Knockout of the LRRC26 subunit reveals a primary role of LRRC26-containing BK channels in secretory epithelial cells

Abstract

Leucine-rich-repeat-containing protein 26 (LRRC26) is the regulatory γ1 subunit of Ca 2+ -and voltage-dependent BK-type K + channels. BK channels that contain LRRC26 subunits are active near normal resting potentials even without Ca 2+ , suggesting they play unique physiological roles, likely limited to very specific cell types and cellular functions. By using Lrrc26 KO mice with a β-gal reporter, Lrrc26 promoter activity is found in secretory epithelial cells, especially acinar epithelial cells in lacrimal and salivary glands, and also goblet and Paneth cells in intestine and colon, although absent from neurons. We establish the presence of LRRC26 protein in eight secretory tissues or tissues with significant secretory epithelium and show that LRRC26 protein coassembles with the pore-forming BK α-subunit in at least three tissues: lacrimal gland, parotid gland, and colon. In lacrimal, parotid, and submandibular gland acinar cells, LRRC26 KO shifts BK gating to be like α-subunit-only BK channels. Finally, LRRC26 KO mimics the effect of SLO1/BK KO in reducing [K + ] in saliva. LRRC26-containing BK channels are competent to contribute to resting K + efflux at normal cell membrane potentials with resting cytosolic Ca 2+ concentrations and likely play a critical physiological role in supporting normal secretory function in all secretory epithelial cells.L arge-conductance, voltage-and Ca 2+ -regulated BK-type channels are widely expressed proteins, found not only in excitable cells, such as neurons, muscle, and endocrine cells, but also nonexcitable cells, including salivary (1) and lacrimal gland (2) acinar cells, and colonic crypt cells (3). Given the almost ubiquitous expression of BK channels among cells that play quite distinct physiological roles, it is particularly important to define the specific properties of BK channels in a given cell type and determine what the specific physiological role played by BK channels in a given cell may be. A hallmark of BK channels is their dual regulation by both membrane voltage and cytosolic Ca 2+ (4), both properties embedded within the tetramer of pore-forming α-subunits of each BK channel (5). However, the specific range of voltages over which a BK channel is active at a given Ca 2+ concentration is markedly dependent on the identity of regulatory subunits that can coassemble with the α-subunit in the mature channel complex. Of the two families of known BK regulatory subunits, β (6-11) and γ (12-14), an important feature of many of these subunits is the ability to shift the range of activation voltages at a given Ca 2+ . Although there is growing information about the loci of expression and functional roles of BK channels containing specific β-subunits (15), much less is known about those BK channels containing the γ1 (LRRC26, leucine-rich-repeat-containing subunit 26) subunit. However, LRRC26 is particularly fascinating because it causes the largest shift in BK gating (approximately −120 mV) of any known non-pore-forming regulatory subunit, resulting in BK channels that...

LRRC52 regulates BK channel function and localization in mouse cochlear inner hair cells

“…1B) (6,10). The initial member of this family, LRRC26, produces the largest leftward shift in BK gating of any known BK regulatory subunit, an ∼120to 130-mV shift in V h at any [Ca 2+ ] i (6,10,11) and appears largely confined to secretory epithelial cells (12). In secretory epithelial cells expressing endogenous LRRC26-containing BK channels or when LRRC26 is heterologously expressed together with BK α subunits, the V h of BK activation is about +35 mV at nominally 0 [Ca 2+ ] i ( Fig.…”

“…All mice were C57BL/6, with KO alleles backcrossed out to at least 8 generations. The Lrrc26 KO mice were as previously described (12) with the neomycin expression cassette present in the original Knockout Mouse Project (KOMP) Repository line deleted (12). The Lrrc52 KO mice were also described in previous work (16).…”

The large‐conductance voltage‐ and Ca2+‐activated K+ channel and its γ1‐subunit modulate mouse uterine artery function during pregnancy

“…Eight-to-twelve-week-old homozygous BK Ca −/− females and their WT littermates were mated to WT males, resulting in BK Ca +/− and WT offspring, respectively. Mice lacking the lrrc26 gene (γ1 −/− ) were kindly provided by Dr Christopher Lingle (Washington University in St Louis) (Yang et al 2017), and the colony was maintained as homozygous mutants. Day 0 of pregnancy was determined by the presence of a copulatory plug after mating for 2-3 h. Mice were killed by gradually increasing the CO 2 flow rate into the chamber and then performing cervical dislocation.…”

Glutamate-activated BK channel complexes formed with NMDA receptors

“…BK channels also control the contractile tone of smooth muscle and are involved in the regulation of vascular blood pressure (11), the urinary bladder (12), and erectile function (13). In nonexcitable secretory epithelial cells, BK channels provide an essential pathway for resting K + efflux (14).…”