Wang K N, Wondergem R
Department of Physiology, James H. Quillen College of Medicine, East Tennessee State University, Johnson City 37614.
Biochim Biophys Acta. 1991 Nov 4;1069(2):187-96. doi: 10.1016/0005-2736(91)90123-p.
Hepatocyte transmembrane potential (Vm) behaves as an osmometer and varies with changes in extracellular osmotic pressure created by altering the NaCl concentration in the external medium (Howard, L.D. and Wondergem, R. (1987) J. Membr. Biol. 100, 53). We now have demonstrated similar effects on Vm by increasing external osmolality with added sucrose and not altering ionic strength. We also have demonstrated that hyperosmotic stress-induced depolarization of Vm results from changes in membrane K+ conductance, gK, rather than from changes in the K+ equilibrium potential. Vm and aKi of hepatocytes in liver slices were measured by conventional and ion-sensitive microelectrodes, respectively. Cell water vols. were estimated by differences in wet and dry weights of liver slices after 10-min incubations. Effect of hyperosmotic medium on membrane transference number for K+, tK, was measured by effects on Vm of step-changes in external [K+]. Hepatocyte Vm decreased 34, 52 and 54% when tissue was superfused with medium made hyperosmotic with added sucrose (50, 100 and 150 mM). Correspondingly, aKi increased 10, 18 and 29% with this hyperosmotic stress of added sucrose. Tissue water of 2.92 +/- 0.10 kg H2O/kg dry weight in control solution decreased to 2.60 +/- 0.05, 2.25 +/- 0.06 and 2.22 +/- 0.05 kg H2O/kg dry weight with additions to medium of 50, 100 and 150 mM sucrose, respectively. Adding 50 mM sucrose to medium decreased tK from 0.20 +/- 0.01 to 0.05 +/- 0.01. Depolarization by 50% with hyperosmotic stress (100 mM sucrose) also occurred in Cl-free medium where Cl- was substituted with gluconate. We conclude that hepatocytes shrink during hyperosmotic stress, and the aKi increases. The accompanying decrease in Vm is opposite to that expected by an increase in aKi, and at least in part results from a concomitant decrease in gK. Changes in membrane Cl- conductance most likely do not contribute to osmotic stress-induced depolarization, since equivalent decreases in Vm occurred with added sucrose in cells depleted of Cl- by superfusing tissue with Cl-free medium.
肝细胞跨膜电位（Vm）起着渗透计的作用，并随通过改变外部介质中NaCl浓度所产生的细胞外渗透压变化而变化（霍华德，L.D.和旺德根姆，R.（1987年）《膜生物学杂志》100卷，53页）。我们现在已经证明，通过添加蔗糖增加外部渗透压而不改变离子强度，对Vm有类似的影响。我们还证明，高渗应激诱导的Vm去极化是由膜K+电导（gK）的变化引起的，而不是由K+平衡电位的变化引起的。肝切片中肝细胞的Vm和aKi分别通过传统微电极和离子敏感微电极进行测量。细胞水体积通过孵育10分钟后肝切片湿重和干重的差异来估计。通过外部[K+]的阶跃变化对Vm的影响来测量高渗介质对K+膜迁移数（tK）的影响。当用添加蔗糖（50、100和150 mM）制成的高渗介质灌注组织时，肝细胞Vm分别降低了34%、52%和54%。相应地，随着添加蔗糖的这种高渗应激，aKi分别增加了10%、18%和29%。对照溶液中2.92±0.10 kg H2O/kg干重的组织水，在分别添加50、100和150 mM蔗糖到介质中后，分别降至2.60±0.05、2.25±0.06和2.22±0.05 kg H2O/kg干重。向介质中添加50 mM蔗糖使tK从0.20±0.01降至0.05±0.01。在无Cl-的介质中，用葡萄糖酸盐替代Cl-时，高渗应激（100 mM蔗糖）也会导致50%的去极化。我们得出结论，在高渗应激期间肝细胞会收缩，且aKi增加。伴随的Vm降低与aKi增加所预期的情况相反，并且至少部分是由gK的同时降低导致的。膜Cl-电导的变化很可能对渗透应激诱导的去极化没有贡献，因为在用无Cl-介质灌注组织使细胞中Cl-耗尽的情况下，添加蔗糖时Vm也会出现同等程度的降低。
