Journal
NATURE CELL BIOLOGY
Volume 8, Issue 10, Pages 1149-U198Publisher
NATURE PUBLISHING GROUP
DOI: 10.1038/ncb1473
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Eggs attract sperm by chemical factors, a process called chemotaxis. Sperm from marine invertebrates use cGMP signalling to transduce incident chemoattractants into changes in the Ca2+ concentration in the flagellum, which control the swimming behaviour during chemotaxis(1-3). The signalling pathway downstream of the synthesis of cGMP by a guanylyl cyclase is ill-defined. In particular, the ion channels that are involved in Ca2+ influx and their mechanisms of gating are not known(4). Using rapid voltage-sensitive dyes and kinetic techniques, we record the voltage response that is evoked by the chemoattractant in sperm from the sea urchin Arbacia punctulata. We show that the chemoattractant evokes a brief hyperpolarization followed by a sustained depolarization. The hyperpolarization is caused by the opening of K+-selective cyclic-nucleotide-gated ( CNG) channels in the flagellum. Ca2+ influx commences at the onset of recovery from hyperpolarization. The voltage threshold of Ca2+ entry indicates the involvement of low-voltage-activated Ca-v channels. These results establish a model of chemosensory transduction in sperm whereby a cGMP-induced hyperpolarization opens Ca-v channels by a 'recovery-from-inactivation' mechanism and unveil an evolutionary kinship between transduction mechanisms in sperm and photoreceptors.
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