Fig. 3. Measurement of [pH]_i using a fluorescent pH indicator, carboxy SNARF-1. (A) The effect of histidine and NH₄Cl on sperm [pH]_i. Carboxy SNARF-1 loaded sperm were suspended in Na-free ASW containing 0 or 10 mmol l^–1 histidine (white bars), ASW containing 0 or 10 mmol l^–1 histidine (gray bars), or choline chloride (CC) solution containing 0 or 20 mmol l^–1 NH₄Cl (black bars). Values are means ± S.D.; N=2. Sperm motility (percentage of motile sperm) in each solution is given under the graph; – and + indicate generally immotile and >60% motile, respectively. (B) Fluorescence micrographs of carboxy SNARF-1 loaded sperm suspended in CC solution containing 0 (left) or 20 mmol l^–1 (right) NH₄Cl. Micrographs represent the fluorescent intensity at 640 nm with 470–550 nm excitation. Bars, 10 µm.