Influence of L-type Ca channel alpha 2/delta-subunit on ionic and gating current in transiently transfected HEK 293 cells

Abstract

We have measured ionic and gating currents in human embryonic kidney (HEK 293) cells transiently transfected with cDNAs encoding subunits of the cardiac voltage-gated L-type Ca2+ channel. Robust recombinant ionic current and associated nonlinear charge movement could be measured over a broad voltage range without contamination by endogenous channel activity. Coexpression of the alpha 2/delta-subunit along with alpha 1- and beta 2-subunits speeded activation and deactivation kinetics and significantly increased the maximal conductance of ionic current. Charge movement was measured at voltages negative to the threshold for activation of ionic current, and gating charge could be immobilized at positive holding potentials that did not inactivate ionic current. The ratio of maximal ionic conductance to maximal charge moved remained the same in the absence or presence of the alpha 2/delta-subunit. However, the maximal amount of charge moved was increased about twofold in the presence of the alpha 2/delta-subunit. These results suggest that coexpression of the alpha 2/delta-subunit enhances the expression of functional L-type channels and, in addition, provide evidence that most of the L-type channel-associated nonlinear charge movement is caused by transitions between nonconducting states of the channel protein that precede the open and inactivated states.

The calcium channel α2/δ1 subunit interacts with ATP5b in the plasma membrane of developing muscle cells

“…Colocalization was higher at the ends of the cell as seen from the merged image (Fig. 4Ac) and the binary mask, which agrees with the distribution of ␣2/␦1 in young myotubes we previously reported (2). For this particular cell, the Pearson's correlation coefficient (R r ) was 0.69 and the overlap coefficient (R) was 0.967.…”

Dissection of Functional Domains of the Voltage-Dependent Ca2+Channel α2δ Subunit

“…In support of this interpretation, Bangalore et al (1996) have demonstrated that the coexpression of the ␣ 2 ␦ complex increases the number of f unctional L -type calcium channels in the cell membrane as gauged by gating charge movement. In addition, Shistik et al (1995) have shown that the ␣ 2 ␦ complex triples the amount of ␣ 1C protein localized in the plasma membrane of Xenopus oocytes as detected by immunoprecipitation.…”

“…Expression of the cloned ␤ subunit results in an increase in current amplitude and changes the biophysical properties of the ␣ 1 pore-forming subunit (Mori et al, 1991; Hullin et al, 1992;Perez-Reyes et al, 1992;Neely et al, 1993Neely et al, , 1995Nishimura et al, 1993;Chien et al, 1995;Massa et al, 1995;Pérez-García et al, 1995;Kamp et al, 1996). Likewise, functional coexpression of the ␣ 2 ␦ subunit, the product of a single gene that is posttranslationally processed to yield separate subunits (␣ 2 and ␦) linked by disulfide bonds (De Jongh et al, 1990;Jay et al, 1991), also results in significantly increased macroscopic currents through ␣ 1 /␤ recombinant calcium channels (Singer et al, 1991;Itagaki et al, 1992;Williams et al, 1992;Shistik et al, 1995;Bangalore et al, 1996;Wiser et al, 1996). Effects on dihydropyridine (DHP) binding also have been attributed to expression of the ␤ and ␣ 2 ␦ auxiliary subunits (Welling et al, 1993;Mitterdorfer et al, 1994;Wei et al, 1995).…”

Differential behavioral state-dependence in the burst properties of CA3 and CA1 neurons

“…The LTCC consists of multiple subunits, and each subunit has multiple isoforms as a result of differential gene expression, alternative splicing, and post-translational modification (66). Different channel compositions give rise to different gating properties of the LTCC and may influence the different rates of deactivation tail current (67)(68)(69)(70)(71). The class Ca v 1.2 ␣ 1 subunit has been shown to contribute to forming an LTCC with anomalous gating properties characterized by rare and short openings with very low open probability during depolarization but long openings with high open probability after repolarization (70,72).…”