An 18-year-old college student has just eaten a large container of fried rice. What is the renal cellular mechanism that prevents this sodium load from drastically increasing his plasma osmolality?
Increase in aquaporin gene expression by collecting duct cells
Movement of aquaporin channels to the apical surface of collecting duct cells
Receptor binding of atrial natriuretic peptide (ANP) in distal tubule cells
Receptor binding of spironolactone in distal tubule cells
Release of urodilatin by collecting duct cells
Correct answer
Movement of aquaporin channels to the apical surface of collecting duct cells
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correct answer: B
An increase in sodium intake will cause an increase in plasma osmolality, triggering the release of antidiuretic hormone (ADH), a.k.a. vasopressin. The immediate effect of ADH is movement of aquaporin channels to the apical surface of collecting duct cells (Choice B).
Increase in aquaporin gene expression by collecting duct cells (Choice A) is incorrect. Although this action is the long-term effect of ADH, an upregulation of gene expression occurs over a scale of days, not minutes.
Receptor binding of atrial natriuretic peptide (ANP) in distal tubule cells (Choice C) is incorrect. ANP is released by the atria of the heart in response to an increase in blood volume, and acts on the collecting duct cells to decrease NaCl and water reabsorption. This would not decrease plasma osmolality.
Receptor binding of spironolactone in distal tubule cells (Choice D) is incorrect. Spironolactone is an exogenous medication that effects a diuresis by antagonizing the aldosterone receptor in cortical collecting tubules. This would not decrease plasma osmolality.
Release of urodilatin by collecting duct cells (Choice E) is incorrect. Urodilatin is a peptide produced by the distal tubule collecting duct in response to an increase in blood pressure/volume. It causes local inhibition of NaCl and water reabsorption; this would not decrease plasma osmolality.