Using a methodology that combines two new techniques; ultra-low temperature microdissection (ULTM) and the intracellular reference phase (RP) we have been able to unambiguously demonstrate sodium, potassium and water binding in amphibian oocytes. Furthermore, we have described the quantitative functions that relate "free" and "bound" cytoplasmic Na ion, K ion and water in full grown oocytes at 1st meiotic prophase. Both cytoplasmic adsorption mechanisms and the cell membrane importantly determine intracellular cation levels in these cells. In this proposal, we follow intracellular cation kinetics and equilibria during progesterone-induced meiotic maturation, uing RP-ULTM, to establish: (1) the mechanism of progesterone action, and (2) the quantitative role that transport and adsorption play in maturation. These studies directly reflect not only the mechanism of hormone action, and oogenesis but matters as diverse as cellular membrane potentials, chemical activities, nucleocytoplasmic solute asymmetries and the interpretation of exchange kinetics.