A Na+- and Cl- -activated K+ channel in the thick ascending limb of mouse kidney.
This study investigates the presence and properties of Na+-activated K+ (K(Na)) channels in epithelial renal cells. Using real-time PCR on mouse microdissected nephron segments, we show that Slo2.2 mRNA, which encodes for the K(Na) channels of excitable cells, is expressed in the medullary and cortical thick ascending limbs of Henle's loop, but not in the other parts of the nephron. Patch-clamp analysis revealed the presence of a high conductance K+ channel in the basolateral membrane of both the medullary and cortical thick ascending limbs. This channel was highly K+ selective (P(K)/P(Na) approximately 20), its conductance ranged from 140 to 180 pS with subconductance levels, and its current/voltage relationship displayed intermediate, Na+-dependent, inward rectification. Internal Na+ and Cl- activated the channel with 50% effective concentrations (EC50) and Hill coefficients (nH) of 30 +/- 1 mM and 3.9 +/- 0.5 for internal Na+, and 35 +/- 10 mM and 1.3 +/- 0.25 for internal Cl-. Channel activity was unaltered by internal ATP (2 mM) and by internal pH, but clearly decreased when internal free Ca2+ concentration increased. This is the first demonstration of the presence in the epithelial cell membrane of a functional, Na+-activated, large-conductance K+ channel that closely resembles native K(Na) channels of excitable cells. This Slo2.2 type, Na+- and Cl--activated K+ channel is primarily located in the thick ascending limb, a major renal site of transcellular NaCl reabsorption.
Paulais
Marc
M
UPMC, CNRS UMR7134, Institut Fédératif de Recherches 58, Paris, France. Marc.Paulais@bhdc.jussieu.fr
Lachheb
Sahran
S
Teulon
Jacques
J
D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D002462:Cell Membrane / Q000737:chemistry / Q000502:physiology; D002712:Chlorides / Q000502:physiology; D004847:Epithelial Cells / Q000737:chemistry / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000032:analysis / Q000737:chemistry / Q000502:physiology; D008138:Loop of Henle / Q000737:chemistry* / Q000166:cytology / Q000502:physiology; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D009419:Nerve Tissue Proteins; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000032:analysis* / Q000235:genetics / Q000502:physiology*; D000081033:Potassium Channels, Sodium-Activated; D012333:RNA, Messenger / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012964:Sodium / Q000502:physiology; D019459:Urothelium / Q000737:chemistry* / Q000502:physiology
D002712:Chlorides; D051036:Large-Conductance Calcium-Activated Potassium Channels; D009419:Nerve Tissue Proteins; D015221:Potassium Channels; D000081033:Potassium Channels, Sodium-Activated; D012333:RNA, Messenger; C479624:Slo2 protein, mouse; D000255:Adenosine Triphosphate; D012964:Sodium