Australian National University

• BIOL 2174

• Tutorial assignments The extracellular medium of a mammalian cell has a Ca2+ concentration of 3.1 mM, whereas the cytosolic Ca2+ concentration is around 98.7 nM (Please note the different unit here). The resting membrane potential across the plasma membrane is -62.9 mV. What is the equilibrium potential of Ca2+ across the plasma membrane at 37°C? Please give your answer in mV. https://www.physiologyweb.com/calculators/nernst_potential_calculator.html You need to use the Nernst equation to calcualte this. You can check if your signs are correct by thinking about which way Ca2+ would like to move and how that would change the membrane potential if we started from a neutral situation. The correct answer is: 138.3 What are the driving forces acting on the Ca2+ ions, and in which direction do they act? Calcium is at higher concentration outside the cell than inside, so it has a concentrsation gradient driving movement into the cell. The membrane ptoential inside the cell is negative so that provides an eleictrical gradient also driving the ions into the cell. The correct answer is: concentration gradient driving Ca2+ inward and membrane potential driving Ca2+ inward Why does Ca2+ have little influence on the cell resting potential? (ie why is the resting membrane potential is different to the equilibrium potential of Ca2+ ) The ions with the greatest permeability have the largest affect on the membrane potential. Ca2+ has a low permeability at rest. The correct answer is: The membrane permeability of Ca2+ is much lower than for other ion types The following four questions rel