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Abstract:
Amphibian oocytes are physiologically arrested at the G2/M border of the first meiotic prophase until progesterone triggers the resumption of the meiotic cell cycle. Within a few hours, immature oocytes are transformed by a process designated meiotic maturation into mature oocytes ready to be shed and fertilized (see Ref. 9 for review). In parallel to the well known nuclear changes, a profound reorganization of the plasma membrane takes place that is reflected by a marked reduction of the surface area (8), a near complete membrane depolarization, and a downregulation of virtually all transmembrane transport systems (see Ref. 15 for review). As a consequence of these changes, the plasma membrane of mature oocytes has an extremely low ionic permeability, in contrast to the plasma membrane of immature oocytes, which exhibits high permeability for ions.
