Sulfate transport in rabbit ileum: Characterization of the serosal border anion exchange process

Abstract

The preceding paper [30] shows that transepithelial ileal SO4 transport involves Na-dependent uptake across the ileal brush border, and Cl-dependent efflux across the serosal border. The present study examines more closely the serosal efflux process. Transepithelial mucosa (m)-to-serosa (s) and sto-m fluxes (Jms, Jsm) across rabbit ileal mucosa were determined under short-circuit conditions. SO4 was present at 0,22 mM. In standard C1, HCO3 Ringer's, jso4 was 81.3 +5.3 (1SE) and jso4 was 2.5_+0.2 nmol cm-2hr-l(n=20). Serosal addition of 4-acetamido-4'-isothiocyanostilbene-22'-disulfonate (SITS), 44'-diisothiocyanostilbene-22'-disulfonate (DIDS) or 1-anilino-8-naphthalene-sulfonate (ANS) inhibited SO4 transport, SITS being the most potent. Several other inhibitors of anion exchange in erythrocytes and other cells had no effect on ileal SO4 fluxes. In contrast to its effect on SO4 transport, SITS (500 gM) did not detectably alter C1 transport.Replacement of all C1, HCO3 and PO~ with gluconate reduced jso4 by 70% and increased jso4 by 400%. A small but significant I s~ remained, lso4 vnet ~ms could be increased by addition to the serosal side of C1, Br, I, NO3 or SO4. The stimulatory effect of all these anions was saturable and SITS-inhibitable. The maximal jso4 in the presence of C1 was considerably higher than in the presence of SO4 (73.1 and 42.2nmol cm -2 hr -t, respectively; p<0.001). The K~ value for C1 was 7.4 mM, 10-fold higher than that for SO4 (0.7 mM). Omitting HCO3 and PO4 had no measurable effects on SO4 fluxes.This study shows that (i) SO4 crosses the serosal border of rabbit ileal mucosa by anion exchange; (i 0 the exchange process is inhibited by SITS, DIDS and ANS, but not by several other inhibitors of anion exchange in other systems; (iii) SO4 may exchange for C1, Br, I, NO3 and SO4 itself, but probably not for HCO3 or PO~; (iv) kinetics of the exchange system suggest there is a greater affinity for SO4 than for C1, although the maximal rate of exchange is higher in the presence of C1; and, finally (v) SITS has little or no effect on net C1 transport.The preceding paper [30] shows that active SO4 absorption in rabbit ileum involves two separate steps: (0 a Na-dependent uptake at the brush border, and (ii) a Cl-dependent efflux at the serosal border. The latter can be blocked by the stilbene derivatives 4-acetamido-4'-isothiocyanostilbene-2,T-disulfonate (SITS) 1 and 4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS), which are potent inhibitors of anion exchange in both erythrocytes [5] and Ehrlich ascites tumor cells [22,23]. In the present study, we further investigate the serosal border component of SO4 transport in rabbit ileum. Transepithelial mucosa (m)-to-serosa (s) and s-to-m fluxes of SO4 were determined under short-circuit conditions in Ringer's solutions of different anionic compositions. The effects of a number of anion transport inhibitors were also tested. For most flux measurements, the SO~ concentration was set at 0.22 mM, or about 10-fold lower than in the preceding study [30], ...

Effects of acid-base variables on ion transport in rat colon.

“…In recent studies of the rat proximal and distal colon, however, 2 mM mucosal DIDS and 1 mM 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid did not alter J", Jcn,' or Isc despite other evidence suggesting that anion exchange was present (18, 28). Similar observations have been made in rabbit ileum (29) and rabbit colon (30). Our results therefore do not absolutely exclude the participation of Cl/HCO3 ion exchange in the rat distal colon's response to CO2.…”

Renal sulfate transport at the basolateral membrane is mediated by anion exchange.

“…After accumulation within the cell, sulfate may exit at the luminal face of the cell in exchange for bicarbonate or another anion (4). The luminal anion exchanger is similar to exchangers described in other tissues except that its affinity for chloride apparently is much lower (5)(6)(7)(8)(9)(10).…”

“…SITS, a widely used inhibitor of anion exchange in other systems, abolished the bicarbonate stimulation of sulfate uptake. Phloretin, which also inhibits anion exchange in several systems (10), was an effective (=70%) inhibitor. Thiosulfate, presumably a competitor for the sulfate site (13,18,19), also virtually eliminated the HCOj stimulation of sulfate uptake at 15 sec.…”

“…5 summarizes the effects of several potential inhibitors on HCO-/SO2-exchange. Mercury, a relatively nonspecific inhibitor of carrier-mediated transport (27), inhibited sulfate uptake by 50% (at 10 ,uM) to 90% (at 100 ,M) at 15 sec. SITS, a widely used inhibitor of anion exchange in other systems, abolished the bicarbonate stimulation of sulfate uptake.…”

Anion Transport and 2,3-Diphosphoglycerate in Cystic Fibrosis Red Blood Cells

“…In various other types of cells, a saturable anion transport can be found that can also be inhibited by stilbene disulfonates. For example, in Ehrlich ascites tumor cells (2 I) and rabbit ileum (19), sulfate transport can be strongly inhibited by these compounds, whereas chloride transport is almost unaffected. Active chloride transport in the amphibian cornea is inhibited on both the aqueous and tear side of the cells by DIDS (2).…”