains. Two mutant β₂-subunits that imitate the natural span related to length confirm this conclusion. The data show that the length of amino termini is a relevant physiological mechanism for channel closure and inactivation, and that natural alternative splicing exploits this principle for modulation of the gating properties of calcium channels.