Volume-sensitive K-Cl cotransport in inside-out vesicles made from erythrocyte membranes from sheep of low-K phenotype.
Unidirectional K ion effluxes were measured from inside-out vesicles prepared from erythrocyte membranes from sheep of the low-K phenotype. Total K efflux was 150 nmol per mg of protein per hr in a Cl medium of 295 mosmol/kg (with the Na/K pump inhibited). Cl-dependent K efflux (determined with methanesulfonate replacing Cl) was 54 nmol/(mg.hr). Cl-dependent K efflux (K-Cl cotransport) increased to 77 nmol/(mg.hr) with osmotic swelling of approximately 30% in 230-mosmol/kg medium and decreased to 13 nmol/(mg.hr) after shrinkage of approximately 60% in 430-mosmol/kg medium. Osmotically induced changes in transport and vesicle volume were reversible. K-Cl cotransport was enhanced by ATP. Nonhydrolyzable ATP analogues failed to substitute for ATP, indicating that phosphorylation is involved. However, in the absence of added ATP there was significant K-Cl cotransport, suggesting that phosphorylation is not essential for function. The results provide clues about the nature of the signals detected by the sensor of cell volume changes and demonstrate that inside-out vesicles from sheep erythrocyte membranes provide an advantageous experimental system for investigation of the volume sensor.
Kracke
G R
GR
Department of Biology, Syracuse University, NY 13244-1220.
Dunham
P B
PB
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002352:Carrier Proteins / Q000097:blood*; D002712:Chlorides / Q000097:blood; D004910:Erythrocyte Membrane / Q000378:metabolism*; D007700:Kinetics; D010641:Phenotype; D011188:Potassium / Q000097:blood*; D012756:Sheep; D027981:Symporters; D000096922:K Cl- Cotransporters
D000255:Adenosine Triphosphate; D002352:Carrier Proteins; D002712:Chlorides; D011188:Potassium; D027981:Symporters; D000096922:K Cl- Cotransporters