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The role of active transport in potassium reabsorption in the proximal convoluted tubule of the anaesthetized rat.
Author(s) -
Wilson R W,
Wareing M,
Green R
Publication year - 1997
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1997.sp022006
Subject(s) - reabsorption , chemistry , tubule , solvent drag , paracellular transport , potassium , convoluted tubule , biophysics , passive transport , transepithelial potential difference , water transport , endocrinology , medicine , ion transporter , biochemistry , kidney , permeability (electromagnetism) , sodium , water flow , membrane , biology , microstructure , organic chemistry , environmental engineering , grain boundary , engineering , crystallography
1. We have previously assessed the contributions of diffusion and convection to net potassium reabsorption in the rat proximal convoluted tubule (PCT). The present study was conducted to evaluate the role of active transport in convective potassium reabsorption by measuring the transepithelial potassium reflection coefficient (sigmaK) in the presence and absence of cyanide in anaesthetized rats previously prepared for in vivo microperfusion. 2. Osmotic water permeability (Pf) was measured in double‐perfused tubules (lumen and peritubular capillaries) by manipulating the applied transepithelial osmotic gradient between ‐30 and +40 mosmol (kg H2O)(‐1) using raffinose added to or subtracted from luminal perfusates. Pf was unaffected by the presence of cyanide when the estimated dissipation of osmotic gradients along each tubule were taken into account. 3. The proportion of K+ (and Na+) convectively transported with water fluxes (i.e. sigmaK) was not affected by cyanide. In the absence of active transport and following correction for any diffusive component, sigmaK was 0.56 +/‐ 0.13, indicating substantial solvent drag which probably occurs via the paracellular pathway. 4. However, cyanide caused a reduction in net potassium flux over the entire range of fluid fluxes used in double‐perfusion experiments. Subsequent single‐perfusion experiments (tubule lumen only) using the specific K+‐H+‐ATPase inhibitor, SCH28080, failed to reveal any direct evidence for a primary active K+ transporting mechanism involved in K+ reabsorption in the PCT.