Further evidence for the existence of a volume‐activated taurine efflux pathway in rat mammary tissue independent from volume‐sensitive Cl^– channels

Abstract

The effect of cell-swelling, induced by a hyposmotic shock, on the fractional loss of taurine, D-aspartate and iodide from lactating rat mammary tissue explants has been examined. In paired experiments, cell-swelling markedly increased the fractional efflux of taurine but not that of D-aspartate. Similarly, in paired experiments, a hyposmotic challenge stimulated taurine release but not iodide efflux. The results suggest that volume-activated taurine efflux from mammary tissue explants is via a pathway independent from volume-sensitive anion channels. It is apparent that the volume-activated taurine efflux pathway in mammary tissue is not the volume-sensitive organic osmolyte-anion channel which has been described in other cells. Therefore, the results of this study together with others in the literature constitute prima facie evidence for the existence of more than one type of swelling-activated pathway which accepts taurine as a substrate.

Receptor Regulation of the Volume-Sensitive Efflux of Taurine and Iodide from Human SH-SY5Y Neuroblastoma Cells: Differential Requirements for Ca2+ and Protein Kinase C

“…Similarities in the pharmacological inhibition profile of swelling-activated efflux of organic osmolytes and Cl Ϫ in response to anion channel blockers has led to the suggestion that a common pathway exists for the extrusion of both Cl Ϫ and organic osmolytes (Banderali and Roy, 1992;Jackson and Strange, 1993;SanchezOlea et al, 1996;Abdullaev et al, 2006). However this possibility is at variance with results obtained from some nonneural tissues in which Cl Ϫ and taurine effluxes were found to exhibit differences in kinetics of release, osmotic sensitivity, and/or the degree of inhibition by anion channel blockers, results which suggest the existence of separate volume-sensitive channels for Cl Ϫ and organic osmolytes (Lambert and Hoffmann, 1994;Davis-Amaral et al, 1996;Shennan et al, 1996;Stutzin et al, 1999;Shennan and Thomson, 2000;Tomassen et al, 2004).…”

“…However, in some tissues, the existence of separate Cl Ϫ and taurine efflux pathways has also been proposed (Lambert and Hoffman, 1994;Stutzin et al, 1999;Shennan and Thomson, 2000;Tomassen et al, 2004). In addition, the issue of whether Cl Ϫ and organic osmolytes are released from the cell under conditions of receptor activation via shared or distinct pathways has not yet been systematically addressed.…”

Organic Osmolyte Channels: A Comparative View

“…Shennan and coworkers have presented evidence that in rat mammary tissue osmotic swelling induces the efflux of taurine while having little effect on the efflux of either I -or D-aspartate [36,37]. In another recent study Bröer and colleagues report that in Xenopus oocytes expressing different exogenous proteins, exposure to hypoosmotic media stimulates an efflux of taurine, while having little effect on either the efflux of 36 …”

Cloning of rabbit Kir6.1, SUR2A, and SUR2B: possible candidates for a renal KATP channel

“…If taurine can be shown to be an exportable osmolyte in PCT as for other tissues (15,28,34,40), a PCT cell that is initially swollen by excessive apical Na ϩ uptake could react by releasing its intracellular taurine. This decrease in intracellular taurine concentration would activate basolateral K ATP channels.…”

“…The voltage range covered was from Ϫ165 to ϩ85 mV. Three different bath solutions were used: 1) a modified Barth's solution (M-Barth) that contained (in mM) 40 …”