title: Transepithelial electrochemical gradients in the proximal convoluted tubule during potassium depletion in the rat.
abstract: 1. In order to examine the electrochemical gradient for potassium reabsorption across the S2 segment of the proximal convoluted tubule, transepithelial potential differences and transepithelial potassium concentrations were measured in anaesthetized potassium-replete and potassium-depleted rats. 2. Potassium-depleted rats were markedly hypokalaemic (plasma potassium, 1.4 +/- 0.1 vs. 4.1 +/- 0.1 mmol l-1 in potassium-replete rats) and had a significantly reduced muscle potassium content. In confirmation of previous reports, glomerular filtration rate was slightly reduced, while fractional reabsorption in the proximal convoluted tubule was enhanced. 3. In potassium-replete animals, the transepithelial potential difference (PD) at the late proximal convoluted tubule was +2.1 +/- 0.3 mV (lumen positive) and the tubular fluid to plasma ultrafiltrate concentration ratio for potassium (TFK/UFK) at the same site was 1. 03 +/- 0.01. In potassium-depleted rats, there was a striking reversal of the transepithelial PD (to -4.0 +/- 0.4 mV), while the TFK/UFK was increased to 1.19 +/- 0.03. 4. The data from both potassium-replete and potassium-depleted animals are consistent with accumulating evidence that potassium reabsorption in the proximal convoluted tubule is passive in nature and depends partly on diffusion down an electrochemical gradient.
authors.affiliation: Division of Biomedical Sciences, Imperial College School of Medicine, Charing Cross Hospital, London W6 8RF, UK.d.shirley@cxwms.ac.uk
authors.forename: D G
authors.initials: DG
authors.lastname: Shirley
authors.forename: S J
authors.initials: SJ
authors.lastname: Walter
authors.forename: E J
authors.initials: EJ
authors.lastname: Folkerd
authors.forename: R J
authors.initials: RJ
authors.lastname: Unwin
authors.forename: M A
authors.initials: MA
authors.lastname: Bailey
mesh_terms: D000042:Absorption; D000818:Animals; D001826:Body Fluids / Q000378:metabolism; D004563:Electrochemistry; D004594:Electrophysiology; D004848:Epithelium / Q000378:metabolism / Q000502:physiology; D005919:Glomerular Filtration Rate / Q000502:physiology; D007008:Hypokalemia / Q000097:blood; D007687:Kidney Tubules, Proximal / Q000378:metabolism* / Q000502:physiology; D008297:Male; D011188:Potassium / Q000097:blood / Q000378:metabolism; D011191:Potassium Deficiency / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D011188:Potassium