title: Effects of barium ions on tubuloglomerular feedback.
abstract: The furosemide sensitivity of the tubuloglomerular feedback (TGF) response has suggested an important role for the Na-2Cl-K cotransporter in the mechanism by which increased luminal NaCl concentration causes afferent arteriolar vasoconstriction. The present experiments in anesthetized rats were performed to evaluate the effect of K channel blockade with Ba on TGF, since Ba has been shown to inhibit NaCl transport in the thick ascending limb. The presence of either 1.5 or 2 mM BaCl2 during retrograde perfusion with a 135 mM NaCl solution reduced the decrease of early proximal flow rate (VEP) by 2.7 +/- 0.76 (P < 0.02) and 4.2 +/- 0.8 nl/min (P < 0.01) compared with perfusion without BaCl2. Retrograde perfusion with 38 mM NaCl + 5 mM KCl reduced VEP by 10.4 +/- 1.3 nl/min, whereas 40 mM NaCl + 1.5 mM BaCl2 caused a reduction by only 6.1 +/- 1.4 nl/min (P < 0.001). In contrast to the inhibition caused by retrograde perfusion with low concentrations of BaCl2, increased vasoconstriction was seen during retrograde perfusion with 5 mM BaCl2 or during orthograde perfusion with 10 mM BaCl2. The addition of 10(-4) M furosemide to a solution containing 5 mM BaCl2 largely blocked the increased vasoconstrictor response. Peritubular perfusion with a solution containing 5 mM BaCl2 caused a fall in stop-flow pressure in an adjacent nephron by 10.7 +/- 1.5 mmHg (P < 0.001). These results indicate that under our experimental conditions Ba ions exert a dual effect on vascular responses to changes in luminal NaCl concentration.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Physiology, University of Michigan, Ann Arbor 48104, USA.
authors.forename: J
authors.initials: J
authors.lastname: Schnermann
mesh_terms: D000818:Animals; D001464:Barium / Q000494:pharmacology*; D005246:Feedback; D005665:Furosemide / Q000494:pharmacology; D007477:Ions; D007678:Kidney Glomerulus / Q000502:physiology*; D007684:Kidney Tubules / Q000502:physiology*; D008297:Male; D009994:Osmolar Concentration; D010477:Perfusion; D026902:Potassium Channel Blockers; D051381:Rats; D017207:Rats, Sprague-Dawley; D015291:Transforming Growth Factors / Q000378:metabolism
chemical_list: D007477:Ions; D026902:Potassium Channel Blockers; D001464:Barium; D015291:Transforming Growth Factors; D005665:Furosemide