Molecular characterization of mouse monoclonal antibody BIII.136 and the epitope recognized by the antibody in human band 3 protein

Molecular characterization of anion exchangers in the cochlea

Anion exchange proteins (AE) in the inner ear have been the focus of attention for some time. They have been suggested to play a role as anion exchangers for the regulation of endolymphatic pH or as anion exchangers and anchor proteins for the maintenance of the shape and turgor of outer hair cells, and they also have been discussed as a candidate protein for motile hair cell responses that follow high-frequency stimulation. The existence of anion exchangers in hair cells and the specific isoforms which are expressed in hair cells and the organ of Corti is controversial. Using a polyclonal antibody to AE1 (AB 1992, Chemicon), we immunoprecipitated a 100 kDa AE polypeptide in isolated outer hair cells which, due to its glycosylation, is comprised of AE2 than AE1 isoforms. We confirmed AE2 expression in outer hair cells with the help of subtype-specific monoclonal and polyclonal antibodies to AE, AE subtype-specific primers and AE subtype-specific cDNA and found glycosylated truncated as well as full-length AE2 isoforms. No AE1 or AE3 subtypes were noted in outer hair cells. In contrast, AE2 and AE3 but not AE1 subtypes were seen in supporting cells of the organ of Corti. Their expression preceded the development of cochlear function, coincident with the establishment of the endocochlear potential and the differentiation of supporting cells. While most developmental processes in the inner ear usually begin in the basal cochlear turn, the AE2 expression in outer hair cells (but not that of AE2 and AE3 in supporting cells) progressed from the apical to the basal cochlear turn, reminiscent of the maturation of frequency-dependency. Irrespective of their presumed individual role as either anion exchanger, anchor protein or motility protein, the differential expression and developmental profile of these proteins suggest a most important role of anion exchange proteins in the development of normal hearing. These findings may also provide novel insights into AE function in general.

Chloride transport across syncytiotrophoblast microvillous membrane of first trimester human placenta

There are significant changes in the activity of some placental transporters between first trimester and term. However, chloride transport has previously been studied only in the term placenta. Therefore. in this study, we investigated chloride transport mechanisms in syncytiotrophoblast microvillous membrane (MVM) vesicles from first trimester human placentas and compared them with those in vesicles from term placentas. 36Cl- uptake into MVM vesicles was linear up to 45 s and had reached equilibrium by 1 h for both first trimester and term vesicles. In first trimester MVM at 0 mV, 0.1 mM diisothiocyano-2,2'-disulfonic stilbene (DIDS) blocked 25+/-3% (n=8) of 36Cl- uptake at 30 s (initial rate), which was similar to the 30+/-7% (n=6) inhibition by DIDS in term MVM. In the presence of a 25 mV inside-positive electrical potential difference, induced by imposition of a K+ gradient after preincubation with 200 microM valinomycin, 0.5 mM diphenylamine-2-carboxylate (DPC) significantly blocked 30+/-4% of 36Cl- uptake at 30 s by first trimester MVM (p < 0.01); 18+/-5% (n=8) of total uptake was inhibited by DPC but not by DIDS. There was a similar 15+/-3% (n=6) component of 36Cl- uptake by term MVM, which was inhibited by DPC but not by DIDS. Using Western blotting, it was shown that the anion exchanger-1 protein was expressed in first trimester MVM in quantitatively similar amounts to that in term MVM. This study suggests that there is both an anion exchanger and a DPC-sensitive conductance in MVM of first trimester placenta with activity similar to that of term human placenta.

beta-Elimination of O-glycans from glycoproteins transferred to immobilon P membranes: method and some applications

Selective beta-elimination of O-glycans from glycoproteins transferred from electrophoretic gels onto Immobilon P membranes is described. The experiments were performed with erythrocyte membrane proteins, in which glycophorins are the major poly-O-glycosylated components, and with lysates of human colon cancer cells CX-1.1. Lectins and monoclonal antibodies against peptidic, glycopeptidic, and carbohydrate epitopes were used to examine the effect of degradation. Experiments with erythrocyte membrane proteins showed that after heating the blots in 0.055 M NaOH for 16 h at 40 degrees C the O-glycans of glycophorins were undetectable, while N-glycans and peptidic epitopes of proteins were detected with unchanged or even increased intensity compared to untreated blots. The method was used to show that most protein-linked sialyl-Lea epitopes present on CX-1.1 cancer cells are located on O-glycosidic chains. Moreover, beta-elimination on the blots allows examination of the dependence of peptidic epitopes on O-glycosylation. This was shown using monoclonal antibodies specific for blood group M- or N-related epitopes of glycophorin A (GPA). Most of these antibodies recognize glycopeptidic epitopes dependent on O-glycosylation and, therefore, they did not detect GPA on NaOH-treated blots. Some less frequent anti-M antibodies cross-reacting with the rare GPA variant of Mg type are specific for a peptidic epitope which is unrelated to the MN blood group-specific amino acid sequence in unglycosylated peptides, but is recognized in GPA-M only in the glycosylated antigen. These antibodies, which showed specificity for GPA-M on untreated blots, detected GPA-M, GPA-N, and glycophorin B on NaOH-treated blots.