Cation transport and cell volume changes in maturing rat reticulocytes.
During maturation, reticulocytes lose membrane material, including transporters, and this is accompanied by a loss of cell water and volume. Here we determined a possible role of ion transport in adjusting cell volume during maturation. Reticulocytes and red blood cells of different ages were prepared from erythropoietin-treated rats by density gradient fractionation. Cell volume and ion transport were measured in freshly prepared cells and in reticulocytes during in vitro maturation. Reticulocytes had an increased K content and cell volume, whereas intracellular Na was decreased. All parameters approached whole blood values after 2 days in culture. Na-K pump was elevated in reticulocytes and decreased during maturation. Na-K-2Cl cotransport (NKCC) activity was lower in reticulocytes and was activated 8- and 20-fold by shrinkage and okadaic acid, respectively, whereas stimulation was barely detectable in high-buoyant density red blood cells. The ouabain- and bumetanide-insensitive Na flux in reticulocytes decreased on maturation. Most of it was inhibited by amiloride, indicating the presence of Na/proton exchange. Our results show that, although the Na-K-pump activity in reticulocytes is very much increased, the enhanced capacity of NKCC is essentially cryptic until stimulated. Both types of capacities (activities) decrease during maturation, indicating a possible loss of transport protein. The decrease was constrained to the period of reticulocyte maturation. Loss of transport capacity appears to exceed the loss of membrane surface area. Reticulocyte age-related changes in the net electrochemical driving force indicate that the increasing NKCC activity might contribute to the reduction in cell water.
Mairbäurl
H
H
Department of Sports Medicine, University of Heidelberg, 69115 Heidelberg, Germany. heimo_mairbaeurl@med.uni-heidelberg.de
Schulz
S
S
Hoffman
J F
JF
D000818:Animals; D001692:Biological Transport / Q000502:physiology; D001834:Body Water / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D002412:Cations / Q000378:metabolism*; D016922:Cellular Senescence / Q000502:physiology; D004912:Erythrocytes / Q000378:metabolism / Q000502:physiology; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D012156:Reticulocytes / Q000166:cytology* / Q000378:metabolism / Q000502:physiology*; D028021:Sodium-Potassium-Chloride Symporters; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
D002352:Carrier Proteins; D002412:Cations; D028021:Sodium-Potassium-Chloride Symporters; D000254:Sodium-Potassium-Exchanging ATPase