Developmental changes in rabbit proximal straight tubule paracellular permeability

Area of Science:

• Nephrology
• Physiology
• Renal Physiology

Background:

• The early proximal tubule reabsorbs organic solutes and bicarbonate, leading to a higher luminal chloride concentration than in blood.
• In adults, NaCl reabsorption in the late proximal tubule is equally divided between active transcellular and passive paracellular pathways.

Purpose of the Study:

• To investigate the passive chloride transport characteristics and permeability properties of adult and neonatal proximal straight tubules (PST).
• To understand the maturational changes in the paracellular pathway of the PST.

Main Methods:

• In vitro microperfusion of adult and neonatal rat proximal straight tubules.
• Measurement of net passive chloride flux and chloride permeability.
• Assessment of bicarbonate, mannitol, and sucrose permeabilities.
• Determination of transepithelial resistance using current injection and cable analysis.

Main Results:

• Neonatal PST showed no significant net passive chloride transport and chloride permeability not different from zero, unlike adult PST.
• Bicarbonate permeability was significantly lower in neonatal PST compared to adults.
• Neonatal PST exhibited higher sodium-to-chloride and bicarbonate-to-chloride permeability ratios.
• Transepithelial resistance was higher in neonatal PST (11.3 Omega x cm(2)) than in adult PST (6.7 Omega x cm(2)).

Conclusions:

• Significant maturational changes occur in the PST paracellular pathway affecting ion transport.
• Neonatal PST demonstrate immature passive chloride and bicarbonate transport mechanisms.
• These developmental differences in the PST paracellular pathway are crucial for understanding renal function maturation.