Exchange of HCO3- for monovalent anions across the human erythrocyte membrane

Characterization of oxalate transport by the human erythrocyte band 3 protein

This paper describes characteristics of the transport of oxalate across the human erythrocyte membrane. Treatment of cells with low concentrations of H2DIDS (4,4'-diisothiocyanatostilbene-2,2'-disulfonate) inhibits Cl(-)-Cl- and oxalate-oxalate exchange to the same extent, suggesting that band 3 is the major transport pathway for oxalate. The kinetics of oxalate and Cl- self-exchange fluxes indicate that the two ions compete for a common transport site; the apparent Cl- affinity is two to three times higher than that of oxalate. The net exchange of oxalate for Cl-, in either direction, is accompanied by a flux of H+ with oxalate, as is also true of net Cl(-)-SO4(2-) exchange. The transport of oxalate, however, is much faster than that of SO4(2-) or other divalent anions. Oxalate influx into Cl(-)-containing cells has an extracellular pH optimum of approximately 5.5 at 0 degrees C. At extracellular pH below 5.5 (neutral intracellular pH), net Cl(-)-oxalate exchange is nearly as fast as Cl(-)-Cl- exchange. The rapid Cl(-)-oxalate exchange at acid extracellular pH is not likely to be a consequence of Cl- exchange for monovalent oxalate (HOOC-COO-; pKa = 4.2) because monocarboxylates of similar structure exchange for Cl- much more slowly than does oxalate. The activation energy of Cl(-)-oxalate exchange is about 35 kCal/mol at temperatures between 0 and 15 degrees C; the rapid oxalate influx is therefore not a consequence of a low activation energy. The protein phosphatase inhibitor okadaic acid has no detectable effect on oxalate self-exchange, in contrast to a recent finding in another laboratory (Baggio, B., L. Bordin, G. Clari, G. Gambaro, and V. Moret. 1993. Biochim. Biophys. Acta. 1148:157-160.); our data provide no evidence for physiological regulation of anion exchange in red cells.

Evidence for two conductance/exchange pathways for chloride in rat parotid secretory granules

Electron probe x-ray microanalysis was used to determine that bromide is localized to rat parotid secretory granules at early stages of an in situ Cl/Br washout experiment. Chloride efflux and bromide influx across the secretory granule membrane occurred with a time order of minutes. Since the Cl washout data indicated minimal Cl binding within the granule, and therefore minimal Br binding, the Br localization results suggest the presence of two or more anion conductance/exchange pathways in the granule membrane for the Cl (Br) ion.

Interactions of bromide, iodide, and fluoride with the pathways of chloride transport and diffusion in human neutrophils

Isolated human neutrophils possess three distinct pathways by which Cl- crosses the plasma membrane of steady state cells: anion exchange, active transport, and electrodiffusion. The purpose of the present work was to investigate the selectivity of each of these separate processes with respect to other external halide ions. (a) The bulk of total anion movements represents transport through an electrically silent anion-exchange mechanism that is insensitive to disulfonic stilbenes, but which can be competitively inhibited by alpha-cyano-4-hydroxycinnamate (CHC; Ki approximately 0.3 mM). The affinity of the external translocation site of the carrier for each of the different anions was determined (i) from substrate competition between Cl- and either Br-, F-, or I-, (ii) from trans stimulation of 36Cl- efflux as a function of the external concentrations of these anions, (iii) from changes in the apparent Ki for CHC depending on the nature of the replacement anion in the bathing medium, and (iv) from activation of 82Br- and 125I- influxes by their respective ions. Each was bound and transported at roughly similar rates (Vmax values all 1.0-1.4 meq/liter cell water.min); the order of decreasing affinities is Cl- greater than Br- greater than F- greater than I- (true Km values of 5, 9, 23, and 44 mM, respectively). These anions undergo 1:1 countertransport for internal Cl-. (b) There is a minor component of total Cl- influx that constitutes an active inward transport system for the intracellular accumulation of Cl- [( Cl-]i approximately 80 meq/liter cell water), fourfold higher than expected for passive distribution. This uptake is sensitive to intracellular ATP depletion by 2-deoxy-D-glucose and can be inhibited by furosemide, ethacrynic acid, and CHC, which also blocks anion exchange. This active Cl- uptake process binds and transports other members of the halide series in the sequence Cl- greater than Br- greater than I- greater than F- (Km values of 5, 8, 15, and 41 mM, respectively). (c) Electrodiffusive fluxes are small. CHC-resistant 82Br- and 125I- influxes behave as passive leak fluxes through low-conductance ion channels: they are nonsaturable and strongly voltage dependent. These anions permeate the putative Cl- channel in the sequence I- greater than Br- greater than Cl- with relative permeability ratios of 2.2:1.4:1, respectively, where PCl approximately 5 X 10(-9) cm/s.

Inorganic carbon transport in biological systems

1. The flux of inorganic carbon (Ci) is an important biological process. 2. CO2 crosses membranes through passive diffusion and, perhaps active transport while HCO3- crosses membranes via facilitated diffusion and active transport mechanisms. 3. Carbonic anhydrase is ubiquitous and enhances the flux of Ci. 4. Generally, Ci crosses membranes through passive and facilitated diffusion when the flux of Ci, per se, is important and crosses membranes via active transport when cells are regulating their intracellular pH and/or ion levels.

A chloride-bicarbonate exchanging anion carrier in vascular smooth muscle of the rabbit

Cl- efflux into various incubation media (PSS) was studied in pieces of rabbit aortae loaded with 36Cl. Replacement of HCO3-/CO2 by HEPES/O2 in the PSS increased the rate of Cl- efflux by a factor of 2.4. This effect was suppressed in Cl(-)-free PSS containing isethionate, propionate, or benzenesulfonate, but not in NO3(-)-PSS, or Br(-)-PSS. The stimulant effect of HCO3- withdrawal on Cl-efflux was reduced by 140 microM DIDS, but not by 1 mM furosemide. The Cl- efflux was temperature-dependent (Q10 = 2.3-2.5), and it was not affected on depolarisation by high [K+]o. The [Cl-]i of rabbit aorta determined by uptake studies with 36Cl, decreased slightly (by 15%) below controls in PSS containing 140 microM DIDS, but drastically (from 32.6 to 13.5 mM, i.e. by 59%) in PSS containing 1 mM furosemide. Withdrawal of HCO3-/CO2 depolarized rabbit pulmonary artery in standard PSS and in Br(-)-PSS or NO3(-)-PSS, but not in benzenesulfonate-PSS. The pHi of rabbit aorta determined by the distribution of (14C)-DMO, increased in Cl(-)-free PSS containing isethionate or glucuronate. It is concluded that transport mechanisms play a major role in the distribution of Cl- in vascular smooth muscle, and that a membrane anion carrier operates in this tissue which can transport Cl- and HCO3- across the cell membrane. This mechanism seems to be involved in the regulation of pHi. However, the known high [Cl-]i of vascular smooth muscle is rather mediated by the furosemide-sensitive Na-K-Cl cotransport than by this anion carrier.

The role of anion transport in the passive movement of lead across the human red cell membrane

Passive Pb transport across the red cell membrane has been studied by measuring Pb uptake from Pb-buffered solutions into resealed ghosts containing EGTA. Over 90% of Pb uptake occurs by a pathway which is inhibited by drugs which block anion transport. The order of effectiveness is 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid (DIDS) and 4-acetamido-4'-isothiocyanostilbene-2,2'-disulphonic acid (SITS) greater than phloretin greater than furosemide and bumetanide. Ouabain and cytochalasin B are ineffective. This implicates the anion-exchange mechanism in Pb uptake. The rate of Pb uptake by this route is directly proportional to external Pb2+ and HCO3- concentrations, and inversely proportional to the H+ concentration. These findings suggest that Pb transport depends on the formation of PbCO3 in solution. Pb transport depends upon the presence of a second anion. In the presence of HCO3-, the rate is stimulated in the order ClO4- less than NO3- and CH3CO2- less than F- less than Cl- less than Br- less than I-. The temperature dependence of Pb uptake is similar to that of HCO3-(-)Cl- exchange. Changes in membrane potential appear to influence Pb transport. The effects are small and somewhat variable, but in general a negative internal potential accelerates uptake and reduces exit. A positive internal potential reduces uptake and accelerates exit. These results suggest that Pb is transported on the anion exchanger. Exchange of PbCO3 for a monovalent anion best fits the experimental data, although transport of a ternary PbCO3(-)anion- complex is a possibility.

Thermodynamics and membrane processes

This review represents a personal view of membrane thermodynamics. I do not intend to deal at all with the irreversible thermodynamics of membrane mass transfer processes. This aspect has been covered far more competently and completely by other people (Bittar, 1970; Paterson, 1970; Rottenberg, Caplan & Essig, 1970; Mitchell, 1970; Rothschildet al.1980; Oster, Perelson & Katchalsky, 1973; Kedem & Katchalsky, 1958; Schwartz, 1971). The recent review on osmosis by Hill (1979) is a particularly succinct appraisal of a facet of irreversible membrane thermodynamics. Arata & Nishimura (1980) have considered the coupling of electron transfer to vectorial processes in biological membranes.