Among EK, ENa, and ECa, which has the most positive equilibrium potential?

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Multiple Choice

Among EK, ENa, and ECa, which has the most positive equilibrium potential?

Explanation:
The main idea is that an ion’s equilibrium potential is set by its electrochemical gradient, described by the Nernst equation. E_ion = (RT/zF) ln([ion]outside/[ion]inside). The bigger the gradient and the higher the ion’s valence, the more positive (or negative) the equilibrium potential. Potassium has a large intracellular concentration versus extracellular, and with a single positive charge, its E_K is around -90 mV. Sodium has a much larger extracellular-to-intracellular gradient with a single positive charge, giving E_Na near +60 mV. Calcium, however, has a much smaller intracellular concentration (very low inside) and a relatively high extracellular concentration, and it carries a double positive charge (+2). This combination produces a very large positive E_Ca, around +120 mV. Therefore, among these ions, the calcium equilibrium potential is the most positive.

The main idea is that an ion’s equilibrium potential is set by its electrochemical gradient, described by the Nernst equation. E_ion = (RT/zF) ln([ion]outside/[ion]inside). The bigger the gradient and the higher the ion’s valence, the more positive (or negative) the equilibrium potential.

Potassium has a large intracellular concentration versus extracellular, and with a single positive charge, its E_K is around -90 mV. Sodium has a much larger extracellular-to-intracellular gradient with a single positive charge, giving E_Na near +60 mV. Calcium, however, has a much smaller intracellular concentration (very low inside) and a relatively high extracellular concentration, and it carries a double positive charge (+2). This combination produces a very large positive E_Ca, around +120 mV.

Therefore, among these ions, the calcium equilibrium potential is the most positive.

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