Membrane ionic current of the propagated action potential. A new method.

Since HODGKIN et al. (1949) first recorded membrane ionic currents by the technique of voltage clamping the membrane of squid giant axons, it has been possible to predict precisely the ionic currents produced by an action potential. However, the ionic current produced during the propagating action potential can be obtained only after intricate experiments and laborious calculations. Employing the method used in the present report, the relationship between ionic current and membrane potential of nerve and muscle fibers can easily be obtained. According to the cable equation, the ionic current is described as the difference between the first and second derivatives of the action potential. It is also calculated that the ionic current should be zero at the foot of the action potential. Applying this condition to the cable equation, the ionic current-membrane voltage relation can then be obtained from the electronically differentiated transmembrane action potential. The fact that this method can be applied to muscle fibers whose membrane structure is complicated due to the tubular system is also discussed.