Temperature effects on ion transport across the erythrocyte membrane of the frog Rana temporaria.
Unidirectional K+ and Na+ influxes in the frog erythrocytes incubated in Cl- or NO(3)- media with 2.7 mM K+ were measured using 86Rb and 22Na as tracers. K+ influx was inhibited by 35-55% in the presence of 0.2-1.0 mM furosemide but it was unaffected by 0.1-0.2 mM bumetanide. Furosemide at a concentration of 0.5 mM had no effect on K+ loss from the frog red cells incubated in a nominally K(+)-free medium. Together with our previous studies the data support the existence of K-Cl cotransport and the absence of Na-K-2Cl cotransport in the frog erythrocyte membrane. Cell cooling from 20 to 5 degrees C caused a decrease in K+ influx and K+ efflux via the K-Cl cotransporter (3.2- and 3.7-fold, respectively) giving an apparent energy of activation (EA) of about 60 kJ/mol and Q10 value of 2.5. Only small decline (approximately 30%) in the ouabain-sensitive K+ influx was found as temperature was changed from 20 to 5-10 degrees C. Low values of Q10 (approximately 1.5) and EA (27.3 kJ/mol) were obtained for passive K+ influx in the frog erythrocytes (ouabain-insensitive in NO(3)- medium) at temperature within 5-20 degrees C. However, the temperature coefficients were greater for passive Na+ influx and passive K+ efflux (Q10 approximately 2.4-2.5 and EA approximately 56-58 kJ/mol). The temperature dependence of all ion transport components displayed discontinuities showing no changes at temperature between 5 and 10 degrees C. Thus, cooling of the frog red cells is associated with a greater decrease of Na+ influx and K+ efflux than passive and active K+ influx. These data indicate that the preservation of a relative high activity of the Na,K-pump during cell cooling and also the temperature-induced changes in the K-Cl cotransport activity and ion passive diffusion contribute to maintenance of ion concentration gradients in the frog erythrocytes at decreased temperature.
Agalakova
N I
NI
Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St Petersburg.
Lapin
A V
AV
Gusev
G P
GP
D000818:Animals; D002034:Bumetanide / Q000494:pharmacology; D002352:Carrier Proteins / Q000097:blood; D002712:Chlorides / Q000097:blood; D004910:Erythrocyte Membrane / Q000187:drug effects / Q000378:metabolism*; D005665:Furosemide / Q000494:pharmacology; D066298:In Vitro Techniques; D017136:Ion Transport / Q000187:drug effects; D007700:Kinetics; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000097:blood; D011896:Rana temporaria / Q000097:blood*; D012964:Sodium / Q000097:blood; D027981:Symporters; D013696:Temperature; D000096922:K Cl- Cotransporters
D002034:Bumetanide; D002352:Carrier Proteins; D002712:Chlorides; D005665:Furosemide; D010042:Ouabain; D011188:Potassium; D012964:Sodium; D027981:Symporters; D000096922:K Cl- Cotransporters