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1. Na+/K+/2Cl- co-transport mediates a bidirectional symport of Na+, K+ and Cl-. The important properties of the co-transport system are its requirement for Na+, K+ and Cl- and its inhibition by loop diuretics such as bumetanide. This co-transporter has been described in a number of animal and human tissues. However, its presence in human platelets, although inferred, has not been demonstrated directly. 2. We have studied the efflux of 86Rb+ (a marker for K+) from Rb(+)-loaded platelets, and have defined their response to stimulation by high concentrations of external K+. 3. KCl (30-120 mmol/l) stimulated a concentration-dependent increase in 86Rb+ efflux from the platelets. This efflux was completely inhibited by bumetanide (10 mumol/l) but was insensitive to ouabain and R(+)-[(dihydroindenyl)oxy]alkanoic acid. It also required Cl- in the external medium, but did not depend on the presence of extracellular Na+. 4. These observations suggest that 86Rb+ efflux from platelets stimulated by external K+ occurs via Na+/K+/2Cl- co-transport acting in a K+/K+ (K+/Rb+) exchange mode. 5. Non-stimulated efflux of 86Rb+ from the platelets (i.e. in the presence of 5 mmol/l K+) had the characteristics of Na+/K+/2Cl- co-transport acting in normal mode.

Type

Journal article

Journal

Clin Sci (Lond)

Publication Date

12/1996

Volume

91

Pages

725 - 731

Keywords

Adult, Biological Transport, Blood Platelets, Bumetanide, Carboxylic Acids, Cell Culture Techniques, Chlorine, Humans, Indenes, Ouabain, Potassium, Rubidium Radioisotopes, Sodium