Abstract
Fully grown oocytes of Xenopus laevis undergo resumption of the meiotic cycle when treated with the steroid hormone progesterone. Previous studies have shown that meiotic maturation results in pro-found downregulation of specific endogenous membrane proteins in oocytes. To determine whether the maturation impacts the functional properties of exogenously expressed membrane proteins, we used cut-open recordings from Xenopus oocytes expressing several types of Na+ and K+ channels. Treatment of oocytes with progesterone resulted in a downregulation of heterologously expressed Na+ and K+ channels without a change in the kinetics of the currents. The time course of progesterone-induced ion channel inhibition was concentration dependent. Complete elimination of Na+ currents temporally coincided with development of germinal vesicle breakdown, while elimination of K+ currents was delayed by ∼ 2 h. Coexpression of human β1-subunit with rat skeletal muscle α-subunit in Xenopus oocytes did not prevent progesterone-induced downregulation of Na+ channels. Addition of 8-bromo-cAMP to oocytes or injection of heparin before progesterone treatment prevented the loss of expressed currents. Pharmacological studies suggest that the inhibitory effects of progesterone on expressed Na+ and K+ channels occur downstream of the activation of cdc2 kinase. The loss of channels is correlated with a reduction in Na+ channel immunofluorescence, pointing to a disappearance of the ion channel-forming proteins from the surface membrane.
Original language | English (US) |
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Pages (from-to) | C677-C688 |
Journal | American Journal of Physiology - Cell Physiology |
Volume | 280 |
Issue number | 3 49-3 |
DOIs | |
State | Published - 2001 |
Externally published | Yes |
Keywords
- Cdc2 protein kinase
- Internalization
- Maturation
- Potassium channels
- Sodium channels
ASJC Scopus subject areas
- Physiology
- Cell Biology