Egg coat proteins activate calcium entry into mouse sperm via CATSPER channels

Abstract

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. © 2009 by the Society for the Study of Reproduction, Inc.