A study of the crustacean axon repetitive response. I. The effect of membrane potential and resistance.

Abstract

AbstractThe transmembrane electrical properties of the crustacean axon have been examined by a new technique which allows for quantitative evaluation of the electrical and excitable characteristics across a microscopic area, “patch,” of fiber membrane using external electrodes. Data from repetitive firing and from non‐repetitive firing fibers compare as follows: (1) Membrane potential, resting, 82 mv repetitive; 67 mv non‐repetitive; 70–75 mv transition level repetitive to non‐repetitive. (2) Membrane potential, active, 132 mv, 50 mv overshoot repetitive; 100–120 mv, 30–50 overshoot, non‐repetitive. (3) Membrane resistance, 7.6 × 106 ohms or 2300 ohms cm2 repetitive; 2.8 × 106 ohms or 880 ohms cm2 non‐repetitive. (4) Membrane time constant, 2.5 ms repetitive; 1.5ms non‐repetitive. (5) Membrane capacity 1.0μf repetitive; 1.7 μf non‐repetitive. (6) Repetitive firing property may be restored to non‐repetitive axons by increasing the Vm value with a polarizing inward current. This increases Rm also. (7) Non‐repetitive fibers show considerable inactivation, give rise to “more or less” spikes particularly during refractory period following a spike, and respond to anode‐break stimulation. Repetitive firing axons do not. (8) The action potential has two active components, one to depolarize (sodium) one to repolarize (potassium), both of which drive the membrane potential. toward predetermined levels. (9) The repetitive firing axons show little or nc inactivation with weak prolonged depolarization producing trains of spikes. There is a slow rise in critical firing level which ultimately causes the spike train termination. There is a slow increase in the undershoot (diphasic repolarization) amplitude.