Action potential and non-linear current-voltage relation in starfish oocytes.

1. The electrical properties of the oocyte membrane of the starfish, Asterina pectinifera, were investigated using an intracellular microelectrode. 2. The resting potential in artificial sea-water ranged from -70 to -80 mV. 3. The starfish oocyte membrane was capable of generating an action potential as a result of permeability increases to both Ca and Na ions.4. The Ca component of the action potential was reversibly suppressed by Co or Mg ions, while the Na component was not affected by tetrodotoxin 5 times 10-minus 6 g/ml. 5. The steady-state relation of voltage vs. current was not linear but S-shaped. The curve wascomposed of inward-going rectification at the membrane potential more negative than -65 mV, outward-going rectification at the potential more positive than OmV and the transitional region between them. These findings are compared with those obtained in the mature egg of the tunicate.