Permeability of the Nuclear Membrane to Vital Stains

Abstract

The staining of the nucleus has been considered in general as a sign of decreased vitality of the cell leading to its death. In spite of that we find in the literature a few reliable data indicating that vital staining of the nucleus may occur. This has been accomplished by immersing living cells in solutions of various dyes, both of plants and of animals. It has also been accomplished by micro-injecting various dyes, especially the sulphonated pH indicators of Clark and Lubs into amoebae and tissue culture cells. The stain blown against the nuclear membrane is taken up by the nucleus, but after a short time the color disappears. The possibility at least of a transitory vital staining of the nucleus seems to be fairly well established.

It was of interest to note whether the nucleus is stainable by any dye or only by certain groups of dyestuffs, that is to say, the question was: whether the nuclear membrane is selective or freely permeable. In order to test this it was necessary to micro-inject directly into a cell, since it is well known that many dyestuffs do not penetrate living cells from the environment.

Amoeba dubia and A. proteus were selected for the experiments. Aqueous solutions of the stain were blown by means of a micropipette into the cytoplasm directly against the nucleus without injuring its wall. The staining of the nucleus was considered as vital only when the amoeba recovered completely. When the amount injected was very small it was possible to get the staining of the nucleus only, but when the amount was larger the surrounding cytoplasm was also stained. About 40 different dyes were used and in all cases in which a vital staining of the nucleus occurred the color was transitory, fading away sooner or later.