Johnson R G, Carty S, Scarpa A
Fed Proc. 1982 Sep;41(11):2746-54.
A model is presented to explain catecholamine uptake into isolated chromaffin granules and ghosts. It is based on the following observations and conclusions: 1) the chromaffin granule maintains one of the lowest permeabilities to cations of any previously isolated subcellular organelle and the lowest permeability to protons, 2) a transmembrane proton gradient delta pH exists across the chromaffin granule membrane that is not media dependent, with a measured internal pH of 5.5; 3) the addition of ATP to a suspension of chromaffin granules results in the generation of a membrane potential of 80-100 mV, positive inside; 4) an H+-translocating ATPase responsible for the generation of this electrochemical proton gradient (delta micro H+) exists within the membrane of the chromaffin granule; 5) net amine accumulation proceeds in the presence of both a delta pH alone and a transmembrane potential gradient delta psi alone, with the maximal rate and extent occurring in the presence of a delta pH and a delta psi together (delta micro H+); 6) when catecholamine uptake is in equilibrium with the delta micro H+, the equilibrium distribution of amines (delta micro A) obeys the relationship delta micro A = delta psi-2Zdelta pH. The model, in its elemental form, states that an H+-translocating ATPase for the generation of a delta pH and delta psi exists within the membrane of the chromaffin granule. This electrochemical proton gradient provides the driving force for amine influx, which proceeds via a reserpine-sensitive antiport carrier mechanism coupled to proton efflux. The model is discussed in terms of its physiological implications and significance for other amine-containing subcellular organelles, with particular respect to the species of catecholamine transported, and other unresolved issues.
本文提出了一个模型来解释儿茶酚胺摄取到分离的嗜铬颗粒和空泡中的机制。该模型基于以下观察结果和结论：1）嗜铬颗粒对阳离子的通透性是所有先前分离的亚细胞器中最低的之一，对质子的通透性最低；2）跨嗜铬颗粒膜存在一个跨膜质子梯度ΔpH，它不依赖于介质，测得的内部pH为5.5；3）向嗜铬颗粒悬浮液中添加ATP会导致产生80-100 mV的膜电位，内部为正；4）嗜铬颗粒膜内存在一种负责产生这种电化学质子梯度（ΔμH⁺）的H⁺转运ATP酶；5）仅在单独的ΔpH或单独的跨膜电位梯度Δψ存在时，净胺积累就会发生，而在ΔpH和Δψ同时存在（ΔμH⁺）时，积累速率和程度最大；6）当儿茶酚胺摄取与ΔμH⁺达到平衡时，胺的平衡分布（ΔμA）遵循关系ΔμA = Δψ - 2ZΔpH。该模型的基本形式表明，嗜铬颗粒膜内存在一种用于产生ΔpH和Δψ的H⁺转运ATP酶。这种电化学质子梯度为胺的流入提供驱动力，胺的流入通过与质子外流偶联的利血平敏感的反向转运载体机制进行。本文从其生理意义以及对其他含胺亚细胞器的重要性方面对该模型进行了讨论，特别涉及所运输的儿茶酚胺种类以及其他未解决的问题。
