No abstract

The regulation of ion transport in bovine tracheal epithelium was studied in vitro. In the absence of exogenous modifiers of ion transport, average values for transepithelial electrical potential difference (psi t), short-circuit-current (Isc) and tissue resistance (Rt) were 35.4 mV (lumen negative), 5.4 muEq X h-1 X cm-2 and 187 omega X cm2 respectively; net Cl secretion (3.2 muEq X h-1 X cm-2) and net Na absorption (1.3 muEq X h-1 X cm2) accounted for 82% of the Isc. Amiloride reduced psi t and Isc, and increased Rt. The values of psi t, Rt and Isc obtained following addition of theophylline, epinephrine or prostaglandin E1 (PGE1) were not different from control values. Theophylline also did not alter Na and Cl fluxes but it increased tissue cAMP content 3-fold. Indomethacin did not affect psi t but it increased Rt and net Na absorption, and decreased Isc and net Cl secretion; it did not significantly reduce tissue cAMP. When added to indomethacin-treated tissues, epinephrine restored Isc, Rt and Na and Cl fluxes to control levels and increased tissue cAMP 3-fold. Similarly, when PGE1 was added to indomethacin-treated tissues, Isc and Rt were restored to control levels.(ABSTRACT TRUNCATED AT 250 WORDS)

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], ...

SUMMARY1. The active transport of Na and Cl across bovine tracheal epithelium was studied in vitro by measuring 22Na and 36CI fluxes under short-circuit conditions.2. Under basal conditions, both net Cl secretion and net Na absorption were observed; the sum of these two net fluxes accounted for 85 % of the measured short-circuit current. The rate of spontaneous C1 secretion exceeded that of Na absorption by a factor of 2.3. Indomethacin, an inhibitor of endogenous prostaglandin production, decreased Cl secretion and increased Na absorption, reversing the direction ofnet transepithelial ion flow from secretion to absorption. The ratio of the change in each net ion flux was about 1:1.4. 50 % of the basal net flux of Na was inhibited by amiloride (10-4 M). The indomethacin-induced increase in the lumen-to-serosa flux of Na was entirely amiloride sensitive. An amiloride-insensitive fraction of this flux, of constant magnitude, was apparent in both control and indomethacin-treated tissues. The Na transport inhibitor had no effect on unidirectional or net Cl fluxes. 5. Cl secretion was abolished by 4-methyl-diphenylamine-2'-carboxylic acid (50B).The C1 transport inhibitor had no effect on unidirectional or net Na fluxes.6. The results suggest that the rates of Na and Cl transport may be modulated in a reciprocal fashion by certain agents, which probably act through cyclic AMP, but that the two transport processes are not mutually interdependent in any simple, direct fashion.7. The lack of evidence for direct interaction between Na and Cl transport raises the possibility that there are separate absorptive and secretary cells in the tracheal epithelium, rather than a single transporting cell.

SUMMARYThe uptake of sodium into vesicles isolated from the microvillous, maternal-facing plasma membrane of human placenta was studied. In equilibrium exchange conditions, sodium entry increased with time towards an equilibrium value after 30-60 min. Over 90 % of the uptake was into an osmotically active space and the initial rate of uptake was halved by amiloride but unaffected by loop diuretics and capnophorin inhibitors. The apparent inhibition constant (K1) for amiloride was 3 5 x 10-6 M and the Michaelis constant (Km) with respect to sodium of the amiloride-sensitive component was 7-11 mm. With an imposed outward H+ gradient, sodium was transiently accumulated within the vesicles. The overshoot was abolished by amiloride and shown, by experiments with FCCP (carbonyl cyanide p-trifluoromethoxyphenylhydrazone) and potassium and valonomycin, not to be dependent on any electrical potential generated by the HI gradient. The evidence for Na+-H+ exchange at this surface and its possible functions are discussed.