Cholesterol Antagonizes Ethanol Potentiation of Human Brain BK_Ca Channels Reconstituted into Phospholipid Bilayers

Abstract

The activity of large conductance, Ca 2ϩ -sensitive K ϩ (BK Ca ) channels, known to control neuronal excitability, is increased by ethanol (EtOH) exposure. Moreover, brain cholesterol (CHS) is elevated after chronic exposure to EtOH, suggesting that membrane CHS may play a role in drug tolerance. Here, we use BK Ca channels from human brain (hslo subunits), reconstituted into 1-palmitoyl-2-oleoyl phosphatidylethanolamine/1-palmitoyl-2-oleoyl phosphatidylserine (POPS) bilayers, to examine CHS modulation of EtOH sensitivity. Acute exposure to clinically relevant EtOH levels increases channel activity without modifying conductance. In this minimal system, increases in CHS content within the range found in neuronal membranes lead to progressive antagonism of EtOH action. Furthermore, CHS inhibits basal channel activity with an affinity similar to that of CHS blunting of the alcohol effect. Modification of channel gating by either EtOH or CHS is reduced dramatically by removal of POPS from the bilayer, suggesting a common mechanism(s) of action. Indeed, channel dwell-time analysis indicates that CHS and EtOH exert opposite actions on the stability of channel closed states. However, each agent also acts on distinct dwell states not mirrored by the other, which contribute to the opposite effects of CHS and EtOH on channel gating.

TLR4, Ethanol, and Lipid Rafts: A New Mechanism of Ethanol Action with Implications for other Receptor-Mediated Effects

“…If this occurred relatively specifically in lipid rafts, the movement of proteins into or out of rafts or among different raft subpopulations, which is normally part of signaling through several receptor types, could be adversely affected. There is evidence that neurological adaptation (tolerance) to chronic administration of EtOH is associated with increased cholesterol in cell membranes (23), and lipid rafts are enriched in cholesterol compared with the remainder of the membrane. Thus, additional raft microdomains permitted by the presence of additional cholesterol in the membrane may represent additional "targets" for EtOH, so that increasing cholesterol concentration may prevent the effects of EtOH by providing more target sites than EtOH can act to disrupt.…”

Somatic Localization of a Specific Large-Conductance Calcium-Activated Potassium Channel Subtype Controls Compartmentalized Ethanol Sensitivity in the Nucleus Accumbens

“…In addition, they are very sensitive to intracellular calcium, making them well positioned to respond to modifications of the properties of the Ca 2ϩ -permeable NMDA receptor, an ionotropic receptor that is regarded as pivotal in synaptic plasticity in general (Malenka and Nicoll, 1993) and in drug addiction in particular (Trujillo and Akil, 1995). Moreover, BK channels are robustly potentiated by relevant concentrations of ethanol (Dopico et al, 1996;Chu et al, 1998;Knott et al, 2002;Crowley et al, 2003), although one study reported an inhibitory effect on neurons from dorsal root ganglia (Gruss et al, 2001). Finally, recent evidence obtained using Caenorhabditis elegans suggests that the BK channel is the sole mediator of intoxication in this worm model system .…”

BK Channels – Focus on Polyamines, Ethanol/Acetaldehyde and Hydrogen Sulfide (H2S)

“…It appears conceivable therefore that molecules such as cholesterol or alcohol inserted into the membrane bilayer may change its thickness and affect gating of BK channels. In fact elevation of membrane cholesterol decreased channel open probability (Bregestovski et al 1989;Bolotina et al, 1989) and antagonized the potentiating effect of ethanol on BK channels (Crowley et al 2003). Depletion of cholesterol resulted in activation of BK channels, an increase of BK current density and reduced firing of action potentials (Lam et al, 2004;Lin et al, 2006).…”

“…BK channels are generally inhibited by accessory cholesterol in native as well as in reconstituted cell membranes by shortening mean open and extending mean closed times. Depletion of membrane cholesterol results in an increase of channel open probability (Bolotina et al, 1989;Chang et al, 1995b;Crowley et al 2003;Lin et al, 2006;Bukiya et al, 2008).…”