Teruo Yamasaki

The effects of potassium and sodium ions on the resting and action potentials of the cockroach giant axon

Abstract The effects of varying the potassium and sodium concentrations in the bathing fluid on the resting and action potentials of the cockroach giant axon have been examined by means of intracellular microelectrodes. Plotting the resting potentials against the logarithms of the external potassium concentrations resulted in a straight line in the concentrations higher than about 20 mM. The decrease in the sodium concentration had no appreciable effect on the resting potential, but effectively depressed the action potential. Plotting the reversed potentials against the logarithms of the external sodium concentrations resulted in a straight line, which diverged only slightly from the theoretically expected straight line having a slope of 59 mV for a tenfold change in sodium. The rate of rise of the action potential was decreased very effectively by the sodium-deficient solution. It can safely be said that the overall result constitutes strong evidence for the essential validity of the sodium theory in the cockroach giant axon.

Synaptic transmission in the last abdominal ganglion of the cockroach

Abstract Excitatory postsynaptic potentials (e.p.s.p.s) were recorded from the last abdominal ganglion of the cockroach. The e.p.s.p. was much increased and prolonged by anticholinesterases, and such a change in e.p.s.p. was found to be responsible for the prolonged synaptic after-discharge. It was found that inactivation of cholinesterase runs parallel with these changes in electrical responses under the influence of anticholinesterases. The sensitivity of the ganglion to applied acetylcholine was increased by desheathing and eserinization. Three possible explanations for the nature of transmitter substance were suggested; the possibility of acetylcholine as transmitter still remains.

Electrical properties of the cockroach giant axon

Abstract The electrical properties of the cockroach giant axons have been examined by means of intracellular microelectrodes. Membrane resistance and membrane capacity were estimated by recording electrotonic potentials produced by square pulses of polarizing current. The membrane capacity was found to be relatively high as compared with other kinds of nerve fibres. A delayed rectification was observed with a strong cathodal current. The maximum rate of rise of the action potential was decreased by depolarization, whereas it underwent little change by hyperpolarization. The changes in after-positivity and after-negativity under electrotonus suggest that the mechanisms of their production are different. The inward sodium current during an impulse was calculated on the basis of the sodium theory. The peculiarities of the electrical properties of the roach giant axon are discussed.