Effects of Potassium and Sodium Ions on the Resting and Action Potentials of the Giant Axon of the Cockroach

Abstract

A KNOWLEDGE of the fundamental properties of the insect nerve is very useful in studying the mode of action of insecticides, many of which are nerve poisons. In order to verify the validity of the sodium theory1 in the cockroach giant axon2, the effects on the resting and action potentials of varying the sodium and potassium concentrations in the bathing fluid were examined with intracellular micro-electrodes. A compensation circuit for improving high-frequency responses was employed in place of the simple cathode follower circuit used in our previous study3. The following mean values for the membrane potentials were obtained from axons immersed in modified Ringer's solution containing sodium ions at a concentration of 214 mM : resting potential 70.3 mV.; action potential 94.5 mV.; positive phase 3.4 mV.; maximum rate of rise of action potential 1,113 V./sec.; maximum rate of fall 382 V./sec.