Arachidonic acid inhibition of L-type calcium (CaV1.3b) channels varies with accessory CaVβ subunits

Abstract

Arachidonic acid (AA) inhibits the activity of several different voltage-gated Ca2+ channels by an unknown mechanism at an unknown site. The Ca2+ channel pore-forming subunit (CaVα1) is a candidate for the site of AA inhibition because T-type Ca2+ channels, which do not require accessory subunits for expression, are inhibited by AA. Here, we report the unanticipated role of accessory CaVβ subunits on the inhibition of CaV1.3b L-type (L-) current by AA. Whole cell Ba2+ currents were measured from recombinant channels expressed in human embryonic kidney 293 cells at a test potential of −10 mV from a holding potential of −90 mV. A one-minute exposure to 10 µM AA inhibited currents with β1b, β3, or β4 58, 51, or 44%, respectively, but with β2a only 31%. At a more depolarized holding potential of −60 mV, currents were inhibited to a lesser degree. These data are best explained by a simple model where AA stabilizes CaV1.3b in a deep closed-channel conformation, resulting in current inhibition. Consistent with this hypothesis, inhibition by AA occurred in the absence of test pulses, indicating that channels do not need to open to become inhibited. AA had no effect on the voltage dependence of holding potential–dependent inactivation or on recovery from inactivation regardless of CaVβ subunit. Unexpectedly, kinetic analysis revealed evidence for two populations of L-channels that exhibit willing and reluctant gating previously described for CaV2 channels. AA preferentially inhibited reluctant gating channels, revealing the accelerated kinetics of willing channels. Additionally, we discovered that the palmitoyl groups of β2a interfere with inhibition by AA. Our novel findings that the CaVβ subunit alters kinetic changes and magnitude of inhibition by AA suggest that CaVβ expression may regulate how AA modulates Ca2+-dependent processes that rely on L-channels, such as gene expression, enzyme activation, secretion, and membrane excitability.

L-type calcium channel β subunit modulates angiotensin II responses in cardiomyocytes

“…30 In line with these results, we show that DAGL activity is necessary for AngII-mediated L-type calcium channel inhibition, suggesting that AA production is necessary for this effect and indicating that ancillary calcium channel subunits can serve to fine-tune second messenger modulation of several VDCCs.…”

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

“…An alternate possibility is that ␤ 2X13 may affect modulation of Ca v 1.4 by other factors. For example, Ca v 1.3 channels containing ␤ 2a but not other ␤ subunits are relatively resistant to inhibition by arachidonic acid (61). Because synaptic Ca 2ϩ currents in salamander photoreceptors are strongly inhibited by arachidonic acid (62), it will be of interest to determine whether ␤ 2X13 alters the sensitivity of Ca v 1.4 channels to this arachidonic acid or other neuromodulators.…”

The β Subunit of Voltage-Gated Ca2+Channels

“…One example is the voltage-independent inhibition of HVA Ca 2+ channels upon PIP 2 depletion from the plasma membrane (171, 475). Another example is channel inhibition by arachidonic acid (AA), an unsaturated fatty acid released from phospholipids (including PIP 2 ) by the action of some phospholipases (18, 289, 374, 403). The magnitude of AA inhibition depends on the partnered Ca v β in the channel (374).…”

“…Another example is channel inhibition by arachidonic acid (AA), an unsaturated fatty acid released from phospholipids (including PIP 2 ) by the action of some phospholipases (18, 289, 374, 403). The magnitude of AA inhibition depends on the partnered Ca v β in the channel (374). In particular, β 2a seems to dampen AA inhibition of Ca v 1.3 channels.…”