Movement of Vesicles in Eucariotic Cells. Role of Intravesicle Protons as a Fuel and Modulation of Their Concentration by Drugs or Metabolic Changes.

Import (endocytosis) and export (secretion) of molecules from the cells is mediated by vesicles (lysosomes, endosomes) sliding along microtubules or actin filaments. These vesicles share a common feature: an internal pH of about 5, with an inner protons concentration 1000 fold higher than in the surrounding cytoplasm. As the proton gradient in mitochondria is able to drive ATP synthesis we can expect a similar role (energy supplier) for protons in all acidic vesicles. To experimentally test the vesicles' transport we have loaded them with a fluorescent dye (chloroquine) and then measured its efflux over 5 hours. This efflux was reduced by all treatments lowering the actual concentration of protons in the vesicles, independently of the properties. Treatments included lowering intracellular NADH, inhibitors of ATP-dependent proton translocase and/or the Na + /H + antiport, drugs that accumulate into lysosomes, buffering its acidity (chloroquine, doxorubicin). These results support the idea of a role of a proton gradient as a fuel for protein motors.