Cholesterol increases the open probability of cardiac KACh currents

Abstract

Cholesterol is one of the major lipid components of membranes in mammalian cells. In recent years, cholesterol has emerged as a major regulator of ion channel function. The most common effect of cholesterol on ion channels in general and on inwardly rectifying potassium (Kir) channels in particular is a decrease in activity. In contrast, we have recently shown that native G-protein gated Kir (GIRK or Kir3) channels that underlie atrial KACh currents are up-regulated by cholesterol. Here we unveil the biophysical basis of cholesterol-induced increase in KACh activity. Using planar lipid bilayers we show that cholesterol significantly enhances the channel open frequency of the Kir3.1/Kir3.4 channels, which underlie KACh currents. In contrast, our data indicate that cholesterol does not affect their unitary conductance. Furthermore, using fluorescent and TIRF microscopy as well as surface protein biotinylation, we also show that cholesterol enrichment in vitro has no effect on surface expression of GFP-tagged channels expressed in Xenopus oocytes or transfected into HEK293 cells. Together, these data demonstrate for the first time that cholesterol enhances Kir3-mediated current by increasing the channel open probability.

Dual activation of neuronal G protein-gated inwardly rectifying potassium (GIRK) channels by cholesterol and alcohol

“…Cholesterol inhibits constitutively open inwardly-rectifying potassium channels 25, 26 but appears to activate cardiac (GIRK1/GIRK4) and brain (GIRK2) channels 23, 27, 43 . Whether cholesterol acts directly on brain GIRK2 channels in the absence of Gβγ is unknown.…”

“…Similar to its effects on brain GIRK2 channels, cholesterol enhances acetylcholine activated potassium (K ACh ) channels in the heart, which are composed of GIRK1 and GIRK4 subunits 23, 27 . Interestingly, this effect was proposed to be independent of Gβγ but with little change in the apparent PIP 2 affinity 23 .…”

“…Another example of a putative G protein-independent modulator is cholesterol. Cholesterol, which accounts for up to 50% of the total lipid membrane content 22 , has been shown to modulate the activity of potassium channels 23–28 , including cardiac GIRK channels, i.e., GIRK1/GIRK4 subunits 23, 27 . However, whether cholesterol affects brain GIRK channels, comprised mostly of GIRK2-containing tetramers, requires Gβγ subunits, and interacts with alcohol-dependent activation is unknown 1 .…”

Cholesterol regulates polymodal sensory transduction in Müller glia

“…However, vanilloid TRPs may also be regulated through conserved cholesterol-binding CRAC (Cholesterol Recognition/Interaction Amino acid Consensus) domains that span the loop between TM4 and TM5 (amino acids 576 -632) of TRPV4 (Kumari et al, 2015) and CARC domains that mediate cholesterol binding in cognate TRPV1 (Picazo-Ju arez et al, 2011). CARC-containing TRPV1 and inwardly rectifying Kir3.1/Kir3.4 (GIRK) channels are inhibited by MbCD (Bukiya, Durdagi, Noskov, & Rosenhouse-Dantsker, 2017;Liu, Huang, Wu, & Priestley, 2006;Szoke et al, 2010) whereas cholesterol increases the open probability but not the unitary conductance of GIRK channels that subserve cardiac K ACh currents (Bukiya et al, 2015). The opposite effects were reported for Kir2.1-4 channels (Epshtein et al, 2009;Romanenko et al, 2004), BK channels (Bolotina, Omelyanenko, Heyes, Ryan, & Bregestovski, 1989), Kv1.5 channels (Abi-Char et al, 2007), N-type Ca 21 channels (Toselli et al, 2005), volume-sensitive Clchannels (Levitan, Christian, Tulenko, & Rothblat, 2000) and TRPM3/TRPM8 thermochannels (Morenilla-Palao, Pertusa, Meseguer, Cabedo, & Viana, 2009;Naylor et al, 2010;Wagner et al, 2008) in which MbCD enhances, whereas cholesterol inhibits, ion permeation.…”

Why have cholesterol and saturated fatty acids acquired proinflammatory roles during evolution? – A hypothesis from atomistic simulations showing sequence-nonspecific stabilization of peptide dimers in lipid raft-like bilayers

“…Besides GPCRs, the ability of cholesterol to modulate activities of several ion channels and transporters, including Na+, K+-ATPase, is well-established, as discussed in Lange et al [5]. For Kir2 and heterotetrameric Kir3.1/ Kir3.4 channels, specific mutations abrogated cholesterol's effects, supporting the concept of direct binding by cholesterol to a specific site of such channels [11]. Although in some cases (dopamine transporter of Drosophila melanogaster, and Na+, K+-ATPase from pig kidney), the cholesterol binding site was identified by crystallographic analysis, the involvement of indirect effects cannot be excluded from the observed physiological effects of cholesterol.…”