β subunit heterogeneity in N-type Ca²⁺ channels

The β subunit of the voltage-dependent Ca²⁺ channel is a cytoplasmic protein that interacts directly with an α₁ subunit, thereby modulating the biophysical properties of the channel. Herein, we demonstrate that the α_1B subunit of the N-type Ca²⁺ channel associates with several different β subunits. Polyclonal antibodies specific for three different β subunits immunoprecipitated ¹²⁵I-ω-conotoxin GVIA binding from solubilized rabbit brain membranes. Enrichment of the N-type Ca²⁺ channels with an α_1B subunit-specific monoclonal antibody showed the association of β_1b, β₃, and β₄ subunits. Protein sequencing of tryptic peptides of the 57-kDa component of the purified N-type Ca²⁺ channel confirmed the presence of the β₃ and β₄ subunits. Each of the β subunits bound to the α_1B subunit interaction domain with similar high affinity. Thus, our data demonstrate important heterogeneity in the β subunit composition of the N-type Ca²⁺ channels, which may be responsible for some of the diverse kinetic properties recorded from neurons.