Fig. 6. Changes in [Ca²⁺]i in SWT sperm subjected to hypotonic or hypertonic conditions, indicated by fluo-3 AM. Sperm were incubated with 500 µmol l^-1 fluo-3 AM in artificial seminal plasma (ASP) for 2 h. Approximately 90% of sperm moved after dilution into Ca²⁺-containing hypotonic or hypertonic conditions: (A) 50 mmol l^-1 NaCl + 5 mmol l^-1 CaCl₂ or (D) 300 mmol l^-1 NaCl + 10 mmol l^-1 CaCl₂. Motility was suppressed in Ca²⁺-free hypotonic or hypertonic solutions: (C) 50 mmol l^-1 NaCl + 5 mmol l^-1 EGTA or (B) 300 mmol l^-1 NaCl. Arrows, head and sleeve regions; arrowheads, flagella. (E) In hypertonic conditions the sleeve structure of SWT was expanded but that of FWT was shrunken. Bars, 10 µm. For details of microscopy, see Materials and methods.