Ci-VSP's voltage sensor (blue) regulates a phosphatase domain (green), not a pore domain (pink), as in voltage-gated channels.
OKAMURA/MACMILLAN
Using an in vivo bioassay, Okamura's group showed that Ci-VSP changes cellular phosphoinositide concentrations in response to membrane potential changes. “These data provide the first evidence since the Hodgkin-Huxley age that a molecular function other than that of ion channels is regulated by membrane voltage,” he says.
Ci-VSP is expressed in sperm and might function in sperm motility or morphology. The authors' next goal is to identify the natural substrate of Ci-VSP, which they suspect is PIP3, so that they can determine whether membrane hyperpolarization or depolarization activates the enzyme.
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