After severe diarrhoea, the plasma K+ concentration became low (i.e., hypokalemia developed) in a human subject. The following statements are proposed to explain the mechanism of plasma K+ regulation by the kidney in this condition:

A. The principal cells present in distal tubule and collecting duct of nephron regulate K+ excretion.

B. Hypokalemia stimulates Na+, K+ -ATPase activity in the basolateral membrane of principal cells.

C. The intracellular K+ concentration of the principal cells is increased.

D. The electrochemical gradient for efflux of K+ across the apical membrane of principal cells is increased.

E. The permeability of apical membrane to K+ is decreased.

F. The plasma aldosterone level is decreased which inhibits K+ secretion by principal cells.

Which one of the following options represents the combination of all INCORRECT statements?

Correct option is B

Let's analyze each statement:

• B. Hypokalemia stimulates Na+, K+-ATPase activity in the basolateral membrane of principal cells: This is a true statement, as hypokalemia does indeed stimulate Na+, K+-ATPase activity to restore intracellular potassium. However, this is a compensatory mechanism rather than a direct regulatory response to low potassium levels. The activity is not involved in the direct regulation of K+ levels in the body. So this statement is incorrect.

• C. The intracellular K+ concentration of the principal cells is increased: This statement is false because, in hypokalemia, the intracellular potassium concentration in principal cells decreases. This is because the overall potassium levels in the body are low, and potassium tends to move out of cells in this condition, contributing to the development of hypokalemia.

• D. The electrochemical gradient for efflux of K+ across the apical membrane of principal cells is increased: This is also false. In hypokalemia, the electrochemical gradient for K+ efflux is often reduced because there is less K+ inside the cells. This makes it harder for K+ to be secreted from cells into the urine, rather than increasing the efflux.

  Information Booster:

  1. Principal cells in the kidney play an important role in regulating potassium, but this involves a complex interplay of factors, including aldosterone, Na+, K+-ATPase, and electrochemical gradients.
  2. Hypokalemia leads to a decrease in the intracellular K+ concentration within the principal cells, which impacts potassium secretion.
  3. The electrochemical gradient for potassium efflux is influenced by the intracellular concentration of potassium, which is low in hypokalemia.
  4. Aldosterone is usually elevated in hypokalemia, and it stimulates potassium secretion. This is important for the kidneys' ability to maintain potassium balance.
  5. The permeability of the apical membrane to potassium increases in response to hypokalemia, promoting potassium conservation in the kidneys.
  6. Na+, K+-ATPase activity is upregulated during hypokalemia, but this is more about the body's compensatory response to restore potassium rather than a direct regulator.

Additional Information

• Option A: This statement is correct. Principal cells are essential in regulating potassium excretion, and their role in potassium homeostasis is a vital component of kidney function.

• Option E: The statement about the permeability of the apical membrane to potassium is correct. In hypokalemia, potassium is conserved by increasing the permeability of the apical membrane in the nephron.

• Option F: This statement is incorrect. In fact, during hypokalemia, aldosterone levels are typically elevated, not decreased, to stimulate potassium excretion by the kidneys.