Taurine efflux is a cell volume regulatory process in proximal renal tubules from the teleost Carassius auratus

Abstract

The potential role of taurine transport associated with volume regulation in renal tissue and isolated proximal renal tubules was studied in the teleost Carassius auratus (goldfish). The cellular taurine content in renal tissue fragments incubated in isosmotic solution (290 mOsm) (7.8 +/- 0.9 (SD) micromol g wet wt(-1)) decreased by 60% following exposure to hyposmotic medium (100 mOsm). The rate coefficient for [14C]taurine efflux in renal tissue and in isolated proximal renal tubules was strongly stimulated following hyposmotically or urea-activated cellular swelling. The stimulated basolateral taurine efflux pathway exhibited channel-like functional characteristics since (a) [14C]taurine influx was stimulated in parallel with the osmolality-dependent taurine efflux and (b) this efflux could not be stimulated by high medium taurine concentrations (40 mM) applied 10 min following the osmolality reduction (trans-stimulation test). Administration of the 5-lipoxygenase inhibitor ETH 615-139 (20 microM) during hyposmotic stimulation inhibited regulatory volume decreases but had no effect on taurine efflux. In addition, hyposmotically induced taurine efflux was slightly but significantly inhibited by the cyclooxygenase inhibitor indomethacin (10 microM). The taurine efflux was also dependent on both extra- and intracellular Ca2+. It is concluded that taurine is likely to coparticipate with KCl as an osmoeffector during RVD in Carassius proximal renal tubule cells. Cellular swelling seems to activate a basolateral taurine transport pathway with functional properties of a channel. This efflux mechanism appears to be partly regulated by Ca2+. Such a transport pathway could play a role in the cell volume regulatory mechanisms participating during transepithelial solute and water transport.

Aquaporin expression and cell volume regulation in the SV40 immortalized rat submandibular acinar cell line

“…The onset and duration of the taurine efflux corresponded well with the volume response. Similar results have been found in other cells [11,15] and are most likely indications of how cells use non-ionic compounds in combating osmotic variations in their external milieus.…”

“…This mechanism is generally a result of KCl, amino acid and water efflux [13,30]. Notably, efflux of the β-amino acid taurine has been found to increase significantly during RVD [10,11,15]. The signal for the RVD-associated KCl efflux varies somewhat from cell type to cell type.…”

Effects of arginine, L-alanyl-L-glutamine or taurine on neutrophil (PMN) free amino acid profiles and immune functions in vitro

“…Alterations in PMN intracellular neutral amino acid concentrations, which were also connected with taurine incubation, may draw attention to its role as an important intracellular osmoregulator (Chen and Kempson, 1995). As expected, increases in intracellular taurine levels decreased intracellular neutral amino acid profiles which may impart osmoprotection to PMN-cells (Horio et al, 1997;Fugelli et al, 1995). Our results suggest that neutral amino acids may interfere with intracellular taurine levels and may, therefore, represent a homeostatic reaction to changes in intracellular osmoregulation (Trachtmann et al, 1998;Law, 1998).…”

Volumetric and ionic responses of goldfish hepatocytes to anisotonic exposure and energetic limitation

“…Because in many cell types K + efflux is an early event mediating the RVD (Häussinger et al, 1994;Fugelli et al, 1995), we tested whether ( 86 Rb + )K + transmembrane fluxes decouple during the first 40 min of incubation under hyposmotic conditions. Results in Figs 5, 6 show that the magnitude of ( 86 Rb + )K + efflux, as well as that of the influx, remained constant in isosmotic as well as in hyposmotic (i.e.…”