Fig. 6. Effects of 100 µmol l^–1 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) (A), control treatment with neither DIDS nor solubilised apical plasma membrane protein fraction (sAPM) (B) and 50 µg ml^–1 sAPM (C) on the intracellular pH of boar spermatozoa incubated for 1 h in the presence (filled circles) and absence (open squares) of bicarbonate/CO₂. Whereas bicarbonate/CO₂ induced increased pH_i in all treatments, DIDS significantly inhibited (F_1,252=93.3; P<0.001) and sAPM significantly enhanced (F_1,356=52.45; P<0.001) the pH increase with respect to the control. (Data are means ± s.e.m.; N=6