Question

1. A cell has a resting membrane potential of -70mV. In each of the following cases, would the cell depolarize, or hyperpolarize? Justify your answers with a written explanation that relates to the GHK equation; you do not need to calculate new membrane potentials, but you should explain why the changes would occur. Hint: Use the simulations from class to solve these

   1. Cell becomes more permeable to Cl-

   2. Cell becomes more permeable to Ca++ (Hint: which ion shown in the simulation has distributions most similar to that of calcium in the ECF and cytosol?)

   3. A considerable amount of K+ is injected into the cytoplasm of the cell such that the concentration increases 1000-fold

Answer 1

If postassium is injected into the cytoplasm of the cell then concentration of intracellular k+ increases and extracellular K+ decreases which leads to more negative resting potential means hyperpolarize state.
Kin is greater than Kout.
On the other hand, Cl- is negatively charged. Thus the increase in Cl in would increase Cl- outflux, that is, would lead to loss of negative charges and depolarization. The overall effect of inserting K+ in cytoplasm depends on K+ and Cl- concentrations inside and outside the cell, and on relative permeabilities of the membrane for the two ions.
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