Electrical Potential Difference Across the Nuclear Membrane of the Starfish Egg. ∗

Abstract

An electrical potential difference has been demonstrated to exist across the membrane of the intact germinal vesicle of the starfish egg (Asterias forbesii). For the measurement of this P. D. non-polarizable microelectrodes (Ag-AgCl-sea water) 1-3μ in diameter, a potentiometer and a highly sensitive moving coil galvanometer were used. The eggs were placed in a hanging drop of sea water over a moist chamber, and the electrodes were introduced into the egg by means of a micromanipulator. The measurements were accurate to within one millivolt.

In attempting to enter the germinal vesicle, an invagination at the point where the pressure was applied by the microelectrode, and general flattening of the nucleus would be produced. As the latter was pierced by the electrode, the invagination and flattening, however, would suddenly disappear, the nucleus immediately resuming the original spherical form. This physical reaction constituted the visual criterion for the penetration of the germinal vesicle. Corol-lated with this criterion was the instantaneous deflection of the galvanometer as the electrode penetrated the nucleus.

The interior of the nucleus was always positive with respect to the cytoplasm or the sea water medium. The magnitude of the potential across the nuclear membrane varied from 4 to 21 mv., the average of over 100 recorded measurements being 10 mv. The size of the potential depended considerably upon the condition of the animals and the eggs. In eggs that were in relatively poor condition the potentials varied from 5 to 10 mv., whereas the measurements of eggs in good condition varied from 15 to 20 mv. The potentials were fairly constant in any series of measurements. The potentials were fairly constant in any series of measurements. The variations were rather in different animals collected at different times.