Important regulatory roles in growth and differentiation have been ascribed to K and Na. However, little is known about the cellular control and compartmentalization of these ions, chiefly because of technical problems. We have developed an experimental system which overcomes many of these problems. The system consists of: 1) the amphibian oocyte, a giant cell that undergoes a prolonged period of growth and development without division, 2) potential and ion-selective microelectrodes to measure transmembrane electrical potentials and intracellular activities, 3) cryomicrodissection to measure regional (nuclear and ooplasmic) concentrations and 4) an intracellular reference phase to measure diffusible concentrations. Using this system we will conduct a two phase study of Na and K during four stages of oogenesis in Xenopus laevis. In the first, descriptive, phase we will construct cation-oogenesis lines (Co-lines) to provide a diachronic picture of membrane and intracellular cation regulation during oogenesis. We will measure: 1) membrane resting potential (Em), 2) intracellular Na and K activities, and 3) nuclear and ooplasmic Na and K concentrations. From Em and activity measurements, we will calculate electrochemical potentials for Na and K and thus describe changes in ion transport during oogenesis. From activity and regional concentration measurements, we will calculate local Na and K activity coefficients and assess changes in intracellular ion economy during oogenesis. Long term trends and transients will be identified and correlated with specific developmental events. In the second, analytic phase, we will use electrophysiological and tracer flux analysis to identify membrane mechanisms underlying changes in Em and electrochemical potentials, and isothermal and isotopic analysis to elucidate intracellular mechanisms (e.g., shifts in ion binding or regional water solvency) underlying changes in nuclear and ooplasmic activity coefficients. The study is unique in using cryogenic-based methods for measuring intracellular cation parameters and in measuring membrane and intracellular determinants simultaneously during growth and differentiation.
| Reynhout, J K; Horowitz, S B; Lau, Y T (1994) Urea transport in frog oocytes: effect of osmotic stress and vasopressin. Chin J Physiol 37:93-6 |
| Lau, Y T; Reynhout, J K; Horowitz, S B (1994) Membrane permeability changes during Rana oocyte maturation. Experientia 50:606-9 |
| Horowitz, S B; Lau, Y T (1988) A function that relates protein synthetic rates to potassium activity in vivo. J Cell Physiol 135:425-34 |
