Sayers L G, Michelangeli F
School of Biochemistry, University of Birmingham, Edgbaston, UK.
Biochim Biophys Acta. 1993 Oct 10;1152(1):177-83. doi: 10.1016/0005-2736(93)90245-u.
In this study we show that the potassium-channel blocker tetrahexyl ammonium chloride (THA+) is able to inhibit inositol 1,4,5-trisphosphate (InsP3)-induced calcium release in an apparently biphasic fashion with a IC50 of 3 microM. This inhibition was not alleviated by valinomycin and, therefore, is not consistent with the blocking of K+ counter-ion movement, an observation initially made by Palade et al. (Palade, P., Dettbarn, C., Volpe, P., Alderson, B. and Otero, A.S (1989) Mol. Pharmacol. 36, 664-672). THA+ affected quantal calcium release by reducing the amount of calcium released by InsP3, but did not greatly affect the concentration of InsP3 required to cause half-maximal calcium release. THA+ did not affect the metabolism of InsP3 or its binding to porcine cerebellar microsomes. THA+ could also itself induce calcium release. At concentrations below 100 microM, THA+ appears to release Ca2+ selectively from the InsP3-sensitive calcium stores, since prior depletion of these stores with supramaximal doses of InsP3 abolishes this response. At higher THA+ concentrations (above 100 microM) Ca2+ is released non-selectively from all stores. THA+ has no effect on the Ca(2+)-ATPase activity at concentrations below 100 microM, indicating that selective THA(+)-induced Ca2+ release is not due to non-specific inhibition of the microsomal Ca2+ pumps and does not affect Ca2+ leakage. A number of pharmacological modulators of intracellular calcium channels were also tested on THA(+)-induced calcium release with little effect, except for spermidine which reduced this release by up to 50%. Our observations are consistent with the view that THA+, at concentrations below 100 microM, selectively releases calcium from the InsP3-sensitive calcium stores.
在本研究中，我们发现钾通道阻滞剂氯化四己铵（THA+）能够以明显的双相方式抑制肌醇1,4,5-三磷酸（InsP3）诱导的钙释放，IC50为3 microM。缬氨霉素不能减轻这种抑制作用，因此，这与帕拉德等人最初观察到的K+反离子运动受阻不一致（帕拉德，P.，德特巴恩，C.，沃尔佩，P.，奥尔德森，B.和奥特罗，A.S（1989年）《分子药理学》36卷，664 - 672页）。THA+通过减少InsP3释放的钙量来影响量子钙释放，但对引起半数最大钙释放所需的InsP3浓度影响不大。THA+不影响InsP3的代谢或其与猪小脑微粒体的结合。THA+本身也能诱导钙释放。在浓度低于100 microM时，THA+似乎从InsP3敏感的钙库中选择性地释放Ca2+，因为用超最大剂量的InsP3预先耗尽这些钙库会消除这种反应。在较高的THA+浓度（高于100 microM）下，Ca2+从所有钙库中无选择性地释放。在浓度低于100 microM时，THA+对Ca(2+)-ATP酶活性没有影响，这表明THA(+)选择性诱导的Ca2+释放不是由于微粒体Ca2+泵的非特异性抑制，也不影响Ca2+泄漏。除了亚精胺能将这种释放减少多达50%外，还对多种细胞内钙通道的药理学调节剂对THA(+)诱导的钙释放进行了测试，结果影响不大。我们的观察结果与以下观点一致，即浓度低于100 microM的THA+从InsP3敏感的钙库中选择性地释放钙。
