Abstract
Voltage-gated calcium channels, which play key roles in many physiological processes, are composed of a pore-forming alpha 1 subunit associated with up to three auxiliary subunits. In vertebrates, the role of auxiliary subunits has mostly been studied in heterologous systems, mainly because of the severe phenotypes of knock-out animals. The genetic model Caenorhabditis elegans has all main types of voltage-gated calcium channels and strong loss-of-function mutations in all pore-forming and auxiliary subunits; it is therefore a useful model to investigate the roles of auxiliary subunits in their native context. By recording calcium currents from channel and auxiliary subunit mutants, we molecularly dissected the voltage-dependent calcium currents in striated muscle of C. elegans. We show that EGL-19 is the only alpha 1 subunit that carries calcium currents in muscle cells. We then demonstrate that the alpha 2/delta subunit UNC-36 modulates the voltage dependence, the activation kinetics, and the conductance of calcium currents, whereas another alpha 2/delta subunit TAG-180 has no effect. Finally, we characterize mutants of the two beta subunits, CCB-1 and CCB-2. CCB-1 is necessary for viability, and voltage-dependent calcium currents are abolished in the absence of CCB-1 whereas CCB-2 does not affect currents. Altogether these results show that EGL-19, UNC-36, and CCB-1 underlie voltage-dependent calcium currents in C. elegans striated muscle.