AJP - Cell Physiology, Vol 238, Issue 3 133-C138, Copyright © 1980 by American Physiological Society
Potassium exchange in the whole cell, cytoplasm, and nucleus of amphibian oocytes
M. Frank and S. B. Horowitz
Potassium isotope exchange was studied in whole oocytes, with and without
ovarian follicles, and in oocyte cytoplasm and nucleus. Cryomicrodissection
was used to prevent solute redistribution during nuclear and cytoplasmic
separation. Manual follicle removal causes a small decrease in the K+ of
the preparation. No effect of follicle removal is seen on 42K+ exchange.
Whole oocyte exchange is multiphasic and reflects the presence of two
intracellular K+ fractions. One of these fractions is present in both
nucleus and cytoplasm. It exhibits first-order exponential kinetics,
apparently established at the cell membrane. The second fraction is
restricted to cytoplasm and exchanges at an imperceptible rate. The
fractions differ in pre- and posthibernation oocytes. These observations
clarify the mechanism whereby nuclear/cytoplasmic K+ concentration
asymmetries are maintained and the mechanisms responsible for the high
K+-activity coefficient previously reported in these cells.
