Calcium in the flagellum controls sperm navigation. In sperm of marine invertebrates and mammals, Ca2(+) signalling has been intensely studied, whereas for fish little is known. In sea urchin sperm, a cyclic nucleotide-gated K(+) channel (CNGK) mediates a cGMP-induced hyperpolarization that evokes Ca2(+) influx. Here, we identify in sperm of the freshwater fish Danio rerio a novel CNGK family member featuring non-canonical properties. It is located in the sperm head rather than the flagellum and is controlled by intracellular pH, but not cyclic nucleotides. Alkalization hyperpolarizes sperm and produces Ca2(+) entry. Ca2(+) induces spinning-like swimming, different from swimming of sperm from other species. The 'spinning' mode probably guides sperm into the micropyle, a narrow entrance on the surface of fish eggs. A picture is emerging of sperm channel orthologues that employ different activation mechanisms and serve different functions. The channel inventories probably reflect adaptations to species-specific challenges during fertilization.
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SchlagwörterBiophysics ; Cell Biology ; Structural Biology ; Zebrafish; Sea-urchin Sperm; Nucleotide-binding Domain; Loti K1 Channel; Human Spermatozoa; Catsper Channel; Ion Channels; Controls Chemosensation; Motility Initiation; Rod Photoreceptors; Cyclic-nucleotides