Evidence for an R(+)-[(dihydroindenyl)oxy]alkanoic acid-sensitive K+/Cl- co-transporter in human platelets and its interaction with the Na+/K+/2Cl- co-transporter.
1. The K+/Cl- co-transport system is activated by a number of interventions, such as cell swelling and stimulation with N-ethylmaleimide. It is specifically inhibited by R(+)-[(dihydroindenyl)oxy]alkanoic acid and requires the presence of K+ and Cl- on the same side of the cell membrane. This co-transporter has been studied extensively, mainly in erythrocytes of many species, in which it plays a key role in cell volume regulation. Here we present evidence that human platelets contain K+/Cl- co-transporters. 2. We have studied the efflux of 86Rb+ (a marker for K+) from 86Rb(+)-loaded human platelets, and have defined their response to stimulation by N-ethylmaleimide. 3. N-Ethylmaleimide (0.5 and 1 mmol/l) stimulated an increase in cumulative 86Rb+ efflux in a concentration-dependent manner. This efflux was inhibited by R(+)-[(dihydroindenyl)oxy]alkanoic acid (10 mumol/l) but was insensitive to bumetanide. It also required the presence of external Cl-. 4. These observations suggest that 86Rb+ efflux from the platelets stimulated by N-ethylmaleimide occurs via K+/Cl- co-transport. 5. When the K+/Cl- co-transporter was stimulated by N-ethylmaleimide we were unable to stimulate the Na+/K+/2Cl- co-transporter with a high external concentration of KCl or inhibit 86Rb+ efflux with bumetanide. Together with other evidence, this suggests that when the K+/Cl- co-transporter is stimulated with N-ethylmaleimide, the Na+/K+/2Cl- co-transporter is inhibited.
de Silva
H A
HA
University Department of Clinical Pharmacology, Radcliffe Infirmary, Oxford, U.K.
Aronson
J K
JK
D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D002034:Bumetanide / Q000494:pharmacology; D002264:Carboxylic Acids / Q000494:pharmacology; D002352:Carrier Proteins / Q000187:drug effects* / Q000378:metabolism*; D004232:Diuretics / Q000494:pharmacology; D005033:Ethylmaleimide / Q000494:pharmacology; D006801:Humans; D007192:Indenes / Q000494:pharmacology; D012414:Rubidium Radioisotopes / Q000378:metabolism; D028021:Sodium-Potassium-Chloride Symporters; D013268:Stimulation, Chemical; D013439:Sulfhydryl Reagents / Q000494:pharmacology; D027981:Symporters; D000096922:K Cl- Cotransporters
D002034:Bumetanide; D002264:Carboxylic Acids; D002352:Carrier Proteins; D004232:Diuretics; D005033:Ethylmaleimide; D007192:Indenes; D012414:Rubidium Radioisotopes; D028021:Sodium-Potassium-Chloride Symporters; D013439:Sulfhydryl Reagents; D027981:Symporters; D000096922:K Cl- Cotransporters; C059990:((dihydroindenyl)oxy)alkanoic acid