Brailoiu Eugen, Dun Nae J
Department of Pharmacology, James H. Quillen College of Medicine, East Tennessee State University, PO Box 70577, Johnson City, TN 37614-1708, USA.
Mol Pharmacol. 2003 Jun;63(6):1430-6. doi: 10.1124/mol.63.6.1430.
Similar to phosphatidylinositol bisphosphate, sphingomyelin breakdown generates several lipids, including sphingosylphosphorylcholine (SPC), that are putative signaling molecules. The present study was undertaken to evaluate the involvement of SPC in transmitter release process. Intracellular recordings were made from isolated frog sciatic-sartorius nerve-muscle preparations, and the effects of SPC on neurosecretion in the form of miniature endplate potentials (MEPPs) were assessed. Extracellular application of SPC mixture (D,L-SPC) at 1, 10, and 25 microM increased the MEPP frequency by 68, 96, and 127%, respectively. D-erythro-SPC (dissolved in dimethyl sulfoxide but not coupled to bovine serum albumin), but not L-threo-SPC, was active extracellular; the former (at 10 microM) increased the MEPP frequency by 143%. D-erythro-SPC treatment did not significantly change the median amplitude or frequency-distribution of MEPPs. Intracellular delivery via liposomes, in which 10, 100, or 1000 microM SPC mixture was entrapped in liposomal aqueous phase, induced a concentration-dependent increase in MEPP frequency of 45, 91, and 100%, respectively. D-erythro-SPC and L-threo-SPC at the concentration of 100 microM increased the MEPP frequency by 117 and 67%, respectively, or 91 and 61%, respectively, when coupled to bovine serum albumin. Pretreatment with thapsigargin significantly reduced but did not abolish the effects of extracellular D-erythro-SPC (10 microM) or liposomes containing 100 microM D-erythro-SPC. Liposomes filled with 100 microM D-myo-inositol 1,4,5-trisphosphate (IP3) enhanced the MEPP frequency to the same magnitude as 100 microM D-erythro-SPC entrapped in liposomes. However, administration of 100 microM D-erythro-SPC and IP3 entrapped in the same liposomes enhanced the MEPP frequency by 70%, which was less than that produced by these two compounds alone. The result provides the first electrophysiological evidence that SPC can modulate transmitter release by an extra- or intracellular action at the frog motor nerve ending.
与磷脂酰肌醇二磷酸类似，鞘磷脂分解会产生几种脂质，包括鞘氨醇磷酸胆碱（SPC），它们都是假定的信号分子。本研究旨在评估SPC在递质释放过程中的作用。从分离的青蛙坐骨 - 缝匠肌神经 - 肌肉标本上进行细胞内记录，并评估SPC对以微小终板电位（MEPPs）形式的神经分泌的影响。在细胞外施加1、10和25微摩尔的SPC混合物（D，L - SPC），分别使MEPP频率增加了68%、96%和127%。D - 赤藓糖型SPC（溶解于二甲基亚砜但未与牛血清白蛋白偶联）在细胞外有活性，而L - 苏阿糖型SPC则无活性；前者（10微摩尔）使MEPP频率增加了143%。D - 赤藓糖型SPC处理并未显著改变MEPPs的中位幅度或频率分布。通过脂质体进行细胞内递送，脂质体水相中包裹有10、100或1000微摩尔的SPC混合物，分别导致MEPP频率浓度依赖性增加45%、91%和100%。浓度为100微摩尔的D - 赤藓糖型SPC和L - 苏阿糖型SPC，与牛血清白蛋白偶联时，分别使MEPP频率增加117%和67%，或分别增加91%和61%。用毒胡萝卜素预处理显著降低但并未消除细胞外D - 赤藓糖型SPC（10微摩尔）或含有100微摩尔D - 赤藓糖型SPC的脂质体的作用。填充有100微摩尔D - 肌醇1,4,5 - 三磷酸（IP3）的脂质体将MEPP频率提高到与包裹有100微摩尔D - 赤藓糖型SPC的脂质体相同的幅度。然而，将100微摩尔D - 赤藓糖型SPC和IP3包裹在同一脂质体中给药，使MEPP频率提高了70%，这低于这两种化合物单独作用时产生的频率增加。该结果提供了首个电生理证据，表明SPC可通过在青蛙运动神经末梢的细胞外或细胞内作用来调节递质释放。
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