Cold activation of Na influx through the Na-H exchange pathway in guinea pig red cells.
Previous work showed that amiloride partially inhibits the net gain of Na in cold-stored red cells of guinea pig and that the proportion of unidirectional Na influx sensitive to amiloride increases dramatically with cooling. This study shows that at 37 degrees C amiloride-sensitive (AS) Na influx in guinea pig red blood cells is activated by cytoplasmic H+, hypertonic incubation, phorbol ester in the presence of extracellular Ca2+ and is correlated with cation-dependent H+ loss from acidified cells. Cytoplasmic acidification increases AS Na efflux into Na-free medium. These properties are consistent with the presence of a Na-H exchanger with a H+ regulatory site. Elevation of cytoplasmic free Mg2+ above 3 mM greatly increases AS Na influx: this correlates with a Na-dependent loss of Mg2+, indicating the presence of a Na-Mg exchanger. At 20 degrees C activators of Na-H exchange have little or no further stimulatory effect on the already elevated AS Na influx. AS Na influx is much larger than either Na-dependent H+ loss or AS Na efflux at 20 degrees C. The affinity of the AS Na influx for cytoplasmic H+ is greater at 20 degrees C than at 37 degrees C. Depletion of cytoplasmic Mg2+ does not abolish the high AS Na influx at 20 degrees C. Thus, elevation of AS Na influx with cooling appears to be due to increased activity of a Na-H exchanger (operating in a "slippage" mode) caused by greater sensitivity to H+ at a regulatory site.
Department of Physiology and Biophysics, University of Illinois, Urbana 61801.
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D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002352:Carrier Proteins / Q000097:blood; D003080:Cold Temperature; D004912:Erythrocytes / Q000187:drug effects / Q000378:metabolism*; D006168:Guinea Pigs; D006982:Hypertonic Solutions; D066298:In Vitro Techniques; D017136:Ion Transport / Q000187:drug effects; D008274:Magnesium / Q000097:blood; D011522:Protons; D012964:Sodium / Q000097:blood*; D017923:Sodium-Hydrogen Exchangers; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D002352:Carrier Proteins; D006982:Hypertonic Solutions; D011522:Protons; D017923:Sodium-Hydrogen Exchangers; D000584:Amiloride; D012964:Sodium; D008274:Magnesium; D013755:Tetradecanoylphorbol Acetate