LAUSR

β‐Subunits of the Ca2+ channel have been conventionally regarded as auxiliary subunits that regulate the expression and activity of the pore‐forming α1 subunit. However, they comprise protein–protein interaction domains, such as a SRC homology 3 domain (SH3) domain, which make them potential signaling molecules. Here we evaluated the role of the β2a subunit of the Ca2+ channels (CaVβ2a) and its SH3 domain (β2a‐SH3) in late stages of channel trafficking in bovine adrenal chromaffin cells. Cultured bovine adrenal chromaffin cells were injected with CaVβ2a or β2a‐SH3 under different conditions, in order to acutely interfere with endogenous associations of these proteins. As assayed by whole‐cell patch clamp recordings, Ca2+ currents were reduced by CaVβ2a in the presence of exogenous α1‐interaction domain. β2a‐SH3, but not its dimerization‐deficient mutant, also reduced Ca2+ currents. Na+ currents were also diminished following β2a‐SH3 injection. Furthermore, β2a‐SH3 was still able to reduce Ca2+ currents when dynamin‐2 function was disrupted, but not when SNARE‐dependent exocytosis or actin polymerization was inhibited. Together with the additional finding that both CaVβ2a and β2a‐SH3 diminished the incorporation of new actin monomers to cortical actin filaments, β2a‐SH3 emerges as a signaling module that might down‐regulate forward trafficking of ion channels by modulating actin dynamics.