The potential across the resting membrane using the given Nernst equation under two assumptions- (1) Membrane potential is solely due to K + (2) Membrane potential is solely due to Na +

As given in the problem statement, when an electrode is stuck into an intact giant axon of the squid, the membrane potential is -70 mV. When the axon is suspended in seawater and stimulated to conduct a nerve impulse, there is a transient change in the membrane potential from -70 mV to +40 mV. Thus, -70 mV is the resting potential and +40 mV is the action potential. Refer Table Q11-1, “Ionic composition of seawater and of the cytosol in the squid giant axon” in the textbook. It shows the Na⁺ and K⁺ concentrations in the axon cytosol as well as in seawater.

Given,

For univalent ions and at 293K, the Nernst equation reduces to-

V= 58mV × log(CoCi)

1. 1. Calculate the potential across the resting membrane assuming that it is solely due to K⁺ ions

The expected membrane potential across resting membrane can be calculated using Nernst equation-

V =  58mV × log(CoCi)    = 58mV × log(9 mM344 mM)<