Graier W F, Schmidt K, Kukovetz W R
Institut für Pharmakodynamik und Toxikologie, Universitätsplatz 2, Graz, Austria.
Cell Signal. 1990;2(4):369-75. doi: 10.1016/0898-6568(90)90067-k.
Sodium fluoride was used to investigate a possible involvement of G-proteins in the regulation of endothelial calcium channels. Incubation of cultured porcine aortic endothelial cells with sodium fluoride produced a dose-dependent increase in intracellular free calcium (EC50 approximately 5 mM). The effect strictly depended on the presence of extracellular CaCl2, indicating an enhanced influx of extracellular Ca2+ rather than a release of Ca2+ from intracellular stores. The Al3+ chelator deferoxamine abolished the stimulatory effect of sodium fluoride but did not interfere with the stimulatory effect of bradykinin. These data confirm the current hypothesis that the complex AlF-4 and not the fluoride anion activates G-proteins and exclude a direct inhibitory effect of deferoxamine on Ca2(+)-uptake. In contrast to isoproterenol and 5'-N-ethylcarboxamido-adenosine (NECA), which elevated endothelial cAMP-levels without affecting intracellular Ca2(+)-concentrations, sodium fluoride was not able to increase endothelial cAMP. This indicates that the effect of sodium fluoride on endothelial Ca2(+)-levels is not due to stimulation of a Gs-protein. Similar to its effect on cytoplasmic Ca2+, sodium fluoride also increased endothelial cGMP-levels which has recently been suggested to serve as biochemical marker for the formation of endothelium derived relaxing factor (EDRF). Thus, similar to the activation of receptor operated calcium channels, direct stimulation of a G-protein by sodium fluoride results in an increase of cytoplasmic Ca2+ and the formation of EDRF.
用氟化钠研究G蛋白在调节内皮细胞钙通道中可能的作用。用氟化钠孵育培养的猪主动脉内皮细胞，可使细胞内游离钙呈剂量依赖性增加（半数有效浓度约为5 mM）。该效应严格依赖于细胞外氯化钙的存在，表明细胞外Ca2+内流增加，而非细胞内钙库释放Ca2+。铝离子螯合剂去铁胺消除了氟化钠的刺激作用，但不干扰缓激肽的刺激作用。这些数据证实了当前的假说，即AlF-4复合物而非氟阴离子激活G蛋白，并排除了去铁胺对Ca2+摄取的直接抑制作用。与异丙肾上腺素和5'-N-乙基羧酰胺腺苷（NECA）不同，它们可提高内皮细胞cAMP水平而不影响细胞内Ca2+浓度，氟化钠不能增加内皮细胞cAMP。这表明氟化钠对内皮细胞Ca2+水平的影响并非由于刺激Gs蛋白。与对细胞质Ca2+的作用类似，氟化钠也增加了内皮细胞cGMP水平，最近有人提出cGMP水平可作为内皮衍生舒张因子（EDRF）形成的生化标志物。因此，与受体操纵性钙通道的激活类似，氟化钠直接刺激G蛋白会导致细胞质Ca2+增加和EDRF形成。
