Iouzalen L, David-Dufilho M, Devynck M A
Department of Pharmacology, Centre National de la Recherche Scientifique, Université Paris V, Necker's Medical School, France.
Biochem Pharmacol. 1995 Mar 30;49(7):893-9. doi: 10.1016/0006-2952(94)00513-l.
To further analyse the role of the refilling state of internal Ca2+ pools in the stimulation of Ca2+ influx in human endothelial cells, we investigated the combined effect of thapsigargin (TG) and histamine on cytosolic Ca2+ concentration ([Ca2+]i) and inositol polyphosphate production. At normal extracellular Ca2+ levels, TG induced a progressive and sustained elevation in [Ca2+]i which was dose-dependently prevented by pretreatment with 1-10 microM histamine. Similarly, pretreatment with 0.1 and 1 microM TG suppressed histamine-induced Ca2+ transients partially and totally, respectively. TG pretreatment did not alter the inositol triphosphate (IP3) level liberated by histamine, but modified IP3 metabolism by decreasing inositol biphosphate (IP2) and increasing inositol monophosphate (IP1) contents. In the absence of Ca2+ influx, 1 microM TG only induced a small transient increase in [Ca2+]i whereas the Ca2+ mobilization evoked by 10 microM histamine was unchanged. In both cases, the absence of any additional effect of either TG, histamine or 2 microM ionomycin indicated the complete depletion of Ca2+ stores. The re-establishment of the transmembrane Ca2+ gradient induced a transient rise in [Ca2+]i. Its amplitude differed between histamine- and TG-treated cells. It was imposed by cell pretreatment and was selectively affected by changes in the membrane potential. At 5 mM external K+, the transient rise in [Ca2+]i was more marked in histamine- than in TG-stimulated cells; this difference was suppressed by TG pretreatment. The presence of 130 mM external K+ increased Ca2+ entry in TG-treated cells but reduced it in histamine-stimulated cells. These results indicate that the refilling state of internal Ca2+ stores does not constitute the single regulator of Ca2+ influx. TG and histamine seem to activate Ca2+ influx through distinct but interdependent pathways regulated by membrane potential.
为了进一步分析细胞内钙离子池的再填充状态在刺激人内皮细胞钙离子内流中的作用，我们研究了毒胡萝卜素（TG）和组胺对细胞质钙离子浓度（[Ca2+]i）以及肌醇多磷酸生成的联合影响。在正常细胞外钙离子水平下，TG诱导[Ca2+]i进行性且持续升高，而1 - 10微摩尔组胺预处理可剂量依赖性地阻止这种升高。同样，0.1微摩尔和1微摩尔TG预处理分别部分和完全抑制了组胺诱导的钙离子瞬变。TG预处理并未改变组胺释放的肌醇三磷酸（IP3）水平，但通过降低肌醇二磷酸（IP2）并增加肌醇单磷酸（IP1）含量来改变IP3代谢。在无钙离子内流的情况下，1微摩尔TG仅诱导[Ca2+]i出现小的瞬态升高，而10微摩尔组胺引起的钙离子动员未改变。在这两种情况下，TG、组胺或2微摩尔离子霉素均无任何额外效应，表明钙离子储存完全耗尽。跨膜钙离子梯度的重建诱导了[Ca2+]i的瞬态升高。其幅度在组胺处理细胞和TG处理细胞之间有所不同。它由细胞预处理引起，并受到膜电位变化的选择性影响。在外部钾离子浓度为5毫摩尔时，[Ca2+]i的瞬态升高在组胺刺激的细胞中比在TG刺激的细胞中更明显；这种差异被TG预处理所抑制。外部钾离子浓度为130毫摩尔时，增加了TG处理细胞中的钙离子内流，但降低了组胺刺激细胞中的钙离子内流。这些结果表明，细胞内钙离子储存的再填充状态并非钙离子内流的唯一调节因子。TG和组胺似乎通过由膜电位调节的不同但相互依赖的途径激活钙离子内流。
