Influence of exogenous ions on the events of maturation in Rana pipiens oocytes

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Abstract
Full‐grown ovarian oocytes removed from non‐hormone‐treated Rana pipiens females exhibit a low level of protein synthesis, the rate of which is dependent upon the ionic environment. The highest rates of protein synthesis in these oocytes are obtained in media containing either a divalent cation (Ca++ or Mg++) or high levels of K+. The dependence of protein synthesis on ionic environment persists through about the first 18‐24 hours of maturation (at 18°C). Normal maturation of oocytes in vitro also has specific ionic requirements for the first 24 hours. In this case, the process requires high ionic strength (T/2 = 1.0‐1.2) and divalent cations. The kinetics of K+ exchange suggest that K+ exists in the ovarian oocyte in two compartments; one in equilibrium with the exogenous medium and freely exchangeable; the other in equilibrium with the exogenous medium and freely exchangeable; the other in equilibrium with the first internal compartment and only very slowly exchangeable. The slowly exchangeable (bound) compartment contains about 95% of all endogenous K+. In hormone stimulated oocytes, the kinetics of K+ exchange are essentially the same. Oocyte adaptation to ionic environment is discussed as a possible regulatory mechanism during maturation.