Kass G E, Chow S C, Gahm A, Webb D L, Berggren P O, Llopis J, Orrenius S
Institute of Environmental Medicine, Division of Toxicology, Karolinska Institutet, Stockholm, Sweden.
Biochim Biophys Acta. 1994 Sep 8;1223(2):226-33. doi: 10.1016/0167-4889(94)90230-5.
The plasma membrane Ca2+ carrier system involved in receptor-mediated Ca2+ entry was studied. Using the Ca2+ readdition protocol, the rate of cytosolic free Ca2+ concentration ([Ca2+]i) increase in vasopressin-pretreated hepatocytes was significantly higher than in thapsigargin- or 2,5-di(tert-butyl)hydroquinone-pretreated cells. The addition of Mn2+ to unstimulated hepatocytes resulted in a biphasic quench of fura-2 fluorescence. After an initial phase that was fast in rate but of short duration, the rate of fura-2 quench by Mn2+ became much slower and lasted until all the cellular fura-2 was quenched. Pretreatment of the cells with vasopressin only accelerated the rate of the latter phase but not of the initial one. In agonist-stimulated cells, acidification of the extracellular medium or the presence of ruthenium red, econazole or SK&F 96365 decreased the rates of both [Ca2+]i increase and Mn2+ entry upon addition of the respective cation. By contrast, neomycin and N-tosyl-L-phenylalanine chloromethyl ketone markedly decreased the rate of [Ca2+]i increase upon Ca2+ readdition but had no effect on vasopressin-stimulated Mn2+ entry. None of the treatments affected the ability of vasopressin and thapsigargin to mobilize the internal Ca2+ store. It is concluded that in hepatocytes the two pathways of receptor-mediated Ca2+ entry control two distinct yet pharmacologically related cation carriers.
对参与受体介导的钙离子内流的质膜钙离子载体系统进行了研究。采用钙离子再添加方案，血管加压素预处理的肝细胞中胞质游离钙离子浓度（[Ca2+]i）增加的速率显著高于毒胡萝卜素或2,5 - 二（叔丁基）对苯二酚预处理的细胞。向未受刺激的肝细胞中添加锰离子会导致fura - 2荧光的双相淬灭。在速率快但持续时间短的初始阶段之后，锰离子对fura - 2的淬灭速率变得慢得多，并持续到所有细胞内的fura - 2都被淬灭。仅用血管加压素预处理细胞只会加速后一阶段的速率，而不会加速初始阶段的速率。在激动剂刺激的细胞中，细胞外培养基酸化或存在钌红、益康唑或SK&F 96365会降低添加相应阳离子后[Ca2+]i增加的速率和锰离子内流的速率。相比之下，新霉素和N - 甲苯磺酰 - L - 苯丙氨酸氯甲基酮在钙离子再添加时显著降低[Ca2+]i增加的速率，但对血管加压素刺激的锰离子内流没有影响。这些处理均不影响血管加压素和毒胡萝卜素动员细胞内钙离子储存的能力。结论是，在肝细胞中，受体介导的钙离子内流的两条途径控制着两个不同但在药理学上相关的阳离子载体。
