Digital image analysis of flagellar beating and microtubule sliding of activated and hyperactivated sperm flagella

Flagellar beatings of Suncus, golden hamster, and monkey spermatozoa before and after hyperactivation were analysed using high-speed video microscopy and digital image processing in order to examine the sliding mechanism of the flagellar beating and the function of accessory fibres of the mammalian spermatozoa. Although these spermatozoa have different morphology and movement characteristics, the flagellar beatings of hyperactivated spermatozoa had a few common features; i.e., sharp bends at the base of the flagellum and a low beat frequency. While nonhyperactivated (activated) spermatozoa exhibited nearly constant-curvature beating, the hyperactivated spermatozoa displayed a constant-frequency beating. A detailed analysis of the microtubule sliding of the activated and hyperactivated sperm flagella revealed that the sharp bends at the base of the flagella were induced by an increase in the total length of the microtubule sliding at the base of the flagella and that the sliding velocity of the activated and hyperactivated sperm flagella was consistent within each species. A comparison of the sliding velocity of the flagellar beating of Suncus, golden hamster, and monkey spermatozoa with the moment of inertia of the cross section of the flagellar base suggests that the sliding velocity is involved in the hardness of a sperm flagellum.