Translational suppression by Ca2+ ionophores: Reversibility and roles of Ca2+ mobilization, Ca2+ influx, and nucleotide depletion
Translational suppression by Ca2+ ionophores: Reversibility and roles of Ca2+ mobilization, Ca2+ influx, and nucleotide depletion
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DOI：
10.1007/bf00143360
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发表时间：
1996-04-01
影响因子：
6.1
通讯作者：
Brostrom, MA
中科院分区：
文献类型：
--
作者：
Gmitter, D;Brostrom, CO;Brostrom, MA
比较了二价阳离子选择载体A23187和离子霉素对几种培养细胞的钙离子含量、核苷酸含量和蛋白质合成速率的影响。在低浓度(50-300nmol/L)时，两种离子载体均可使培养的哺乳动物细胞的氨基酸掺入减少约85%，而不降低三磷酸腺苷或谷氨酸的含量。在这些浓度下，A23187和离子霉素都促进了大量的Ca~(2+)外流，而在较高浓度下，观察到大量的阳离子内流。C6胶质瘤和P3X63Ag8骨髓瘤较GH(3)细胞有较低的离子载体浓度和较大的钙离子内流。细胞的ATP和GTP含量及其贴壁生长表面的能力在离子载体浓度下急剧下降，产生更多的钙离子内流。在含有EGTA的培养液中，核苷酸含量显著减少，而细胞外钙离子进一步加剧了这一现象。与可比浓度的A23187相比，离子霉素产生更多的钙离子内流和核苷酸下降。不含脂肪酸的牛血清白蛋白可逆转离子霉素对GH(3)细胞内氨基酸掺入的抑制和细胞内钙离子的动员，而A23187的作用仅被部分逆转。氨基酸掺入被耗尽核苷酸含量的离子载体浓度进一步抑制。线粒体解偶联剂增强了钙离子的积累，以响应两个离子载体。在细胞毒性浓度下，Lubrol PX抑制蛋白质合成，但不引起钙内流。在高离子载体浓度下核苷酸的耗尽被认为是由于质膜Ca~(2+)-ATPase活性的增加和线粒体质子梯度的耗散以及引起细胞内的Ca~(2+)积累所致。钙离子载体引起的细胞内钙离子含量的增加被认为是离子载体诱导的细胞毒性的指标。
The divalent cation selective ionophores A23187 and ionomycin were compared for their effects on the Ca2+ contents, nucleotide contents, and protein synthetic rates of several types of cultured cells. Both ionophores reduced amino acid incorporation by approximately 85% at low concentrations (50-300 nmol/L) in cultured mammalian cells without reducing ATP or GTP contents. At these concentrations A23187 and ionomycin each promoted substantial Ca2+ efflux, whereas at higher concentrations a large influx of the cation was observed. Ca2+ influx occurred at lower ionophore concentrations and to greater extents in C6 glioma and P3X63Ag8 myeloma than in GH(3) pituitary cells. The ATP and GTP contents of the cells and their ability to adhere to growth surfaces declined sharply at ionophore concentrations producing increased Ca2+ influx. Prominent reductions of nucleotide contents occurred in EGTA-containing media that were further accentuated by extracellular Ca2+. Ionomycin produced more Ca2+ influx and nucleotide decline than comparable concentrations of A23187. The inhibition of amino acid incorporation and mobilization of cell-associated Ca2+ by ionomycin were readily reversed in GH(3) cells by fatty acid-free bovine serum albumin, whereas the effects of A23187 were only partially reversed. Amino acid incorporation was further suppressed by ionophore concentrations depleting nucleotide contents. Mitochondrial uncouplers potentiated Ca2+ accumulation in response to both ionophores. At cytotoxic concentrations Lubrol PX abolished protein synthesis but did not cause Ca2+ influx. Nucleotide depletion at high ionophore concentrations is proposed to result from increased plasmalemmal Ca2+-ATPase activity and dissipation of mitochondrial proton gradients and to cause intracellular Ca2+ accumulation. Increased Ca2+ contents in response to Ca2+ ionophores are proposed as an indicator of ionophore-induced cytotoxicity.