Loike J D, Cao L, Kuang K, Vera J C, Silverstein S C, Fischbarg J
Department of Physiology and Cellular Biophysics, Columbia University, New York, New York 10032.
J Gen Physiol. 1993 Nov;102(5):897-906. doi: 10.1085/jgp.102.5.897.
We have reported previously that in the presence of an osmotic gradient, facilitative glucose transporters (GLUTs) act as a transmembrane pathway for water flow. Here, we find evidence that they also allow water passage in the absence of an osmotic gradient. We applied the linear diffusion technique to measure the diffusional permeability (Pd) of tritiated water (3H-H2O) through plasma membranes of J774 murine macrophage-like cells. Untreated cells had a Pd of 30.9 +/- 1.8 microns/s; the inhibitors of facilitative glucose transport cytochalasin B (10 microM) and phloretin (20 microM) reduced that value to 15.3 +/- 1.8 (50%) and 11.0 +/- 0.7 (62%) microns/s, respectively. In contrast, no significant effect on Pd was observed in cells treated with dihydrocytochalasin B (Pd = 28.4 +/- 1.5 microns/s). PCMBS (3 mM) inhibited glucose uptake by greater than 95%, and 3H-H2O diffusion by approximately 30% (Pd = 22.9 +/- 1.5 microns/s). The combination of cytochalasin B plus pCMBS reduced Pd by about 87% (Pd = 3.9 +/- 0.3 microns/s). Moreover, 1 mM pCMBS did not affect the osmotic water permeability in Xenopus laevis oocytes expressing the brain/erythroid form of facilitative glucose transporters (GLUT1). These results indicate for the first time that about half of the total Pd of J774 cells may be accounted for by water passage across GLUTs. Hence, they highlight the multifunctional properties of these transporters serving as conduits for both water and glucose. Our results also suggest for the first time that pCMBS blocks glucose transport without affecting water permeation through GLUTs. Lastly, because pCMBS decreases the Pd of J774 cells, this suggests the presence in their plasma membranes of another protein(s) exhibiting water channel properties.
我们之前曾报道，在存在渗透梯度的情况下，易化型葡萄糖转运蛋白（GLUTs）可作为水流动的跨膜通道。在此，我们发现证据表明它们在不存在渗透梯度时也允许水通过。我们应用线性扩散技术来测量氚标记水（3H-H2O）通过J774鼠巨噬细胞样细胞质膜的扩散通透性（Pd）。未处理的细胞Pd为30.9±1.8微米/秒；易化型葡萄糖转运抑制剂细胞松弛素B（10微摩尔）和根皮素（20微摩尔）分别将该值降至15.3±1.8（50%）和11.0±0.7（62%）微米/秒。相比之下，用二氢细胞松弛素B处理的细胞中未观察到对Pd有显著影响（Pd = 28.4±1.5微米/秒）。对氯汞苯甲酸（PCMBS，3毫摩尔）抑制葡萄糖摄取超过95%，并使3H-H2O扩散降低约30%（Pd = 22.9±1.5微米/秒）。细胞松弛素B加pCMBS的组合使Pd降低约87%（Pd = 3.9±0.3微米/秒）。此外，1毫摩尔pCMBS对表达脑/红细胞型易化型葡萄糖转运蛋白（GLUT1）的非洲爪蟾卵母细胞的渗透水通透性没有影响。这些结果首次表明，J774细胞总Pd的约一半可能是由水通过GLUTs所致。因此，它们突出了这些转运蛋白作为水和葡萄糖通道的多功能特性。我们的结果还首次表明，pCMBS阻断葡萄糖转运而不影响水通过GLUTs的渗透。最后，由于pCMBS降低了J774细胞的Pd，这表明在其质膜中存在另一种具有水通道特性的蛋白质。
