Details

Autor(en) / Beteiligte

• Schapiro, Florencia B.
• Grinstein, Sergio

Titel

Determinants of the pH of the Golgi Complex

Ist Teil von

• The Journal of biological chemistry, 2000-07, Vol.275 (28), p.21025-21032

Ort / Verlag

United States: Elsevier Inc

Erscheinungsjahr

2000

Quelle

MEDLINE

Beschreibungen/Notizen

• The factors contributing to the establishment of the steady state Golgi pH (pHG) were studied in intact and permeabilized mammalian cells by fluorescence ratio imaging. Retrograde transport of the nontoxic B subunit of verotoxin 1 was used to deliver pH-sensitive probes to the Golgi complex. To evaluate whether counter-ion permeability limited the activity of the electrogenic V-ATPase, we determined the concentration of K+ in the lumen of the Golgi using a null point titration method. The [K+] inside the Golgi was found to be close to that of the cytosol, and increasing its permeability had no effect on pHG. Moreover, the capacity of the endogenous counter-ion permeability exceeded the rate of H+ pumping, implying that the potential across the Golgi membrane is negligible and has little influence on pHG. The V-ATPase does not reach thermodynamic equilibrium nor does it seem to be allosterically inactivated at the steady state pHG. In fact, active H+ pumping was detectable even below the resting pHG. A steady state pH was attained when the rate of pumping was matched by the passive backflux of H+(equivalents) or “leak.” The nature of this leak pathway was investigated in detail. Neither vesicular traffic nor H+/cation antiporters or symporters were found to contribute to the net loss of H+ from the Golgi. Instead, the leak was sensitive to voltage changes and was inhibited by Zn2+, resembling the H+ conductive pathway of the plasma membrane. We conclude that a balance between an endogenous leak, which includes a conductive component, and the H+pump determines the pH at which the Golgi lumen attains a steady state.