PHYSICAL MODEL OF NERVE AXON .2. ACTION POTENTIAL AND EXCITATION CURRENTS - VOLTAGE-CLAMP STUDIES OF CHEMICAL DRIVING FORCES OF NA+ AND K+ IN SQUID GIANT-AXON

  • 1 January 1979
    • journal article
    • research article
    • Vol. 11  (3) , 263-288
Abstract
An adsorption model of nerve axon was extended to account for the origin of membrane currents observed under voltage-clamp conditions. Differing from the Hodgkin-Huxley model, which attributes excitation solely to a change of ionic conductances of the membrane, the present model proposes that a layer of axoplasm attached to the membrane (axon cortex) can undergo conformational changes and modulate selectivity for mobile ions. A 2-step voltage-clamp study was made of the chemical driving forces of Na+ and K+ ions in squid giant axon. The forces were measured by determining the instantaneous current-voltage relation when membrane current is carried by Na+ only or K+ only. The chemical driving force varies as a function of time and does not agree with the Nernst relation during the early phase of excitation. Implications of the observations are discussed.