The β1B Subunit Regulates the Activity of LVA Calcium Channels: Evidences for a Physical Interaction

Voltage-gated Ca2+ (CaV) channels are classified as Low Voltage- (LVA; or CaV3 channels) and High Voltage- (HVA) Activated channels. Both are formed by a main α1 subunit, which forms the conduction pore and senses the changes in membrane potential. It consists of four domains (I-IV), which are similar to one another and contain six transmembrane segments (S1-S6). Auxiliary subunits (β, α2δ y γ) have been described only for HVA channels; they regulate the main subunit expression level, voltage dependence and current kinetics. The loop between domain I and II of HVA α1 subunits contains a conserved sequence known as AID, where α1 and β subunits interaction take place. Despite such domain is not present in LVA α1 subunits, it has been shown that cells expressing heterologously LVA channels significantly increase its current density in the presence of β subunits. Recently it has been suggested a weak interaction between peptides of the I-II loop of CaV3.3 channels and the core of β1 subunit. Nevertheless this interaction has not been shown at the whole protein level. The main goal of this work was to investigate whether β subunits modulate LVA Ca2+ channels and to determine if these two proteins interact physically. By using the whole cell patch clamp technique, we found that β1b subunit increases the current density (63, 72 and 45 %) of HEK-293 cells expressing CaV3.1, CaV3.2 and CaV3.3, respectively. Then, with fusion fluorescent proteins and confocal microscopy, we detected changes in β1b cellular distribution in the presence of the CaV3.3 channel. Finally, by western blot we identified the protein complex formed by Cav3.3 and β1b. Altogether, these data suggested that HVA β subunits modulate LVA Ca2+ channels probably by a physical interaction.CONACYT-Mexico J50250Q.