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 tra nsepithelial transport in renal proximal tubules. A modified stop-flow technique in in vitro perfused renal proximal tubules of Carassius au ratus was used. The rate of luminal fluid absorption and the epithelia l thickness were measured. Isosmotic Na+ removal from the tubule lumen or addition of the Na+/glucose co-transport blocker phloridzin (0.5 m M) to the lumen inhibited fluid absorption. Only minor effects on lumi nal 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 t o the bath inhibited the rare of fluid absorption. This effect could b e partially overcome with the organic acid secretion inhibitors proben ecid (1 mM) and bromcresol green (0.1 mM). Finally, administration of the 5-lipoxygenase antagonist ETH 615-139 (20 mu M) caused a significa nt reduction in the rate of luminal absorption. In summary, tubular re absorption is, in this preparation, closely linked to sodium reabsorpt ion. In the absence of luminal amino acids most of this sodium uptake seems to occur in co-transport with glucose followed by osmotically ob ligated water. Eicosanoids from the 5-lipoxygenase pathway appear to r egulate this process. Finally, high concentrations of taurine in the b ath opposed luminal fluid absorption, at least partially, by its secre tion into the tubular lumen.