Taurine secretion in primary monolayer cultures of flounder renal epithelium: stimulation by low osmolality

Abstract

Transepithelial taurine fluxes determined in short-circuited monolayer cultures of flounder renal proximal cells in Ussing chambers revealed net taurine secretion. Both unidirectional secretory and reabsorptive taurine fluxes exhibited saturation kinetics contributed by two distinct saturable transepithelial taurine transport systems operating at different taurine concentration ranges. The taurine secretory system operating below 0. 5 mM had lower affinity but higher capacity than the reabsorptive system, whereas the one operating at high concentrations (0.5-3.0 mM) had higher affinity but the same capacity as the corresponding reabsorptive system. Exposure (2 h) of the cultures to hyposmotic medium in the presence of taurine increased taurine secretory flux twofold with no effect on the reabsorptive flux. The hyposmolality-induced increase in taurine secretion was associated with a decreased peritubular taurine efflux and a concurrent increased luminal taurine efflux; the latter occurred via a pathway that was not affected by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid but inhibited by probenecid. The culture response in hyposmotic medium mimics the in vivo response of the intact marine fish kidney to dilution.

Swelling-activated transport of taurine in cultured gill cells of sea bass: physiological adaptation and pavement cell plasticity

“…Therefore, the hypotonically activated taurine transport pathways are distributed in a polarized way in gill cells. Similar findings have been observed in goldfish renal cells (14) and in amphibian A6 cells (51) but not in flounder renal cells (7). The increased gill secretion of taurine through the apical membrane in a diluted environment will help the fish excrete any excess of osmotically active material and obligated water more rapidly, thus facilitating the RVD, as observed by Benyajati and Renfro (7) in flounder renal tubules.…”

“…Investigators have reported that physiological concentrations of plasma taurine increased from 0.1-0.8 mM to 1.3-2.5 mM when marine fish were transferred from isosmotic to hyposmotic conditions (7). We suggest that the high rate of taurine secreted into the circulation (i.e., at the basolateral side) may contribute to the restoration of plasma osmotic pressure in fish, but this effect will need to be further investigated.…”

“…In most marine organisms, cells contain large concentrations of taurine and other organic osmolytes that fill the osmotic gap between external and internal ion concentrations. Intracellular taurine concentrations are known to range from 20 to 65 mM in various fish (7,22,38).…”

Regulatory volume decrease and P receptor signaling in fish cells: mechanisms, physiology, and modeling approaches

“…Taurine efflux was also found to be important in the RVD response of many other models, e.g. in teleost heart ventricular cells (Vislie, '83), dogfish shark ( S. acanthias ) rectal gland cells (Ziyadeh et al, '88), trout hepatocytes (Michel et al, '94), goldfish renal proximal tubules (Fugelli et al, '95), winter flounder ( Pleuronectes americanus ) renal cells (Benyajati and Renfro, 2000), walking catfish ( Clarias batrachus ) liver (Goswami and Saha, 2006), and sea bass gill cells (Avella et al, 2009). Regulation of taurine release includes control by external Ca 2+ (trout hepatocytes; gill cells, goldfish proximal renal tubules) and prostaglandin synthesis (Fugelli et al, '95), but further characterization of control mechanisms still awaits investigation.…”

Phototrophic utilization of taurine by the purple nonsulfur bacteria Rhodopseudomonas palustris and Rhodobacter sphaeroides

“…In marine habitats, for example, a diverse group of organisms such as algae, oysters, mussels, copepods, diatoms, vestimentiferan worms and flounder utilize taurine as an osmolyte (Benyajati & Renfro, 2000;Burton & Feldman, 1982;Jackson et al, 1992;Pierce et al, 1992;Sansone et al, 1987;Walther, 2002;Yin et al, 2000). While sulfonate compounds are found in many environments, many eukaryotic organisms are unable to attack the carbonsulfur bond.…”