Cloning and Functional Expression of Two Families of β-Subunits of the Large Conductance Calcium-activated K+ Channel

Abstract

We report here a characterization of two families of calcium-activated K ؉ channel ␤-subunits, ␤2 and ␤3, which are encoded by distinct genes that map to 3q26.2-27. A single ␤2 family member and four alternatively spliced variants of ␤3 were investigated. These subunits have predicted molecular masses of 27.1-31.6 kDa, share ϳ30 -44% amino acid identity with ␤1, and exhibit distinct but overlapping expression patterns. Coexpression of the ␤2 or ␤3a-c subunits with a BK ␣-subunit altered the functional properties of the current expressed by the ␣-subunit alone. The ␤2 subunit rapidly and completely inactivated the current and shifted the voltage dependence for activation to more polarized membrane potentials. In contrast, coexpression of the ␤3a-c subunits resulted in only partial inactivation of the current, and the ␤3b subunit conferred an apparent inward rectification. Furthermore, unlike the ␤1 and ␤2 subunits, none of the ␤3 subunits increased channel sensitivity to calcium or voltage. The tissue-specific expression of these ␤-subunits may allow for the assembly of a large number of distinct BK channels in vivo, contributing to the functional diversity of native BK currents.

Mechanism of the modulation of BK potassium channel complexes with different auxiliary subunit compositions by the omega-3 fatty acid DHA

“…We showed previously that DHA increased currents through native BK channels in vascular smooth muscle cells as well as heterologously expressed Slo1+β1 channels (27). Here we examined whether DHA stimulates Slo1 channels with other subunit compositions: Slo1 alone, Slo1+β2 (18,19), Slo1+β4 (6), and Slo1+LRRC26 (γ1) (3,4). Because coassembly with wild-type β2 introduces inactivation mediated by the β2 N terminus in the resulting channel complex (35), we also examined the impact of β2 with a deletion in the N terminus (Δ2-19) to remove inactivation (18,19).…”

“…Here we examined whether DHA stimulates Slo1 channels with other subunit compositions: Slo1 alone, Slo1+β2 (18,19), Slo1+β4 (6), and Slo1+LRRC26 (γ1) (3,4). Because coassembly with wild-type β2 introduces inactivation mediated by the β2 N terminus in the resulting channel complex (35), we also examined the impact of β2 with a deletion in the N terminus (Δ2-19) to remove inactivation (18,19). Pore-forming Slo1 and auxiliary subunits were coexpressed in human embryonic kidney (HEK) cells and studied using the inside-out patch-clamp method.…”

“…Inclusion of the auxiliary subunits in Slo1 BK channel complexes markedly alters their cellular targeting, pharmacological properties, and gating characteristics (2,3,6,9,18,19). For example, activation and deactivation kinetics of Slo1+β1 and Slo1+ β4 channels are markedly slower than those of Slo1 alone without any auxiliary subunit (hereafter referred to as Slo1 channels) (5) and the apparent Ca 2+ sensitivity of Slo1+β1 channels is also greater (20,21).…”

Closed state-coupled C-type inactivation in BK channels

“…BK channels are noninactivating K + channels, except in the presence of a β2 or β3 auxiliary subunit whose N-terminal peptide sequence occludes the channel pore in a more N-type inactivation manner (31)(32)(33). We found that, even under nearly K + -free conditions in the external recording solution, WT BK channels did not show any significant inactivation up to 10 s. The presence of Tyr at the BK channel 294 position (equivalent to the 449 position in Shaker channels) might partly contribute to the noninactivation because the T449Y mutation slows down C-type inactivation in Shaker channels (25).…”

Coassembly of Big Conductance Ca2+-activated K+ Channels and L-type Voltage-gated Ca2+ Channels in Rat Brain

“…Functional BK channels (also called maxi-K or slo channels) are tetrameric structures consisting of four pore forming ␣ subunits (the principal subunits). In addition, four different ␤ subunits (auxiliary subunits) have been identified (15)(16)(17)(18)(19).…”