Question

Write a paragraph of 3-5 sentences answering the following questions. Your response should first answer the question and then go onto state physiological interpretation's behind your answer.

Assume a cell has a membrane potential of -70 mV and a Cl- equilibrium potential of -81 mV. If the cell membrane is permeable to Cl-, will there be net movement of Cl- into or out of the cell? Explain your answer.

Answer 1

Membrane potential of - 70mv means that inside membrane is negative at - 70mv than outside.

This membrane potential is formed by efflux of k ions, and by Na k pump.which pumps three Na ions out and 2 K ions inside.

Membrane potential of cell is equal to Equilibrium potential of K ions as it is more permeable and k conductance dominates.

Normally cell membrane is weakly permeable to chloride ions. And equilibrium potential of Cl is nearly equal to membrane potential, hence chloride does not affect membrane potential.

But if membrane is permeable to chloride ions and its equilibrium potential is different than membrane potential then cell potential can be calculated from the Goldman–Hodgkin–Katz equation. Which is used in multiple ion system.

In above case chloride ions will not move on either side as in multi-ion systems, there are areas of the cell membrane where the summed currents of the multiple ions will equal zero.and it is membrane potential which reverses direction not the equilibrium potential.