Growth-related renal type II Na/Pi cotransporter.

Area of Science:

• Nephrology
• Molecular Biology
• Physiology

Background:

• Nutrient retention is vital for growth, with the kidney playing a key role in maintaining positive external balance.
• Understanding renal nutrient transport mechanisms is essential for comprehending growth regulation.

Purpose of the Study:

• To isolate and characterize a novel growth-related sodium-dependent inorganic phosphate (P(i)) cotransporter from the kidney.
• To elucidate the functional and localization properties of this new cotransporter, designated type IIc.

Main Methods:

• cDNA isolation from human and rat kidney.
• cRNA microinjection into Xenopus oocytes to assess transport activity.
• Electrophysiological studies to determine transport mechanism (electrogenic vs. electroneutral).
• Northern blotting and immunohistochemical analysis for transcript and protein localization.

Main Results:

• Isolated a cDNA encoding a growth-related Na(+)-dependent inorganic phosphate (P(i)) cotransporter (type IIc).
• Demonstrated Na(+)-dependent P(i) cotransport activity with high affinity (0.07 mM) and extracellular pH dependence.
• Type IIc Na/P(i) cotransport was found to be electroneutral, contrasting with the electrogenic type IIa.
• Type IIc transcript and protein were predominantly expressed in the kidney of weaning animals, localized to the apical membrane of proximal tubular cells.

Conclusions:

• Type IIc is a growth-related renal Na/P(i) cotransporter with high P(i) affinity and an electroneutral transport mechanism.
• Its expression and function are prominent in weaning animals, suggesting a critical role during periods of rapid growth.
• The transporter's role appears diminished in adult animals.