Mechanisms of Fluid Transport Across Renal Tubules

The sections in this article are: 1 Theoretical Foundations of Water Transport in Epithelia 2 Volume Absorption in the Proximal Tubule 3 Water Permeability of the Proximal Tubule 3.1 Measurement of Water Permeability 3.2 Importance of the Osmotic Water Permeability 4 Location of the Osmotic Gradient 4.1 Luminal Hypotonicity Produced by Solute Absorption 4.2 Absorbate Hypertonicity 5 “Passive” Driving Forces for Volume Absorption 5.1 NaCl Diffusion in Volume Absorption 5.2 Reflection Coefficient Differences 6 Models of Solute-Solvent Coupling in Proximal Volume Absorption 7 Routes of Volume Movement in the Proximal Nephron 7.1 Measurement of Cell Membrane Osmotic Water Permeabilities 8 Consequences of Transcellular Volume Flow 9 The ADH-Sensitive Distal Nephron 9.1 Measurement of Permeability Changes Produced by ADH 9.2 Wafer Permeability of ADH-Sensitive Nephron Segments in Vivo and in Vitro 10 Site of the Change in Water Permeability with ADH 11 Evaluation of the Pf/PDw Ratio 11.1 Large Pore Hypothesis 11.2 Unstirred Layer Effects 12 The Narrow Channel Hypothesis: Single-File Diffusion Through Small Aqueous Channels 13 ADH Increases the Number of Narrow Aqueous Channels in Apical Plasma Membranes 14 The Apparent EA for Water Transport in Cortical Collecting Tubules 14.1 The Raw Data 14.2 Correction for Diffusion Constraints in Series with Apical Membranes 14.3 The “True” EA for Water Transport 15 Pseudo-“Breaks” in EA Measurements 16 Comparison of ADH-Dependent Apical Membrane Water Channels with Gramicidin A Channels 17 Parallel Paths for Water and Solute Permeation 18 Morphologic Studies 19 Intracellular Mediators of ADH Action 19.1 Modulation of ADH Action—α-Adrenergic Agents 19.2 Atrial Natriuretic Peptide 20 Prostaglandins 20.1 Calcium 20.2 Protein Kinase C 21 Summary