大鼠肝脏线粒体对线粒体外Ca2+的Na+依赖性调节

Na+-dependent regulation of extramitochondrial Ca2+ by rat-liver mitochondria.

作者信息

Nedergaard J

出版信息

Eur J Biochem. 1984 Oct 1;144(1):159-68. doi: 10.1111/j.1432-1033.1984.tb08444.x.

DOI:10.1111/j.1432-1033.1984.tb08444.x

Abstract

The presence and significance of Na+-induced Ca2+ release from rat liver mitochondria was investigated by the arsenazo technique. Under the experimental conditions used, the mitochondria, as expected, avidly extracted Ca2+ from the medium. However, when the uptake pathway was blocked with ruthenium red, only a small rate of 'basal' release of Ca2+ was seen (0.3 nmol Ca2+ X min-1 X mg-1), in marked contrast to earlier reports on a rapid loss of sequestered Ca2+ from rat liver mitochondria. The addition of Na+ in 'cytosolic' levels (20 mM) led to an increase in the release rate by about 1 nmol Ca2+ X min-1 X mg-1. This effect was specific for Na+. The significance of this Na+-induced Ca2+ release, in relation to the Ca2+ uptake mechanism, was investigated (in the absence of uptake inhibitors) by following the change in the extramitochondrial Ca2+ steady-state level (set point) induced by Na+. A five-fold increase in this level, from less than 0.2 microM to more than 1 microM, was induced by less than 20 mM Na+. The presence of K+ increased the sensitivity of the Ca2+ homeostat to Na+. The effect of Na+ on the extramitochondrial level was equally well observed in an K+/organic-anion buffer as in a sucrose buffer. Liver mitochondria incubated under these circumstances actively counteracted a Ca2+ or EGTA challenge by taking up or releasing Ca2+, so that the initial level, as well as the Na+-controlled level, was regained. It was concluded that liver mitochondria should be considered Na+-sensitive, that the capacity of the Na+-induced efflux pathway was of sufficient magnitude to enable it to influence the extramitochondrial Ca2+ level biochemically and probably also physiologically, and that the mitochondria have the potential to act as active, Na+-dependent regulators of extramitochondrial ('cytosolic') Ca2+. It is suggested that changes of cytosolic Na+ could be a mediator between certain hormonal signals (notably alpha 1-adrenergic) and changes in this extramitochondrial ('cytosolic') Ca2+ steady state level.

摘要

采用偶氮胂技术研究了大鼠肝脏线粒体中Na⁺诱导的Ca²⁺释放的存在及其意义。在所采用的实验条件下，正如预期的那样，线粒体从培养基中大量摄取Ca²⁺。然而，当摄取途径被钌红阻断时，仅观察到少量的“基础”Ca²⁺释放速率（0.3 nmol Ca²⁺×min⁻¹×mg⁻¹），这与早期关于大鼠肝脏线粒体中储存的Ca²⁺快速丢失的报道形成了显著对比。添加“胞质”水平（20 mM）的Na⁺导致释放速率增加约1 nmol Ca²⁺×min⁻¹×mg⁻¹。这种效应是Na⁺特有的。通过跟踪由Na⁺诱导的线粒体外Ca²⁺稳态水平（设定点）的变化，研究了这种Na⁺诱导的Ca²⁺释放相对于Ca²⁺摄取机制的意义（在不存在摄取抑制剂的情况下）。小于20 mM的Na⁺可使该水平从小于0.2 μM增加到大于1 μM，增加了五倍。K⁺的存在增加了Ca²⁺稳态对Na⁺的敏感性。在K⁺/有机阴离子缓冲液中与在蔗糖缓冲液中一样，均能很好地观察到Na⁺对线粒体外水平的影响。在这些情况下孵育的肝脏线粒体通过摄取或释放Ca²⁺积极抵抗Ca²⁺或EGTA的挑战，从而恢复初始水平以及Na⁺控制的水平。得出的结论是，肝脏线粒体应被视为对Na⁺敏感，Na⁺诱导的外流途径的能力足以使其在生化上乃至可能在生理上影响线粒体外Ca²⁺水平，并且线粒体有潜力作为线粒体外（“胞质”）Ca²⁺的活性、Na⁺依赖性调节剂发挥作用。有人提出，胞质Na⁺的变化可能是某些激素信号（特别是α1-肾上腺素能信号）与这种线粒体外（“胞质”）Ca²⁺稳态水平变化之间的介质。