During mammalian fertilization, the contact between sperm and egg triggers increases in intracellular Ca2 concentration ([Ca2 ]i) in sperm. Voltage-gated Ca2 channels (CaVs) are believed to mediate the initial phase of [Ca2 ]i increases in sperm induced by egg coat (zona pellucida [ZP]) glycoproteins, while store depletion-activated Ca2 entry is thought to mediate the sustained phase. Using patch-clamp recording and Ca2 imaging, we show herein that CaV channel currents, while found in spermatogenic cells, are not detectable in epididymal sperm and are not essential for the ZP-induced [Ca2 ]i changes. Instead, CATSPER channels localized in the distal portion of sperm (the principal piece) are required for the ZP-induced [Ca2 ]i increases. Furthermore, the ZP-induced [Ca2 ]i increase starts from the sperm tail and propagates toward the head.
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Vol. 80 • No. 6