title: Transport of H2S and HS(-) across the human red blood cell membrane: rapid H2S diffusion and AE1-mediated Cl(-)/HS(-) exchange.
abstract: The rates of H2S and HS(-) transport across the human erythrocyte membrane were estimated by measuring rates of dissipation of pH gradients in media containing 250 μM H2S/HS(-). Net acid efflux is caused by H2S/HS(-) acting analogously to CO2/HCO3(-) in the Jacobs-Stewart cycle. The steps are as follows: 1) H2S efflux through the lipid bilayer and/or a gas channel, 2) extracellular H2S deprotonation, 3) HS(-) influx in exchange for Cl(-), catalyzed by the anion exchange protein AE1, and 4) intracellular HS(-) protonation. Net acid transport by the Cl(-)/HS(-)/H2S cycle is more efficient than by the Cl(-)/HCO3(-)/CO2 cycle because of the rapid H2S-HS(-) interconversion in cells and medium. The rates of acid transport were analyzed by solving the mass flow equations for the cycle to produce estimates of the HS(-) and H2S transport rates. The data indicate that HS(-) is a very good substrate for AE1; the Cl(-)/HS(-) exchange rate is about one-third as rapid as Cl(-)/HCO3(-) exchange. The H2S permeability coefficient must also be high (>10(-2) cm/s, half time <0.003 s) to account for the pH equilibration data. The results imply that H2S and HS(-) enter erythrocytes very rapidly in the microcirculation of H2S-producing tissues, thereby acting as a sink for H2S and lowering the local extracellular concentration, and the fact that HS(-) is a substrate for a Cl(-)/HCO3(-) exchanger indicates that some effects of exogenous H2S/HS(-) may not result from a regulatory role of H2S but, rather, from net acid flux by H2S and HS(-) transport in a Jacobs-Stewart cycle.
authors.affiliation: Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock, Arkansas.
authors.forename: Michael L
authors.initials: ML
authors.lastname: Jennings
mesh_terms: D001457:Anion Exchange Protein 1, Erythrocyte / Q000502:physiology*; D001692:Biological Transport / Q000502:physiology; D002462:Cell Membrane / Q000378:metabolism*; D004058:Diffusion; D004912:Erythrocytes / Q000378:metabolism*; D006801:Humans; D006862:Hydrogen Sulfide / Q000378:metabolism*
chemical_list: D001457:Anion Exchange Protein 1, Erythrocyte; D006862:Hydrogen Sulfide
keywords: AE1; erythrocyte; hydrogen sulfide; sulfide anion; transport