Passive water and ion transport by cotransporters.

摘要: 1 The rabbit Na+-glucose (SGLT1) and the human Na+-Cl−-GABA (GAT1) cotransporters were expressed in Xenopus laevis oocytes, passive Na+ water transport studied using electrical optical techniques. Passive permeabilities (Lp) of determined from changes oocyte volume response to osmotic gradients. The specific SGLT1 GAT1 Lp values obtained by measuring presence absence blockers (phlorizin SKF89976A). In blockers, oocytes expressing indistinguishable control oocytes. (Na+ leak) was blocker-sensitive currents substrates (glucose GABA). 3 Passive through blocked phlorizin with same sensitivity (inhibitory constant (Ki), 3-5 μM). When replaced Li+, also inhibited Li+ transport, but a lower affinity (Ki, 100 choline, which is not transported, that or this case less sensitive phlorizin. 4 The activation energies (Ea) for 21 5 kcal mol−1, respectively. high Ea comparable cotransport indicates process dependent on conformational protein, while low similar channels (aquaporins). 5 GAT1 behaved as an SKF89976A-sensitive channel. We did observe GAT1. 6 We conclude depend different mechanisms: occurs saturable uniport mechanism, permeation conductance SGLT1, we suggest both channel could contribute isotonic fluid across intestinal brush border membrane.