Belyaeva E A, Wojtczak L
Nencki Institute of Experimental Biology, Warsaw, Poland.
Biochem Mol Biol Int. 1994 May;33(1):165-75.
K+ homeostasis in mitochondria is maintained by concerted action of the electrophoretic K+ uniport, driven by the membrane potential, and the electroneutral K+/H+ exchange, driven by [K+] and [H+] gradients. Knowing the driving forces of both pathways and the magnitude of net K+ fluxes under various conditions in rat liver mitochondria suspended in isotonic sucrose medium it was possible to evaluate corresponding rate constants. The rate constant for the K+ uniport under energized conditions was calculated as 0.11 nmol x min-1 x mV-1 x mg protein-1 and that of the antiport was about ten times lower. Activation of the exchanger by depletion of mitochondrial Mg2+ with the ionophore A23187 resulted in an almost tenfold increase of its rate constant, approaching that of the uniport. Quinine and Mg2+ inhibited both K+ transport pathways, whereas glibenclamide, blocker of the ATP-sensitive K+ channel, inhibited the uniport only. The uniport was activated by K+ channel opener P1060.
线粒体中的钾离子稳态是由膜电位驱动的钾离子电转运单向转运体和钾离子浓度与氢离子浓度梯度驱动的电中性钾离子/氢离子交换体的协同作用维持的。了解这两条途径的驱动力以及悬浮在等渗蔗糖培养基中的大鼠肝脏线粒体在各种条件下的净钾离子通量大小后，就有可能评估相应的速率常数。在有能量的条件下，钾离子单向转运体的速率常数计算为0.11 nmol×min⁻¹×mV⁻¹×mg蛋白⁻¹，而反向转运体的速率常数约低十倍。用离子载体A23187耗尽线粒体镁离子激活交换体后，其速率常数几乎增加了十倍，接近单向转运体的速率常数。奎宁和镁离子抑制了两条钾离子转运途径，而ATP敏感性钾离子通道阻滞剂格列本脲仅抑制单向转运体。钾离子通道开放剂P1060激活了单向转运体。
