Abstract
Activation state of sperm motility named "hyperactivation" enables mammalian sperm to progress through the oviductal matrix, although a similar state of sperm motility is unknown in non-mammalian vertebrates at fertilization. Here, we found a high motility state of the sperm in the newt Cynops pyrrhogaster. It was predominantly caused in egg jelly extract (JE) and characterized by a high wave velocity of the undulating membrane (UM) that was significantly higher at the posterior midpiece. An insemination assay suggested that the high motility state might be needed for sperm to penetrate the egg jelly, which is the accumulated oviductal matrix. Specific characteristics of the high motility state were completely abrogated by a high concentration of verapamil, which blocks the L-type and T-type voltage-dependent Ca(2+) channels (VDCCs). Mibefradil, a dominant blocker of T-type VDCCs, suppressed the wave of the UM at the posterior midpiece with separate wave propagation from both the anterior midpiece and the posterior principal piece. In addition, nitrendipine, a dominant L-type VDCC blocker, weakened the wave of the UM, especially in the anterior midpiece. Live Ca(2+) imaging showed that, compared with the intact sperm in the JE, the relative intracellular Ca(2+) level changed especially in the anterior and posterior ends of the midpiece of the blocker-treated sperm. These suggest that different types of Ca(2+) channels mediate the intracellular Ca(2+) level predominantly in the anterior and posterior ends of the midpiece to maintain the high motility state of the newt sperm.
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