Auxiliary subunit regulation of high‐voltage activated calcium channels expressed in mammalian cells

Abstract

The effects of auxiliary calcium channel subunits on the expression and functional properties of high-voltage activated (HVA) calcium channels have been studied extensively in the Xenopus oocyte expression system, but are less completely characterized in a mammalian cellular environment. Here, we provide the first systematic analysis of the effects of calcium channel b and a2-d subunits on expression levels and biophysical properties of three different types (Cav1.2, Cav2.1 and Cav2.3) of HVA calcium channels expressed in tsA-201 cells. Our data show that Cav1.2 and Cav2.3 channels yield significant barium current in the absence of any auxiliary subunits. Although calcium channel b subunits were in principle capable of increasing whole cell conductance, this effect was dependent on the type of calcium channel a1 subunit, and b3 subunits altogether failed to enhance current amplitude irrespective of channel subtype. Moreover, the a2-d subunit alone is capable of increasing current amplitude of each channel type examined, and at least for members of the Cav2 channel family, appears to act synergistically with b subunits. In general agreement with previous studies, channel activation and inactivation gating was regulated both by b and by a2-d subunits. However, whereas pronounced regulation of inactivation characteristics was seen with the majority of the auxiliary subunits, effects on voltage dependence of activation were only small (< 5 mV). Overall, through a systematic approach, we have elucidated a previously underestimated role of the a2-d1 subunit with regard to current enhancement and kinetics. Moreover, the effects of each auxiliary subunit on whole cell conductance and channel gating appear to be specifically tailored to subsets of calcium channel subtypes.

Expression of Rem2, an RGK Family Small GTPase, Reduces N-Type Calcium Current without Affecting Channel Surface Density

“…First, Rem2 expression abolished (below detectable levels) I Ca in a subset of both SCG neurons and in cells stably expressing N-type Ca 2ϩ channels. This result is contrary to data obtained from HVA Ca 2ϩ channels expressed without overt Ca V ␤ in which detectable current flowing through the modified channels was recorded (Meir et al, 2000;Yasuda et al, 2004). Second, the loss of Ca V ␤ would be expected to shift the activation of the channel to more depolarized potentials (Dolphin, 2003).…”

Characterization of Cav1.4 Complexes (α11.4, β2, and α2δ4) in HEK293T Cells and in the Retina

“…9D). The effect of ␤ 2a in slowing VDI of Ca v 1.2 is less profound than observed for other Ca v channels (59), so it may be that Ca v 1.2 VDI is somehow more resistant to modulation by ␤ 2a subunits than Ca v 1.4, such that the distinct effects of ␤ 2a and ␤ 2X13 on VDI are more readily resolved in Ca v 1.4 than Ca v 1.2.…”

Differential Role of N-Type Calcium Channel Splice Isoforms in Pain

“…This likely results from the association of Ca V 2.2 subunits with different ancillary subunits and from celldependent alternate splicing of Ca V 2.2 RNA (Lipscombe et al, 2002;Yasuda et al, 2004). Here we show that different splice isoforms of Ca V 2.2 mediate distinct physiological functions.…”