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Linear alkylbenzene sulfonate (LAS) is found in near-shore environments receiving wastewater from urban treatment plants in a concentration reported to have physiological and toxic effect on aquatic organisms. The aim of this study was to investigate the effect LAS on ion transport and homeostasis in epithelia cells. A6 cells form a polarised epithelium when grown on permeable supports, actively absorb sodium and secrete chloride. Only the addition of LAS (100 microM) to the apical solution of A6 epithelia resulted in an increase in the active ion transport measured as short circuit current (SCC) and transepithelial conductance (G(t)). This increase could not be affected by the sodium channel inhibitor amiloride (100 microM), indicating that LAS stimulated the chloride secretion. Change in the intracellular calcium concentration (Ca(2+))(i) was measured in fura-2 loaded A6 cells, since it known that increase in (Ca(2+))(i) stimulate chloride secretion. LAS induced a concentration-dependent increase in (Ca(2+))(i) from 5 to 200 microM, where the half-maximal stimulating concentration on 100 mM resulted in an increase in (Ca(2+))(i) from 108+/-15 to 570+/-26 nM (n=4; P

The effect of Cd(2+) on chloride secretion was examined in A6 renal epithelia cells by chloride-sensitive fluorescence (SPQ probe) and by the short-circuit-current (I(sc)) technique. Depleting the cells of Cl(-) suggests that the Cd(2+)-activated I(sc) (DeltaI(sc(Cd))) is dependent on the presence of Cl(-) ions. Among the Cl(-)-channel inhibitors the fenemates, flufenamic acid (FFA) and niflumic acid (NFA), and 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB) significantly lowered DeltaI(sc(Cd)) compared with control level. In SPQ-loaded A6 cells, Cd(2+) evoked an increase in Cl(-) secretion ([DeltaCl(-)](Cd)), which significantly exceeded the basal Cl(-) transport and was blockable by FFA and NFA. The closely related metals, Zn(2+) or Ni(2+), were also able to activate Cl(-) secretion. Preexposure of Zn(2+) or Ni(2+) completely prevented [DeltaCl(-)](Cd), suggesting that Zn(2+) and Ni(2+) probably use similar mechanisms. Like Cd(2+), thapsigargin (TG), an inhibitor of intracellular Ca(2+)-ATPase and the Ca(2+)-ionophore A23187, induced an increase in I(sc). Moreover, TG and Cd(2+) were able to neutralize the responses of the counterparts as also observed in I(sc) measurements, which indicates that Cd(2+) activates Cl(-) secretion in a Ca(2+)-dependent manner. Hence, this study supports the idea that basolateral Cd(2+) (possibly also Zn(2+) and Ni(2+)), probably through a Ca(2+)-sensing receptor, causes calcium mobilization that activates apical fenemate-sensitive chloride channels leading to chloride secretion in A6 cells.

Cisplatin is a platinum-containing antitumour agent, the usefulness of which is limited by nephrotoxicity. In the present study, we examined the effects of cisplatin on the established renal epithelial A6 cell line, which forms a polarized monolayer in vitro with active transmembrane ion transport. The effect of cisplatin (0–800 μ m ) on transepithelial ion transport and transepithelial resistance (TER) was monitored by the short-circuit current (SSC) technique. Cell integrity was determined by monitoring TER at increasing concentration of cisplatin during 24 hours. The half-maximal inhibition concentration was 49 and 540 μ m when applied to either the basolateral or apical surface, respectively. This suggests that cisplatin-mediated deterioration of cell integrity is far more pronounced when cisplatin is applied basolaterally than apically. Continuous measurements of TER demonstrated a dose- and time-dependent decline in TER/TER0 (TER at time zero). In addition, cisplatin from the basolateral side had no prompt effect on transepithelial ion transport. Instead a slow, but dose-dependent decline which at the highest concentration resembled the decline observed when ouabain was added. Inhibition of Na-K-ATPase by cisplatin was examined by the use of nystatin, a membrane permeabilizer, and data suggest that cisplatin at 800 μ m inhibits Na-K-ATPase by about 50% after 60 minutes of exposure. Morphological examinations of subcultured cisplatin treated cells indicate that cell death is probably due to apoptosis rather than necrosis.

1. 1. The role of prostaglandins and intracellular Ca 2+ in regulation of active transepithelial sodium transport in frog skin were studied by examinations of effects of the calcium ionophore A23187 on short-circuit current (SCC) and intracellular voltage. 2. 2. A23187 and arachidonic acid induced a marked increase in both SCC and prostaglandin E 2 synthesis. 3. 3. In indomethacin treated skins A23187 did not stimulate but on the contrary inhibited the basal SCC. 4. 4. The A23187-induced increase in SCC was associated with a decrease in the fractional resistance of the apical membrane and a depolarization of the cells. 5. 5. In skins pretreated with indomethacin, the A23187 induced inhibition of SCC coincided with a slight hyperpolarization of the cellular potential and an increase in fractional resistance of the apical membrane.