期刊
AMERICAN JOURNAL OF PHYSIOLOGY-CELL PHYSIOLOGY
卷 278, 期 5, 页码 C965-C972出版社
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/ajpcell.2000.278.5.C965
关键词
calcium ion; red blood cell; calcium ion adenosinetriphosphatase; membrane potential
资金
- NHLBI NIH HHS [HL-07094] Funding Source: Medline
- NIDDK NIH HHS [DK-37512] Funding Source: Medline
The plasma membrane Ca2+ pump is known to mediate Ca2+/H+ exchange. Extracellular protons activated Ca-45(2+) efflux from human red blood cells with a half-maximal inhibition constant of 2 nM when the intracellular pH was fixed. An increase in pH from 7.2 to 8.2 decreased the IC50 for extracellular Ca2+ from similar to 33 to similar to 6 mM. Changing the membrane potential by >54 mV had no effect on the IC50 for extracellular Ca2+. This argues against Ca2+ release through a high-field access channel. Extracellular Ni2+ inhibited Ca2+ efflux with an IC50 Of 11 mM. Extracellular Cd2+ inhibited with an IC50 of 1.5 mM, >10 times better than Ca2+. The Cd2+ IC50 also decreased when the pH was raised from 7.1 to 8.2, consistent with Ca2+, Cd2+, and Hi competing for the same site. The higher affinity for inhibition by Ni2+ and Cd2+ is consistent with a histidine or cysteine as part of the release site. The cysteine reagent 2-(trimethylammonium)ethyl methanethiosulfonate did not inhibit Ca2+ efflux. Our results are consistent with the notion that the release site contains a histidine.
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