Lutz T A, Wild S, Boutellier S, Sutter D, Volkert M, Scharrer E
Institute of Veterinary Physiology, University of Zurich, Winterthurerstrasse 260, 8057 Zurich, Switzerland.
Biochim Biophys Acta. 1998 Jul 17;1372(2):359-69. doi: 10.1016/s0005-2736(98)00078-9.
Using superfused mouse liver slices combined with a conventional microelectrode technique, we investigated: (1) the ionic mechanisms involved in the hyperpolarization of the hepatocyte membrane induced by lactate and other gluconeogenic substrates; (2) whether these mechanisms are similar to those underlying the hyperpolarization induced by cell swelling in hypo-osmotic medium; and (3) whether the hyperpolarizing effect of lactate on the hepatocyte membrane is related to gluconeogenesis. Lactate (5 mmol/l) hyperpolarized the hepatocyte membrane after an exposure of 10-20 min, and the hyperpolarization was still present after 70 min. The hyperpolarization induced by lactate, pyruvate (5 mmol/l) and fructose (10 mmol/l), and by exposure to hypo-osmotic medium (250 mosmol/l) was antagonized by ouabain, tetraethylammonium (TEA), and cetiedil (lactate; hypo-osmotic medium). Hyperpolarization induced by lactate was eliminated or attenuated by agents impairing activation of Ca2+-dependent K+ channels, by amiloride, and by a blockade of non-selective cation channels with flufenamic acid and gadolinium. Thapsigargin, increasing cytosolic Ca2+, mimicked lactate's hyperpolarizing effect. Lactate's effect was dependent on extracellular Ca2+. Finally, lactate's hyperpolarizing effect was reduced by inhibiting gluconeogenesis. These findings suggest that metabolism of lactate hyperpolarizes hepatocytes by mechanisms analogous to those underlying the hyperpolarization induced by cell swelling in hypo-osmotic medium. Gluconeogenesis from lactate may cause cell swelling, subsequent activation of Ca2+-dependent K+ channels and of the Na+/K+-ATPase, and thus hyperpolarize the hepatocyte membrane.
我们使用灌注的小鼠肝脏切片结合传统微电极技术，研究了：（1）乳酸和其他糖异生底物诱导肝细胞膜超极化所涉及的离子机制；（2）这些机制是否与低渗介质中细胞肿胀诱导的超极化机制相似；（3）乳酸对肝细胞膜的超极化作用是否与糖异生有关。乳酸（5 mmol/l）在暴露10 - 20分钟后使肝细胞膜超极化，70分钟后超极化仍存在。乳酸、丙酮酸（5 mmol/l）和果糖（10 mmol/l）以及暴露于低渗介质（250 mosmol/l）诱导的超极化被哇巴因、四乙铵（TEA）和西替地尔（乳酸；低渗介质）所拮抗。乳酸诱导的超极化被损害钙依赖性钾通道激活的试剂、阿米洛利以及用氟芬那酸和钆阻断非选择性阳离子通道所消除或减弱。毒胡萝卜素增加胞质钙，模拟了乳酸的超极化作用。乳酸的作用依赖于细胞外钙。最后，通过抑制糖异生降低了乳酸的超极化作用。这些发现表明，乳酸的代谢通过类似于低渗介质中细胞肿胀诱导的超极化机制使肝细胞超极化。乳酸的糖异生可能导致细胞肿胀，随后激活钙依赖性钾通道和钠/钾 - ATP酶，从而使肝细胞膜超极化。
