Fluoride-induced cytoplasmic acidification: possible role of protein kinase C in BCECF-loaded L929 cells

The effect of fluoride on cytoplasmic pH (pHi) in L929 cells was investigated by using a fluorescent pH indicator, BCECF. Fluoride decreased pHi in a dose-dependent manner. This cytoplasmic acidification was composed of two phases: 1) a rapid decrease in pHi occurring within seconds, and 2) a slow decrease in pHi occurring 1-2 min. after stimulation with fluoride. The phase one decrease in pHi at external pH (pHe) 7.7 was more rapid than that at pHe 6.8, whereas the phase two decrease at pHe 7.7 was slower than that at pHe 6.8. In addition, both in the protein kinase C-inhibited and depleted cells, the fluoride-acidified pHi gradually returned to the resting pHi level in phase two, though the initial cytoplasmic acidification (i.e. phase one) was not affected. These results suggest that the fluoride-induced cytoplasmic acidification is dependent upon pHe and is sustained by the protein kinase C-dependent Na+/H+ exchange.