Molecular Biology Of The Cell 6th Edition by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morgan, Martin Raff, Keith Roberts, Peter Walter

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0 The giant axon of the squid (Figure Q11-3) occu- pies a unique position in the history of our understanding of cell membrane potentials and nerve action. When an electrode is stuck into an intact giant axon, the membrane potential registers -70 mV. When the axon, suspended in a bath of seawater, is stimulated to conduct a nerve impulse, the membrane potential changes transiently from -70 mV to +40 mV. For univalent ions and at (293 K), the Nernst equation reduces to where are the concentrations outside and inside, respectively. Using this equation, calculate the potential across the resting membrane (1) assuming that it is due solely to and (2) assuming that it is due solely to and concentrations in the axon cytosol and in seawa- ter are given in Table Q11-1.) Which calculation is closer to the measured resting potential? Which calculation is closer to the measured action potential? Explain why these assumptions approximate the measured resting and action potentials.