Lidofsky S D, Xie M H, Sostman A, Scharschmidt B F, Fitz J G
Department of Medicine and Liver Center, University of California, San Francisco 94143-0538.
J Biol Chem. 1993 Jul 15;268(20):14632-6.
A variety of hormonal agonists activate transmembrane Na+ and Ca2+ flux in hepatocytes, but the responsible mechanisms are poorly understood. We employed microfluorimetric and patch clamp recording techniques in hepatocytes to determine the effect of the hormone vasopressin on cytosolic Na+ concentration ([Na+]i) and to identify the transmembrane Na+ transport pathways activated by this agonist. Under basal conditions, [Na+]i, measured using the Na(+)-sensitive fluorophore sodium-binding benzofuran isophthalate, averaged 12.1 +/- 1.6 mM. Exposure to vasopressin rapidly increased [Na+]i by 8.3 +/- 0.9 mM. This increase was attributable to activation of Na+ influx. It occurred in the absence of solutes co-transported with Na+ and was not associated with activation of Na+/H+ antiport. In cell-attached membrane patches, vasopressin activated ion channels that carried inward positive current at the resting membrane potential. Further characterization in excised membrane patches revealed two classes of ion channels, with conductances of 16.0 +/- 2.8 and 30.9 +/- 3.1 picosiemens, respectively. Single channel currents reversed near 0 mV, and ion substitution studies demonstrated that each channel type was permeable to Na+, Ca2+, and K+ but not Cl-. These observations in hepatocytes indicate that vasopressin increases [Na+]i and activates cation-selective channels, which likely accounts for vasopressin-activated Na+ and Ca2+ influx.
多种激素激动剂可激活肝细胞中的跨膜钠和钙通量，但相关机制尚不清楚。我们在肝细胞中采用微荧光测定法和膜片钳记录技术，以确定激素血管加压素对细胞溶质钠浓度（[Na⁺]i）的影响，并识别由该激动剂激活的跨膜钠转运途径。在基础条件下，使用钠敏感荧光团钠结合苯并呋喃异邻苯二甲酸酯测量的[Na⁺]i平均为12.1±1.6 mM。暴露于血管加压素会使[Na⁺]i迅速增加8.3±0.9 mM。这种增加归因于钠内流的激活。它发生在没有与钠共转运的溶质的情况下，并且与钠/氢反向转运的激活无关。在细胞贴附膜片中，血管加压素激活了在静息膜电位下携带内向正电流的离子通道。在切除的膜片中进一步表征发现了两类离子通道，电导分别为16.0±2.8和30.9±3.1皮西门子。单通道电流在接近0 mV时反转，离子置换研究表明每种通道类型对钠、钙和钾通透，但对氯不通透。在肝细胞中的这些观察结果表明，血管加压素增加[Na⁺]i并激活阳离子选择性通道，这可能解释了血管加压素激活的钠和钙内流。
