Na + and K + uptake and exchange by the amphibian oocyte during the first meiotic division

Abstract

The uptake and efflux of 22Na and 42K were studied in denuded Rana pipiens oocytes following progesterone induction of the resumption of meiotic maturation. Coincident with the breakdown of the large nucleus, or germinal vesicle, there is a virtual disappearance of K + permeability of the oocyte plasma membrane. Only about 1–2% of the total [K +] i is exchanged by completion of nuclear breakdown (8–10 hr) and accounts for the finding that there is no detectable change in total [K +] i during the first meiotic division (20–24 hr). In the case of Na +, influx, exchange, and efflux kinetics were unchanged during the first meiotic division, with 20 and 35% of the total oocyte Na + exchanging by the completion of nuclear breakdown and first meiotic division, respectively. Removal of Na + from the incubation medium produced and earlier nuclear breakdown, whereas a K-free medium delayed breakdown. There was no effect of 10 μm/ml tetrodotoxin or 10 −5 M strophanthidin on the time course of nuclear breakdown. Thus one action of progesterone appears to be a selective turning off of “K channels” in the oocyte plasma membrane. The disappearance of K selectivity of the oocyte plasma membrane coincides with plasma membrane depolarization, as well as nuclear swelling and breakdown.