Inhibition of Cav1.4 channels by protons depends on the identity of the α2δ subunit.

Abstract

In retinal photoreceptors, CaV1.4 channels coassemble with the β2 and α2δ-4 subunits and regulate the release of neurotransmitter. Like other CaV channels, CaV1.4 undergoes a prominent inhibition by extracellular protons with low pH decreasing the maximal current amplitude (Imax) and depolarizing the half maximal activation voltage (Vh). However, the mechanisms underlying this form of regulation remain controversial. Here, we analyzed the role of subunit identity on proton-mediated inhibition of CaV1.4 (coexpressed with β2x13) in transfected HEK 293T cells. In cells cotransfected with α2δ-4, changing the extracellular pH from 8.0 to 6.25 caused a significantly greater inhibition of Imax (ΔIMax) and shift in Vh (ΔVh) (ΔIMax = 89.8 ± 1.1 %, ΔVh = 22.7 ± 1.7 mV) than in cells cotransfected with α2δ-1 (ΔIMax = 64.6 ± 4.9 %, ΔVh = 9.0 ± 1.4 mV) or expressing CaV1.4 alone (ΔIMax = 48.3 ± 3.0 %, ΔVh = 9.4 ± 2.1 mV). Notably, this effect of α2δ-4 was selectively diminished for a C-terminal variant of CaV1.4 channels with hyperpolarized voltage-dependence of activation due to a disease-causing mutation (K1591X) but not alternative splicing (CaV1.4 Δ47). The increase in ΔIMax due to α2δ-4 was significantly lower in cells expressing K1591X (11.0 ± 9.9 %) as compared to CaV1.4 (46.2 ± 0.7 %) and CaV1.4 Δ47 (28.7 ± 2.4 %). We conclude that α2δ-4 potentiates proton-mediated inhibition of CaV1.4 in a manner that is modified by pathological variations in the C-terminal domain of CaV1.4.