Volume-activated taurine efflux from the in situ perfused lactating rat mammary gland.

The effect of cell swelling on the efflux of amino acids from the in situ perfused lactating rat mammary gland has been examined. Cell swelling, induced by a hyposmotic shock, increased the fractional release of [3H]taurine. In contrast, a hyposmotic shock did not stimulate the efflux of D-[3H]aspartate, suggesting that the effect of a hyposmotic challenge on taurine release cannot be attributed to cell lysis. Volume-activated taurine efflux was reversible, dependent upon the extent of the osmotic challenge and inactivated with a prolonged hyposmotic shock. The release of taurine was also reversibly increased following isosmotic cell swelling (using urea). The results confirm the presence of a volume-sensitive taurine efflux transport system in lactating rat mammary tissue and suggest that the volume-activated amino acid efflux pathway is located at the blood-facing aspect of the mammary epithelium.