Estimated potassium reflection coefficient in perfused proximal convoluted tubules of the anaesthetized rat in vivo

• Published in: The Journal of physiology Vol. 488; no. Pt 1; pp. 153 - 161
• Main Authors: Wareing, M, Wilson, R W, Kibble, J D, Green, R
• Format: Journal Article
• Language: English
• Published: England The Physiological Society 01-10-1995
• Subjects: Anesthesia; Animals; Biological Transport - physiology; Epithelium - metabolism; Epithelium - ultrastructure; Inulin; Ion Channels - metabolism; Kidney Tubules, Proximal - cytology; Kidney Tubules, Proximal - metabolism; Kidney Tubules, Proximal - ultrastructure; Male; Potassium - metabolism; Raffinose - pharmacology; Rats; Rats, Sprague-Dawley; Sodium - metabolism; Tritium; Water - metabolism
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.1995.sp020953

1. As yet there is no definitive description of the mechanism and route by which K+ reabsorption is achieved in the proximal
convoluted tubule (PCT). We have assessed the contribution of convective K+ transport to net potassium ion flux (JK) by estimating
the reflection coefficient of K+ (sigma K) in the proximal tubule of anaesthetized rats previously prepared for in vivo microperfusion.
2. Alterations in the luminal concentration of the impermeant solute raffinose in single-perfused (lumen only) and double-perfused
(lumen and capillaries) PCTs were found to change fluid reabsorption in a predictable fashion. 3. Net potassium ion flux (JK)
in single- and double-perfused tubules was significantly correlated with net fluid flux (Jv), suggesting that convective K+
transport may be a significant factor in overall K+ transport by the PCT. 4. Estimates of sigma K in single- and double-perfused
tubules were very similar (0.14 +/- 0.06 and 0.13 +/- 0.05, respectively), even though K+ diffusion was not strictly controlled
in the former group. The maximum effect of 'pseudo-solvent' drag in double-perfused tubules was estimated to give a sigma
K of 0.40. This low value for sigma K suggests that true convection/solvent drag may be an important driving force for the
reabsorption of K+ from the PCT of the rat.