title: Effects of the potassium channel blocker barium on sodium and potassium transport in the rat loop of Henle in vivo.
abstract: In vitro evidence suggests that the 'recycling' of K(+) ions through luminal K(+) channels in the thick ascending limb of the loop of Henle (TALH) is essential for the normal operation of the luminal Na(+)-K(+)-2Cl(-) co-transporter. In the present study these channels were investigated in vivo by perfusing superficial loops of Henle in anaesthetised rats with and without the K(+) channel blocker barium. Using a standard perfusate, intraluminal barium (5 mmol l(-1)) reduced sodium reabsorption (J(Na)) from 1887 +/- 50 to 1319 +/- 53 pmol min(-1) (P < 0.001). When the experiment was repeated using a low-Na(+) perfusate, designed to inhibit reabsorption in the pars recta (the initial segment of the loop of Henle), a similar reduction in J(Na) was observed (from 698 +/- 47 to 149 +/- 23 pmol min(-1), P < 0.001), strongly suggesting that the effect of barium is localised to the TALH. The magnitude of the reduction in J(Na) during blockade of K(+) channels confirms the importance of K(+) recycling in facilitating Na(+) reabsorption in the TALH in vivo. However, the reduction in J(Na) was not associated with a fall in the K(+) concentration of the fluid collected at the early distal tubule. When bumetanide, an inhibitor of the Na(+)-K(+)-2Cl(-) co-transporter, was included in the low-Na(+) perfusate, net K(+) secretion was observed. Addition of barium to this perfusate reduced, but did not abolish, the secretion, suggesting that bumetanide-induced K(+) secretion results partly from paracellular transport. Experimental Physiology (2001) 86.4, 469-474.
authors.affiliation: Division of Biomedical Sciences, Imperial College School of Medicine, London SW7 2AZ, UK. s.walter@ic.ac.uk
authors.forename: S J
authors.initials: SJ
authors.lastname: Walter
authors.forename: D G
authors.initials: DG
authors.lastname: Shirley
authors.forename: E J
authors.initials: EJ
authors.lastname: Folkerd
authors.forename: R J
authors.initials: RJ
authors.lastname: Unwin
mesh_terms: D000818:Animals; D001464:Barium / Q000494:pharmacology*; D001794:Blood Pressure; D002034:Bumetanide / Q000494:pharmacology; D004232:Diuretics / Q000494:pharmacology; D008138:Loop of Henle / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D010477:Perfusion; D011188:Potassium / Q000493:pharmacokinetics*; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000493:pharmacokinetics*; D014867:Water / Q000378:metabolism
chemical_list: D004232:Diuretics; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D014867:Water; D002034:Bumetanide; D001464:Barium; D012964:Sodium; D011188:Potassium