A Ca-dependent K channel in «luminal» membranes from the renal outer medulla

This paper describes properties of 86Rb fluxes through K channels in "luminal" membrane vesicles prepared from rabbit renal outer medulla. By measuring 86Rb uptake against an opposing chemical gradient of K ions, using membranes loaded with KCl, a transient accumulation of isotope is obser...

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Bibliographic Details
Published in:The Journal of membrane biology 1986-01, Vol.93 (2), p.177-186
Main Authors: BURNHAM, C, BRAW, R, KARLISH, S. J. D
Format: Article
Language:English
Subjects:
Animals
Barium - pharmacology
Biological and medical sciences
calcium
Calcium - pharmacology
Fundamental and applied biological sciences. Psychology
Intracellular Membranes - physiology
Ion Channels - drug effects
Ion Channels - physiology
kidney
Kidney Medulla - physiology
Kinetics
Microsomes - physiology
potassium
Potassium - metabolism
Rabbits
Rubidium - metabolism
Vertebrates: urinary system
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Summary:This paper describes properties of 86Rb fluxes through K channels in "luminal" membrane vesicles prepared from rabbit renal outer medulla. By measuring 86Rb uptake against an opposing chemical gradient of K ions, using membranes loaded with KCl, a transient accumulation of isotope is observed, which is blocked by Ba ions. This is the behavior expected of a conductive Rb flux through a Ba-sensitive K channel. The 86Rb accumulation is driven by an electrical diffusion potential as shown in experiments using either vesicles loaded with different anions, or an outwardly directed Li gradient with a Li ionophore. The vesicles containing the channel show a cation selectivity with the order Rb greater than K greater than Cs greater than Li greater than Na greater than choline. The Ba-sensitive Rb flux is dependent on Ca within the vesicles, with a very high affinity estimated as K0.5 10 to 100 nM. The vesicles appear to be right-side-out. The Ba-sensitive 86Rb uptake is also inhibited by quinine K0.5 30 microM but is insensitive to tetraethyl ammonium ions and apamin. These isotope flux experiments complement electrophysiological experiments in providing independent evidence for the existence of K channels in the luminal surface of cells of this ascending limb of the loop of Henle. The very high Ca affinity suggests that cytoplasmic Ca could play an important role in regulation of transepithelial salt flux in this region of the nephron.
ISSN:0022-2631
1432-1424
DOI:10.1007/BF01870809