SM 191a/192a - Functions of the Renal Tubules I and II

Question 1

Activation of the CaSR [downregulates/upregulates] flow through the Na+/K+/2Cl- cotransporter

Explain

Answer 1

Activation of the CaSR downregulates flow through the Na+/K+/2Cl- cotransporter

This decreases the + to - gradient generated by the cotransporter that pulls Ca2+ into the interstitum, thus reducing the force that drives Ca2+ reabsorption

Question 2

How is the inner-medullary collecting duct similar to the cortical collecting duct?

How is it different?

Answer 2

• Similar:
  
  • Na+ reabsorption pathway
  • K+ secretion pathway
  • Na+ reabsorption and K+ secretion are reciprocal
  • Water channels responsive to ADH
• Different:
  
  • Medullary has ANP receptor on basolateral membrane; when bound to ANP, inhibits Na+ reabsorption
    
    • Promotes naturesis
  • Medullary has Urea transporter on apical membrane; reabsorbs urea, recycled back into the interstitium
    
    • Contributes to high interstitial osmolality

Question 3

Competition for which transport protein leads to many drug-drug interactions?

Answer 3

P-gp

In the proximal convoluted tubule
(the primary site of secretion for drugs and drug metabolites)

Question 4

Where in the kidney tubule does transcellular Ca2+ reabsorption occur?

Through which protein?

Answer 4

Distal covoluted tubule

• Apical
  
  • TRPV5 channel
• Basolateral
  
  • Ca2+/3Na+ exchanger
    
    • Driven by Na+ gradient into the cell

Question 5

What are the effects of aldosterone binding to its cytoplasmic receptor?

Answer 5

Aldoserone/receptor complex is transported to the nucleus

• Acts as a transcription factor
  
  • More Na+/K+ ATPases
  • More ENaC (Na+ channels)
  • More ROMK (K+ channels)
• -> increased Na+ reabsorption, K+ secretion via…
  
  • Short-term mechanisms
    
    • Increased SGK1 activity -> phosphorylates NEDD-2
    • P-NEDD-2 cannot retrieve ENaC from the membrane
    • => More ENaC to reabsorb Na+
  • Later mechanisms
    
    • Increased surface area of basolateral membranes
    • -> Inreased Na+/K+ ATPase activity