Takebayashi M, Kagaya A, Uchitomi Y, Yokota N, Horiguchi J, Yamawaki S
Department of Psychiatry and Neurosciences, Hiroshima University School of Medicine, Japan.
Neurochem Int. 1998 Feb;32(2):205-11. doi: 10.1016/s0197-0186(97)00070-3.
We investigated the effects of pregnenolone sulfate (PS) on the [Ca2+]i increase induced by gamma-aminobutyric acid (GABA) and N-methyl-D-aspartate (NMDA) using fluorescence imaging. PS inhibited the 50 microM GABA-induced increase in [Ca2+]i in a dose-dependent manner with an IC50 of 30 microM. The inhibitory effect of PS was apparent within 5 min and was in a non-competitive manner, suggesting that PS may act directly to the membrane level but indirectly to the GABA binding sites. Our previous study has already shown that the GABA-induced Ca2+ increase involves GABAA receptors and the similar pathway to a high K(+)-induced Ca2+ response (Takebayashi et al., 1996). Because 50 microM of PS could not inhibit a 25 mM K(+)-induced Ca2+ increase, it seems likely that the site of the inhibitory action of PS on the GABA-induced Ca2+ increase may be independent of the pathway of the high K(+)-induced Ca2+ response, but rather at GABAA receptor complex. In contrast, PS potentiated the 50 microM NMDA-induced increase in [Ca2+]i in a dose-dependent manner. The magnitude of the NMDA response was approximately doubled in the presence of 100 microM of PS. However, PS did not affect the acetylcholine(Ach)-induced increase in [Ca2+]i. Furthermore, corticosterone had little effect on the GABA- and NMDA-induced Ca2+ increases, indicating that the alteration of the Ca2+ response is specific for PS. In conclusion, it is suggested that PS modulates differentially [Ca2+]i increase induced by GABA and NMDA.
我们使用荧光成像技术研究了硫酸孕烯醇酮（PS）对γ-氨基丁酸（GABA）和N-甲基-D-天冬氨酸（NMDA）诱导的细胞内钙离子浓度（[Ca2+]i）升高的影响。PS以剂量依赖的方式抑制50微摩尔GABA诱导的[Ca2+]i升高，半数抑制浓度（IC50）为30微摩尔。PS的抑制作用在5分钟内即明显显现，且呈非竞争性，提示PS可能直接作用于膜水平，但间接作用于GABA结合位点。我们之前的研究已经表明，GABA诱导的钙离子升高涉及GABAA受体以及与高钾（K+）诱导的钙离子反应相似的途径（Takebayashi等人，1996年）。由于50微摩尔的PS不能抑制25毫摩尔K+诱导的钙离子升高，PS对GABA诱导的钙离子升高的抑制作用位点似乎独立于高K+诱导的钙离子反应途径，而可能位于GABAA受体复合物处。相比之下，PS以剂量依赖的方式增强了50微摩尔NMDA诱导的[Ca2+]i升高。在存在100微摩尔PS的情况下，NMDA反应的幅度大约增加了一倍。然而，PS不影响乙酰胆碱（Ach）诱导的[Ca2+]i升高。此外，皮质酮对GABA和NMDA诱导的钙离子升高几乎没有影响，表明钙离子反应的改变是PS特有的。总之，提示PS对GABA和NMDA诱导的[Ca2+]i升高有不同的调节作用。
