title: Volume-dependent regulation of ion carriers in human and rat erythrocytes: role of cytoskeleton and protein phosphorylation.
abstract: This study examines the effect of heat-induced cytoskeleton transitions and phosphoprotein phosphatase inhibitors on the activity of shrinkage-induced Na+, K+, 2Cl- cotransport and Na+/H+ exchange in rat erythrocytes and swelling-induced K+, Cl- cotransport in human and rat blood cells. Preincubation of human and rat erythrocytes at 49 degrees C drastically activated K+, Cl- cotransport and completely (rat) or partly (human) abolished its volume-dependent regulation. The same procedure did not affect basal activity of Na+, K+, 2Cl- cotransport but completely abolished its activation by shrinkage thus suggesting the involvement of a thermosensitive element of cytoskeleton network in the volume-dependent regulation of cotransporters. Both the shrinkage- and electrochemical proton gradient-induced Na+/H+ exchange was inhibited by the heat treatment to the same extent (50-70%), thus indicating the different signaling pathways involved in the activation of Na+, K+, 2Cl- cotransport and Na+/H+ exchange by cell shrinkage. This suggestion is in accordance with data on the different kinetics of volume-dependent activation and inactivation of these carriers as well as on their sensitivity to medium osmolality. Both swelling- and heat-induced increments of K+, Cl- cotransport activity were diminished by inhibitors of phosphoprotein phosphatases (okadaic acid and calyculin). In rat erythrocytes these compounds potentiate shrinkage-induced Na+/H+ exchange. On the contrary, neither basal nor shrinkage-induced Na+, K+, 2Cl- cotransport was affected by these compounds. Our results indicate a key role of cytoskeleton network in volume-dependent activation of K+, Cl- and Na+, K+, 2Cl- cotransport and the involvement of protein phosphorylation-dephosphorylation cycle in regulation of the activity of K+, Cl- cotransport and Na+/H+ exchange.
mesh_terms: D000818:Animals; D002712:Chlorides / Q000378:metabolism; D003599:Cytoskeleton / Q000502:physiology*; D004911:Erythrocyte Volume / Q000502:physiology; D004912:Erythrocytes / Q000166:cytology / Q000201:enzymology / Q000378:metabolism; D006358:Hot Temperature; D006801:Humans; D017136:Ion Transport / Q000502:physiology; D008297:Male; D026901:Membrane Transport Proteins / Q000378:metabolism*; D009994:Osmolar Concentration; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D010766:Phosphorylation; D011188:Potassium / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism; D028021:Sodium-Potassium-Chloride Symporters / Q000378:metabolism; D013045:Species Specificity
chemical_list: D002712:Chlorides; D026901:Membrane Transport Proteins; D017923:Sodium-Hydrogen Exchangers; D028021:Sodium-Potassium-Chloride Symporters; D010749:Phosphoprotein Phosphatases; D011188:Potassium