Increase of Ca_V3 channel activity induced by HVA β1b-subunit is not mediated by a physical interaction

Low voltage-activated (LVA) calcium channels are crucial for regulating oscillatory behavior in several types of neurons and other excitable cells. LVA channels dysfunction has been implicated in epilepsy, neuropathic pain, cancer, among other diseases. Unlike for High Voltage-Activated (HVA) channels, voltage-dependence and kinetics of currents carried by recombinant LVA, i.e., Ca_V3 channels, are quite similar to those observed in native currents. Therefore, whether these channels are regulated by HVA auxiliary subunits, remain controversial. Here, we used the α1-subunits of Ca_V3.1, Ca_V3.2, and Ca_V3.3 channels, together with HVA auxiliary β-subunits to perform electrophysiological, confocal microscopy and immunoprecipitation experiments, in order to further explore this possibility.

Functional expression of Ca_V3 channels is up-regulated by all four β-subunits, although most consistent effects were observed with the β1b-subunit. The biophysical properties of Ca_V3 channels were not modified by any β-subunit. Furthermore, although β1b-subunits increased colocalization of GFP-tagged Ca_V3 channels and the plasma membrane of HEK-293 cells, western blots analysis revealed the absence of physical interaction between Ca_V3.3 and β1b-subunits as no co-immunoprecipitation was observed. These results provide solid evidence that the up-regulation of LVA channels in the presence of HVA-β1b subunit is not mediated by a high affinity interaction between both proteins.