Teleost Fh14-3-3a protein protects Xenopus oocytes from hyperosmolality.
We have previously cloned and characterized a novel 14-3-3 gene from the euryhaline telost Fundulus heteroclitus, Fh14-3-3a (Kültz et al., 2001). The corresponding gene product is osmoregulated and most highly expressed in gill epithelium of this fish. In the present study we have expressed Fh14-3-3a cRNA in Xenopus laevis oocytes and investigated the survival and electrophysiological parameters of Xenopus oocytes in isosmotic and various hyperosmotic media. Xenopus oocytes expressing Fh14-3-3a show no mortality after a 16 hour exposure to hyperosmolality in the form of elevating medium K(+), Na(+), polyethylene glycol, or sorbitol concentrations up to 444 mosmol/kg. In contrast, 16 hours of the same hyperosmolality caused 100% mortality in control Xenopus oocytes injected with water. As a result of hyperosmolality the Xenopus oocyte membrane potential decreased between 10 and 70% in oocytes expressing Fh14-3-3a whereas it was completely abolished in control oocytes. We report that one potential cause for the osmoprotective effect of Fh14-3-3a on Xenopus oocytes could be its inhibition of an endogenous chloride current. Hyperosmotic urea was not as harmful to Xenopus oocytes as hypertonicity and maybe acting through a different mechanism. Coexpression of Fh14-3-3a with a human calcium channel in Xenopus oocytes did not affect the electrophysiological properties of this exogenous channel. Thus, the osmoprotective effect of Fh14-3-3a may prove a valuable tool for the characterization of exogenous ion channels in Xenopus oocytes exposed to hyperosmotic conditions.
Kohn
Andrea
A
Whitney Laboratory, University of Florida, St. Augustine, Florida 32080, USA.
Chakravarty
Devulapalli
D
Kültz
Dietmar
D
D048948:14-3-3 Proteins; D000818:Animals; D030801:Animals, Genetically Modified; D002462:Cell Membrane / Q000502:physiology; D003001:Cloning, Molecular; D005260:Female; D029941:Fish Proteins / Q000378:metabolism*; D023781:Fundulidae; D006982:Hypertonic Solutions; D017136:Ion Transport / Q000502:physiology; D008564:Membrane Potentials / Q000502:physiology*; D009865:Oocytes / Q000502:physiology*; D009994:Osmolar Concentration; D018075:RNA, Complementary; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism*; D014882:Water-Electrolyte Balance / Q000502:physiology*; D014982:Xenopus laevis
D048948:14-3-3 Proteins; D029941:Fish Proteins; D006982:Hypertonic Solutions; D018075:RNA, Complementary; D014446:Tyrosine 3-Monooxygenase