Question

Kidney cells respond to vasopressin (or ADH) by means of a G-protein and PKC mediated mechanism. How would a cell’s response to vasopressin be affected if the extracellular calcium concentration was reduced to 0.5 mM?

A. The cells would no longer respond to vasopressin

B. Response to vasopressin would be unaffected

C. Response to vasopressin would be much faster

D. Response to vasopressin would be significantly weakened

*****B. Is not the Correct Answer*****

Answer 1

Answer- Response to vasopressin will be significantly weakened.

Explanation- Activation of vasopressin receptors activaates phospholipase C, which causes the hydrolysis of inositol 4,5-bisphosphate to IP3 and DAG. These second messenger system activate enzymes, such as PKC, and mobilize intracellular calcium stored in the endoplasmic reticulum. Emptying of calcium stores stimulates trp cationic channels that allow ECF calcium to enter the cells. V2 receptors also interact with adenyl cyclase and generate cAMP as a second messenger which activates protein kinase and causes insertion of aquaporin-2 channels into the luminal cell membrane of collecting duct cells in the kidney.