Transepithelial transport and cell volume control in proximal renal tubules from the teleost Carassius auratus

The objective of this work was to study cell volume regulation and transepithelial transport in renal proximal tubules. A modified stop-flow technique in in vitro perfused renal proximal tubules of Carassius auratus was used. The rate of luminal fluid absorption and the epithelial thickness were measured. Isosmotic Na+ removal from the tubule lumen or addition of the Na+/glucose co-transport blocker phloridzin (0.5 mM) to the lumen inhibited fluid absorption. Only minor effects on luminal absorption were observed following. (1) addition of the K+ channel inhibitor BaCl2 (1 mM); (2) addition of the Cl- channel inhibitor MK-196 (1 mM); (3) lowering bath and perfusate HCO3- in the presence of 0.1 mM acetazolamide; or (4) addition of the leukotriene-D-4, receptor antagonist L-660, 711 (20 mu M). Isosmotic addition of 40 mM taurine to the bath inhibited the rare of fluid absorption. This effect could be partially overcome with the organic acid secretion inhibitors probenecid (1 mM) and bromcresol green (0.1 mM). Finally, administration of the 5-lipoxygenase antagonist ETH 615-139 (20 mu M) caused a significant reduction in the rate of luminal absorption. In summary, tubular reabsorption is, in this preparation, closely linked to sodium reabsorption. In the absence of luminal amino acids most of this sodium uptake seems to occur in co-transport with glucose followed by osmotically obligated water. Eicosanoids from the 5-lipoxygenase pathway appear to regulate this process. Finally, high concentrations of taurine in the bath opposed luminal fluid absorption, at least partially, by its secretion into the tubular lumen.