Changes in Membrane Impedance associated with a Cortical Contraction in the Egg of Xenopus laevis

Abstract

ATTENTION has recently been drawn to the concept of the cell membrane as a transducer of external stimuli, mediating between environmental effectors and cyto-plasmic responses by altering the surface potential (refs. 1 and 2, and our own results which are in preparation). Alteration of the potential profile through the membrane, resulting from a change in electrostatic surface potential caused by changes in external ionic strength, adsorption of polyions or the close approach of cell surfaces, could lead to cytoplasmic reactions¹. Changes in membrane field might affect the conformation of membrane macro-molecules, leading to the presentation of new groups at the cytoplasmic interface. Alternatively, changes in permeability of the membrane might follow conformational changes, or else might occur in their absence. Any of these mechanisms could provide the cytoplasm with information about the external environment on which it might act accordingly. The possibility of co-operative phenomena in membranes, envisaged by Changeux and his colleagues^3,4, is of great interest in this respect, especially because the stimulus for co-operative change might be a change in membrane electrostatic field⁵.