Water cotransport in pigmented epithelial cells.

摘要

Zeuthen and his group deserve high praise for their dogged challenge to the dogma that water moves across cell membranes only passively as a result of osmotic and hydrostatic pressure gradients. Instead, in an article in this issue of The Journal of Physiology, they maintain that water can also be cotransported along with solutes via cotransporters (Hamann et al. 2010). Two options were originally suggested to explain this process; water was either cotransported along with ions and solutes, e.g. glucose and Na~+, through the sodium-glucose cotransporter, SGLT1, via a carrier complex, access to which alternated between the two sides of the membrane. The force generating water flow is assumed to be the resultant of the combined chemical potential gradients of the cotransported components within the complex. Alternatively, it was suggested that the cotransported water was generated by osmosis from solute gradients acquired within a discrete membrane compartment (Zeuthen & Stein, 1994).