从大鼠神经垂体分离的肽能神经末梢制剂在静息状态下的钙内流。

Calcium influx in resting conditions in a preparation of peptidergic nerve terminals isolated from the rat neurohypophysis.

作者信息

Toescu E C

机构信息

Department of Human Anatomy, Oxford University.

出版信息

J Physiol. 1991 Feb;433:109-25. doi: 10.1113/jphysiol.1991.sp018417.

DOI:10.1113/jphysiol.1991.sp018417

PMID:1668751

原文链接:https://pmc.ncbi.nlm.nih.gov/articles/PMC1181362/

Abstract

Calcium accumulation in a preparation of nerve terminals isolated from the rat neurohypophysis was measured both in rapid (10-60 s) and long-term (up to 60 min) uptake experiments, by use of 45Ca2+ as radiotracer and ion-exchange chromatography as separation method. Unless otherwise stated all experiments have been performed in the absence from the incubation media of secretagogues or depolarizing agents. 2. The uptake of 45Ca2+ in nerve terminals was linear up to 30-45 s, with an apparent initial rate of uptake of 0.98 nmol Ca2+ (mg protein)-1 min-1. 3. The level of 45Ca2+ accumulation was sensitive to manipulations of electrochemical gradient for Na+ across the plasma membrane. Alterations of extracellular concentrations of Na+ affected secretory activity to a larger extent than manipulations of internal Na+. These effects were not qualitatively dependent on the nature of the replacement for Na+. 4. Removal of extracellular Na+ induced a significant increase of both the level of 45Ca2+ accumulation and of the apparent initial rate of uptake. The concentration for half-maximal stimulatory effect was 40 mM-Na+. 5. The analysis of the stimulatory effect of high extracellular K+ on the 45Ca2+ accumulation reveals at least two components: a depolarization and an intrinsic K+ effect. 6. Sodium channel inhibitors (TTX, 1.25 microM) decreased significantly the level of 45Ca2+ accumulation, an effect which was evident from the first minute of exposure to the drug. 7. A specific L-type Ca2+ channel blocker (nicardipine) inhibited 45Ca2+ uptake, in a dose-dependent manner. Simultaneous addition of both TTX and nicardipine (20 microM) decreases the 45Ca2+ uptake up to 50%. 8. In conclusion, the uptake of Ca2+ in isolated peptidergic nerve terminals, incubated in resting conditions, is mediated by at least three pathways: a TTX-sensitive and a nicardipine (dihydropyrine)-sensitive pathway and through a Na(+)-Ca2+ exchange-dependent mechanism. The principal route of Ca2+ entry appears to be through TTX-sensitive channels.

摘要

在从大鼠神经垂体分离的神经末梢制剂中，通过使用⁴⁵Ca²⁺作为放射性示踪剂和离子交换色谱作为分离方法，在快速（10 - 60秒）和长期（长达60分钟）摄取实验中测量钙积累。除非另有说明，所有实验均在无促分泌剂或去极化剂的孵育培养基中进行。2. 神经末梢中⁴⁵Ca²⁺的摄取在30 - 45秒内呈线性，表观初始摄取速率为0.98 nmol Ca²⁺（mg蛋白质）⁻¹分钟⁻¹。3. ⁴⁵Ca²⁺积累水平对跨质膜的Na⁺电化学梯度的操作敏感。细胞外Na⁺浓度的改变对分泌活性的影响比细胞内Na⁺的操作更大。这些效应在质量上不依赖于Na⁺替代物的性质。4. 去除细胞外Na⁺导致⁴⁵Ca²⁺积累水平和表观初始摄取速率均显著增加。半最大刺激效应的浓度为40 mM - Na⁺。5. 对高细胞外K⁺对⁴⁵Ca²⁺积累的刺激作用的分析揭示至少两个成分：去极化和内在K⁺效应。6. 钠通道抑制剂（TTX，1.25 μM）显著降低⁴⁵Ca²⁺积累水平，从接触药物的第一分钟起这种效应就很明显。7. 一种特异性L型Ca²⁺通道阻滞剂（尼卡地平）以剂量依赖性方式抑制⁴⁵Ca²⁺摄取。同时添加TTX和尼卡地平（20 μM）可使⁴⁵Ca²⁺摄取降低多达50%。8. 总之，在静息条件下孵育的分离肽能神经末梢中Ca²⁺的摄取至少由三种途径介导：一种TTX敏感和一种尼卡地平（二氢吡啶）敏感途径以及通过Na⁺ - Ca²⁺交换依赖性机制。Ca²⁺进入的主要途径似乎是通过TTX敏感通道。