TY - JOUR
T1 - Acidification of three types of liver endocytic vesicles
T2 - Similarities and differences
AU - Van Dyke, R. W.
AU - Belcher, J. D.
PY - 1994
Y1 - 1994
N2 - Endocytosed ligands move through a series of progressively more acidic vesicles. These differences in pH (pH(i)) 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 pH(i) 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 (Δμ̄(H+)) ranged from 114 to 175 mV and were greater for CURL and RRC than for MVB; however, Δμ̄(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 pH(i).
AB - Endocytosed ligands move through a series of progressively more acidic vesicles. These differences in pH (pH(i)) 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 pH(i) 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 (Δμ̄(H+)) ranged from 114 to 175 mV and were greater for CURL and RRC than for MVB; however, Δμ̄(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 pH(i).
KW - compartment for uncoupling of receptor and ligand
KW - endosomes
KW - multivesicular bodies
KW - proton permeability
KW - proton-translocating adenosinetriphosphatase
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U2 - 10.1152/ajpcell.1994.266.1.c81
DO - 10.1152/ajpcell.1994.266.1.c81
M3 - Article
C2 - 8304433
AN - SCOPUS:0028008329
SN - 0002-9513
VL - 266
SP - C81-C94
JO - American Journal of Physiology - Cell Physiology
JF - American Journal of Physiology - Cell Physiology
IS - 1 35-1
ER -