ISSN:
1432-1424
Keywords:
K+ fluxes
;
MDCK
;
ouabain
;
furosemide
;
cultured epithelium
;
Na++K++Cl− cotransport
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Summary Bidirectional transepithelial K+ flux measurements across ‘high-resistance’ epithelial monolayers of MDCK cells grown upon millipore filters show no significant net K+ flux. Measurements of influx and efflux across the basal-lateral and apical cell membranes demonstrate that the apical membranes are effectively impermeable to K+. K+ influx across the basal-lateral cell membranes consists of an ouabain-sensitive component, an ouabain-insensitive component, an ouabain-insensitive but furosemide-sensitive component, and an ouabain-and furosemide-insensitive component. The action of furosemide upon K+ influx is independent of (Na+−K+)-pump inhibition. The furosemide-sensitive component is markedly dependent upon the medium K+, Na+ and Cl− content. Acetate and nitrate are ineffective substitutes for Cl−, whereas Br− is partially effective. Partial Cl− replacement by NO3 gives a roughly linear increase in the furosemide-sensitive component. Na+ replacement by choline abolishes the furosemide-sensitive component, whereas Li+ is a partially effective replacement. Partial Na+ replacement with choline gives an apparent affinity of ∼7mm Na, whereas variation of the external K+ content gives an affinity of the furosemide-sensitive component of 1.0mm. Furosemide inhibition is of high affinity (K 1/2=3 μm). Piretanide, ethacrynic acid, and phloretin inhibit the same component of passive K+ influx as furosemide; amiloride, 4,-aminopyridine, and 2,4,6-triaminopyrimidine partially so. SITS was ineffective. Externally applied furosemide and Cl− replacement by NO 3 − inhibit K+ efflux across the basal-lateral membranes indicating that the furosemide-sensitive component consists primarily of K∶K exchange.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01870473
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