Fig. 4. Motility-dependent dephosphorylation at serine residues in hypotonic conditions. Sperm were diluted in either 300 mmoll^-1 NaCl solution (lane A), 50 mmoll^-1 NaCl + 5 mmoll^-1 CaCl₂ (lane B), or 50 mmoll^-1 NaCl + 5 mmoll^-1 EGTA (lane C). Sperm were motile in the hypotonic solutions (containing 50 mmoll^-1 NaCl; B,C) and immotile in the hypertonic solution (300 mmoll^-1 NaCl; A). Sperm were collected and subjected to western blotting with anti-phosphoserine antibody. Numbers on the left indicate molecular mass markers. Motility is shown below the lanes.