PERMEABILITY OF NUCLEAR MEMBRANES

Our knowledge of the permeability and electrochemical properties of biological membranes has been greatly advanced in the past fifteen years by the development of intracellular electric measuring techniques. Such techniques, used until quite recently only in studies of surface (plasma) membranes, have now been applied to nuclear membranes. This paper summarizes briefly some of the results obtained in interphase nuclei of salivary gland cells and of egg cells. The method consists in essence of passing an electric current across the nuclear membrane from a microelectrode placed inside the nucleus and recording the resulting resistive voltage drops across this membrane with a second intranuclear electrode (FIGURE 1 ) . Current density is rather uniform over the nuclear membrane surface under these conditions; the conductance of unit membrane area can be determined rather accurately. Current densities of an order as low as amp. cm-2 and 10 msec. duration can be used for the measurements. Changes in normal ion composition around the membrane due to transfer of ionic charge are thus extremely small. This minimizes the risk of causing changes in membrane properties, and is a significant advantage over methods employing tracer particles in which the quantity or the nature of the tracer itself may alter the permeability of the membrane. A shortcoming of the method is that it yields only integrated values of permeability; in its present form it gives no information about the identity of the ions that carry the current.