Fig. 2. The follicle affords the growing oocyte HCO₃^-/Cl^- activity. (A) pH_i was monitored in denuded (top row) and follicle-enclosed (bottom row) oocytes simultaneously. Cl^- was removed from the bathing medium at 10 minutes in each experiment. Traces shown are the mean of all experiments performed. Note that Cl^- removal causes sharp increases in pH_i in all follicle-enclosed oocytes, but only in larger denuded oocytes. (B) Plot of the rate of pH_i increase, which provides an indication of HCO₃^-/Cl^- activity. HCO₃^-/Cl^- exchange rate increases significantly with increasing oocyte size in denuded oocytes (P<0.0001), whereas there is no difference between sizes in follicle-enclosed oocytes (P>0.8). DIDS inhibited Cl^--induced pH_i increases in follicle-enclosed oocytes (A, bottom row, far right). Each point comprises between four and 17 oocytes from two to eight replicates.