title: Luminal signal in tubuloglomerular feedback: what about potassium?
abstract: Evidence suggests that a minimal luminal [K+] is required to elicit a full tubuloglomerular feedback (TGF) response, consistent with transmission of the TGF signal across the macula densa (MD) via the Na+-2Cl(-)-K+ cotransporter. Furthermore, it appears that luminal [K+] at the MD is close to the K+ affinity of the Na+-2Cl(-)-K+ cotransporter and changes in response to altering late proximal tubular flow rate (VLP), that is, a maneuver that induces a TGF response. These findings suggest that luminal [K+] (besides [Cl-]) could be rate limiting in TGF. In the thick ascending limb of Henle's loop (TALH), most of the luminal K+ is derived from recycling across the apical tubular membrane. Because changing VLP causes relatively greater alterations in the absolute Na+ and Cl- delivery to Henle's loop than in K+ load, the parallel changes of VLP and luminal [K+] at the MD, despite significant alteration in K+-dependent reabsorption of Na+ and Cl- via the Na+-2Cl(-)-K+ cotransporter, imply a transport-dependent adaptation of K+ recycling in TALH.
authors.affiliation: Department of Pharmacology, University of Tübingen, Germany. volker.vallon@uni-tuebingen.de
authors.forename: V
authors.initials: V
authors.lastname: Vallon
authors.forename: H
authors.initials: H
authors.lastname: Osswald
authors.forename: R C
authors.initials: RC
authors.lastname: Blantz
authors.forename: S
authors.initials: S
authors.lastname: Thomson
mesh_terms: D000818:Animals; D005246:Feedback / Q000502:physiology*; D006801:Humans; D007678:Kidney Glomerulus / Q000502:physiology*; D007684:Kidney Tubules / Q000502:physiology*; D011188:Potassium / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D011188:Potassium