Effects on Membrane Permeability

Inhaled anesthetics increase the flow of cations and protons across lipid vesicles.^[121] It has been suggested that anesthetics may act by increasing proton permeability across synaptic vesicles, collapsing the pH gradient required for retention of catecholamines in their charged form and thereby depressing neurotransmission by releasing catecholamines from synaptic storage vesicles. However, this hypothesis seems unlikely because marked depletion of brain catecholamines lowers the MAC by a maximum of 40%, clinical concentrations of inhaled agents release only a small fraction of catecholamines trapped in vesicles, and not all anesthetics increase proton conduction across lipid vesicles.^[121]