Figure 3.

Vanadate-sensitive H⁺ transport changes upon hypo- and hyperosmotic shock. A, PGs were incubated in standard medium (298 mM mannitol), and the pH of the external medium was monitored. Upon sudden osmotic changes (198, 298, and 398 mM mannitol) at t = 0 min, temporal changes in the pH values can be noticed, namely an alkalinization after hypoosmotic shock, no changes after isoosmotic additions, and an increased acidification rate after hyperosmotic challenge. The first 100 s were fitted with a linear regression line giving a pH change rate of 0.0081, 0.0010, and −0.0180 pH units min⁻¹ for 198, 298, and 398 mM mannitol treatments, respectively. B, The low acidification rate before the osmotic challenge was sensitive to vanadate and acidification rates did not change after addition of isoosmolar medium. The alkalinization in the first 100 s after hypoosmotic and the increased acidification rate after hyperosmotic challenge were inhibited by the presence of 500 μM vanadate. Mean values ± SD (n ≥ 3).