3. In the lecture, we learned that during an action potential Ca2+ concentration at the active zone can rise one-thousandfold, from 100nM to 100M. This has led to the development of all kinds of calcium indicators for optical readout of neuronal activities. You know that the movements of Na+and K+across the cell membrane constitutes the neuronal action potential. Therefore, you wanted to develop sodium and/or potassium indicators to detect action potentials. Question: Use simple calculations to show if it is feasible to detect intracellular changes of Na+and K+during an action potential. You may assume the neuron has a shape of sphere with 20m diameter, and the membrane capacitance per unit area is 1F/cm2. Assume the resting potential is 70mV. The initial concentrations of K+are 100mM/5mM, intra-/extra-cellular, Na+ being 15 mM/150mM, intra-/extracellular. Assume existing technologies can detect 1% change for Na+,0.1% for K+