Biomedical subjects
Publications and source records attributed to M Raida.
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Murine band 3 protein was expressed in oocytes of Xenopus laevis after microinjection of the mRNA from the spleens of anemic mice. The 36Cl- efflux from the oocytes was compared with the chloride fluxes measured in murine red cells. In both oocytes and red cells, the band 3-mediated chloride transport showed the following features: the selective inhibitor of band 3-mediated anion transport, 4,4'-dinitrostilbene-2,2'-disulfonate exerts its effects only when applied to the outside and not when applied to the inside of the membrane. The K1/2 for inhibition by external 4,4'-dinitrostilbene-2,2'-disulfonate was of the order of 1.5 to 2.0 mumol/l. Flufenamate and persantine also produce similar inhibitory effects. Decreasing the pH from 7.4 to 6.0 leads to some inhibition. It is concluded that essential features of the mode of action of murine erythroid band 3 protein in the plasma membrane of the oocyte are similar to the mode of action in the bilayer of the red blood cell of the mouse.
Dansylation of the red blood cell membrane inhibits monovalent anion transport as measured by means of 36C1 and enhances divalent anion transport as measured by means of 35SO4 (Legrum, Fasold and Passow (1980) Hoppe-Seyler's Z. Physiol. Chem. 361, 1573-1590 and Lepke and Passow (1982) J. Physiol. (London) 328, 27-48). In the present work the effect of dansylation on phosphate equilibrium exchange was studied over the pH range where the ratio between monovalent and divalent phosphate anions varies. At high pH, phosphate equilibrium exchange was enhanced; at low pH, exchange was inhibited. The pH maximum of phosphate equilibrium exchange, seen at pH 6.3 in untreated ghosts is now replaced by a plateau. The inverse effects of dansylation on the rates of exchange at high and low pH suggest that both monovalent and divalent phosphate anions are accepted as substrates by the anion transport protein. A tentative attempt to obtain a quantitative estimate of the ratio of monovalent and divalent phosphate transport indicates that in the untreated red cell membrane over the pH range 7.2-8.5 the transport of HPO42- is negligible compared to the transport of H2PO4-.
Sulfate transport across the red cell membrane is enhanced by the newly synthesised, water-soluble and nonpenetrating dansyl chloride derivative 2-(N-piperidine)ethylamine-1-naphthyl-5-sulfonylchloride (PENS-Cl). The transport is only enhanced if the potentiating agent 2-(4-aminophenyl-3-sulfonic acid)-6-methylbenzothiazol-7-sulfonic acid (APMB) is present during incubation with PENS-Cl. The enhanced flux is reduced by the anion-transport inhibitor 4,4'-diisothiocyanatodihydrostilbene-2,2'-disulfonate (H2DIDS) to about the same low level as in untreated controls. In contrast to dansyl chloride, PENS-Cl does not increase cation leakage from the red cells. The effects of PENS-Cl on sulfate transport resemble those produced by dansyl chloride. However, it can be shown that PENS-Cl only reacts with one subset of sites that are modified by dansyl chloride and involved in bringing about the enhancement of sulfate transport. This subset does not include the sites accessible to dansyl chloride in the absence of APMB. It comprises only a fraction of the sites exposed to dansyl chloride in the presence of APMB. Very little labelling of proteins of the red cell membrane can be seen after exposure of ghosts to the PENS-Cl, while dansyl chloride labels all major proteins.
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