Electric Properties of Echinoderm Eggs

For many years, it has been believed that there is practically no potential differenee across the plasma membrane in echinoderm eggs (TAYLOR and WHITAKER, 1926; GELFAN, 1931; ROTHSCHILD, 1938; KAMADA and KINOSITA, 1940; SCHEER, MONROY, SANTANGELO and RICCOBONO, 1954).However, according to ROTHSCHILD and BARNES (1953), the concentration of potassium is 21-fold high.er in the protoplasm of the sea urchin egg than in the outside sea water.If this ionic asymmetry is associated with a potential difference across the plasma membrane just as in many other cells, a potential of about 80 mV, inside negative, is expected (cf.TYLER, MONROY, KAO and GRUNDFEST, 1936).Previously, information on the electric properties in echinoderm eggs has been obtained by measurements in egg suspensions (cf.COLE and CURTIS, 1930).This method is, however, not suitable for an accurate measurement of membrane resistance when the specific conductivity of the medium is as high as that of sea water.Moreover, in such experiments, membrane potential cannot be measured.Using ultra-microelectrode technique recently advanced in the field of electrophysiology, LUNDBERG (1955) andTYLER et al. (1956) determined the membrane potential and the membrane resistance.However, as far as the membrane potential was concerned, quite different results were obtained between the two investigations.The discrepancy of the results gave an impetus for the present paper.Preliminary notes on this experiment have been presented elsewhere ( KIRAMOTO, 1958( KIRAMOTO, , 1959)).