Interaction with stomatin directs human proton channels into cholesterol-dependent membrane domains.

Many membrane proteins are modulated by cholesterol. Here we report profound effects of cholesterol depletion and restoration on the human voltage-gated proton channel, hH1, in excised patches but negligible effects in the whole-cell configuration. Despite the presence of a putative cholesterol-binding site, a CARC motif in hH1, mutation of this motif did not affect cholesterol effects.

Unexpected expansion of the voltage-gated proton channel family.

Voltage-gated ion channels, whose first identified function was to generate action potentials, are divided into subfamilies with numerous members. The family of voltage-gated proton channels (H ) is tiny. To date, all species found to express H have exclusively one gene that codes for this unique ion channel.

Analysis of an electrostatic mechanism for ΔpH dependent gating of the voltage-gated proton channel, H1, supports a contribution of protons to gating charge.

Voltage-gated proton channels (H1) resemble the voltage-sensing domain of other voltage-gated ion channels, but differ in containing the conduction pathway. Essential to the functions of H1 channels in many cells and species is a unique feature called ΔpH dependent gating. The pH on both sides of the membrane strictly regulates the voltage range of channel opening, generally resulting in exclusively outward proton current.

The Chemical Potential of Plasma Membrane Cholesterol: Implications for Cell Biology.

Cholesterol is abundant in plasma membranes and exhibits a variety of interactions throughout the membrane. Chemical potential accounts for thermodynamic consequences of molecular interactions, and quantifies the effective concentration (i.e.

Raft composition at physiological temperature and pH in the absence of detergents.

Biological rafts were identified and isolated at 37 degrees C and neutral pH. The strategy for isolating rafts utilized membrane tension to generate large domains. For lipid compositions that led only to microscropically unresolvable rafts in lipid bilayers, membrane tension led to the appearance of large, observable rafts.

Lipid peroxides promote large rafts: effects of excitation of probes in fluorescence microscopy and electrochemical reactions during vesicle formation.

Raft formation and enlargement was investigated in liposomes and supported bilayers prepared from sphingomyelin (SM), cholesterol, and unsaturated phospholipids; NBD-DPPE and rhodamine-(DOPE) were employed as fluorescent probes. Rafts were created by lowering temperature. Maintaining 20 mol % SM, fluorescence microscopy showed that, in the absence of photooxidation, large rafts did not form in giant unilamellar vesicles (GUVs) containing 20 or more mol % cholesterol.

Effect of chaotropic anions on the sodium transport by the Na,K-ATPase.

The effect of choline iodide, bromide and chloride on the kinetics of the electrogenic sodium transport by the Na,K-ATPase was investigated in a model system of ATPase-containing membrane fragments adsorbed on the lipid bilayer membrane. The kinetic parameters of Na(+) transport were determined from short circuit currents after fast release of ATP from its caged precursor. The falling phase of the current transients could be fitted by a single exponential with the time constant, tau (2).