Hyperactivated Motility is Induced by Reagents Depressing the Function of Calcium in Mouse Sperm

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To investigate the role of Ca²⁺ on the regulatory mechanism of hyperactivation, mouse sperm were treated with a calcium ionophore, ionomycin and a calmodulin inhibitor, W-13, and were analyzed for swimming pattern and flagellar bending. On the successive frames of photographs, the linearity of swimming and the bend angle were measured. Both reagents induced a non-linear swimming pattern as is observed in spontaneously hyperactivated sperm. However, changes in flagellar bending occurred in a different manner. After the occurrence of hyperactivation, the bend angle in the midpiece region was increased to the same direction as the curve of hook-shaped heads. Treatment with W-13 or ionomycin plus EGTA also increased the bend angle to that direction, whereas ionomycin plus Ca²⁺ increased it to opposite direction. The analysis for asymmetry of flagellar bending also revealed that the treatment with W-13 increased asymmetry to the same direction as the curve of head as is observed in spontaneously hyperactivated sperm and that ionomycin plus Ca²⁺ increased it to opposite direction. These results suggest that the depression of function of machinery controlled by Ca²⁺ is involved in the mechanism by which the sperm begin hyperactivated motility.