Describe the factors that affect the flux of potassium across the cell membrane
Candidates were required to synthesize knowledge across a number of areas and have a
good overview of the topic. This included the following - Insulin (acts to up-regulate Na/K
ATPase activity promoting intracellular shift of potassium in adipose and muscle tissue);
catecholamines (beta2 stimulation up-regulates Na/K ATPase activity promoting
intracellular shift of potassium); aldosterone; pH (acidosis promotes H+/K+ exchange (via
H+/K+ antiport), and reduces the activity of the Na K ATPase pump); osmolality (cellular
dehydration increases intracellular K+ concentration promoting diffusion of potassium out
of the cells); exercise; plasma potassium; temperature.
Unlike most scenarios where the flux of something across a membrane is being asked about, this time it appears the examiners did not expect something brutally stupid like a rote-learned recitation of Fick's Law of diffusion. Or, at least, from a reading of their answer, one develops the impression that genuinely relevant factors were being asked about. Mechanisms governing the transcellular movement of potassium account for 90% of our medical strategies for the management of hyperkalemia, and it would have been a pity to waste that question on something like the Gibbs Donnan effect.
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