Nikmo A, Björklund S, Vainio M, Ekokoski E, Törnquist K
Department of Biology, Abo Akademi University, BioCity, Turku, Finland.
Biochem Biophys Res Commun. 1999 May 19;258(3):812-5. doi: 10.1006/bbrc.1999.0702.
In the present investigation of rat thyroid FRTL-5 cells, we show using reverse-transcriptase PCR that these cells express both Edg-1 and Edg-5. We show using a [35S]GTPgammaS-binding assay that sphingosylphosphorylcholine (SPC), which binds to both Edg-1 and EDG-5, activates Gq, Gi-2, and Gi-3 proteins. SPC potently increases intracellular free calcium concentrations ([Ca2+]i). This effect is mediated through both Gq and Gi proteins, as the mobilization of sequestered calcium was insensitive to pertussis toxin (i.e., mediated by Gq), while the SPC-evoked calcium entry was inhibited by pretreatment with pertussis toxin (i.e., mediated by Gi). Furthermore, SPC in a concentration-dependent manner increases intracellular pH in acidified cells via a Na+-H+ exchange mechanism. The enhanced activation of Na+-H+ exchange is independent of both an increase in [Ca2+]i and an activation of protein kinase C. The effect of SPC on Na+-H+ exchange is insensitive to pertussis toxin, suggesting an effect mediated via Gq.
在目前对大鼠甲状腺FRTL-5细胞的研究中，我们通过逆转录聚合酶链反应表明，这些细胞同时表达Edg-1和Edg-5。我们通过[35S]GTPγS结合试验表明，与Edg-1和EDG-5都结合的鞘氨醇磷酸胆碱（SPC）可激活Gq、Gi-2和Gi-3蛋白。SPC能显著提高细胞内游离钙浓度（[Ca2+]i）。这种效应是通过Gq和Gi蛋白介导的，因为储存钙的动员对百日咳毒素不敏感（即由Gq介导），而SPC诱发的钙内流则被百日咳毒素预处理所抑制（即由Gi介导）。此外，SPC通过Na+-H+交换机制以浓度依赖的方式增加酸化细胞内的pH值。Na+-H+交换的增强激活与[Ca2+]i的增加和蛋白激酶C的激活均无关。SPC对Na+-H+交换的作用对百日咳毒素不敏感，提示其作用是通过Gq介导的。
