Van Dyke R W, Belcher J D
Department of Medicine, University of California School of Medicine, San Francisco 94143.
Am J Physiol. 1994 Jan;266(1 Pt 1):C81-94. doi: 10.1152/ajpcell.1994.266.1.C81.
Endocytosed ligands move through a series of progressively more acidic vesicles. These differences in pH (pHi) could reflect differences in ion transport mechanisms. Vesicles representing three stages of endocytosis, compartment for uncoupling of receptor and ligand (CURL), multivesicular bodies (MVB), and receptor recycling compartment (RRC), were studied, and all exhibited ATP-dependent electrogenic acidification that was a saturable function of medium chloride. Initial rates of acidification differed (RRC > CURL > MVB), and proton influx was similar for CURL and RRC but slower for MVB. Steady-state ATP-dependent pHi in the three vesicles was more similar. Vesicle membrane potential was substantial (+41 to +69 mV) in low-chloride medium and greatest for RRC but was low (-6 to +6 mV) in 140 mM KCl. These vesicles also exhibited -22 to -37 mV Donnan potentials. Steady-state pump-generated proton electrochemical gradients (delta mu H+) ranged from 114 to 175 mV and were greater for CURL and RRC than for MVB; however, delta mu H+ changed little over a 140-fold difference in chloride concentration. Proton leak rates were faster in CURL and RRC than in MVB, but proton efflux was similar. Finally, proton fluxes and permeabilities, calculated with regard to surface area, differed in the opposite direction (MVB > CURL > RRC). Thus, for the endocytic vesicles studied, intrinsic differences in proton flux and in vesicle geometry could be demonstrated that contributed to differences in pre-steady-state vesicle pHi.
内吞的配体通过一系列酸性逐渐增强的囊泡移动。这些pH值（细胞内pH，pHi）的差异可能反映了离子转运机制的差异。研究了代表内吞作用三个阶段的囊泡，即受体与配体解偶联区室（CURL）、多泡体（MVB）和受体再循环区室（RRC），所有这些囊泡均表现出ATP依赖的生电酸化作用，这是培养基氯化物的饱和函数。酸化的初始速率不同（RRC > CURL > MVB），CURL和RRC的质子内流相似，但MVB的较慢。三个囊泡中ATP依赖的稳态pHi更为相似。在低氯培养基中，囊泡膜电位相当大（+41至+69 mV），RRC的最大，但在140 mM KCl中较低（-6至+6 mV）。这些囊泡还表现出-22至-37 mV的唐南电位。稳态泵产生的质子电化学梯度（δμH+）范围为114至175 mV，CURL和RRC的比MVB的更大；然而，在氯化物浓度相差140倍的情况下，δμH+变化很小。CURL和RRC中的质子泄漏速率比MVB中的更快，但质子外流相似。最后，根据表面积计算的质子通量和渗透率在相反方向上有所不同（MVB > CURL > RRC）。因此，对于所研究的内吞囊泡，可以证明质子通量和囊泡几何形状的内在差异导致了稳态前囊泡pHi的差异。
