How does the retinal rod Na-Ca+K exchanger regulate cytosolic free Ca2+?

The Journal of Biological Chemistry
P P Schnetkamp

Abstract

The roles of 1) inactivation of Na-Ca+K exchange and 2) Ca2+ release from discs in regulation of cytosolic free Ca2+ were examined in intact rod outer segments (ROS) purified from bovine retinas. Measurements of cytosolic free Ca2+ (with fluo-3) were combined with Ca2+ flux measurements (45Ca) in ROS that contained about 600 microM total Ca2+. Na(+)-induced Ca2+ extrusion was measured in a Ca(2+)-free medium and did not lower cytosolic free Ca2+ to below 1 nM as expected from a coupling stoichiometry of 4Na+:(1Ca(2+) + 1K+). Instead, cytosolic free Ca2+ was rapidly (20 s) lowered from about 1300 nM to 100-150 nM, while at the same time about 35% of total ROS Ca2+ was removed. During the next 40 min cytosolic free Ca2+ remained virtually steady, but total ROS Ca2+ was reduced by a further 50% at a 100-fold lower rate than that observed for the initial fast phase. The steady cytosolic Ca2+ concentration resulted from Ca2+ release from discs and subsequent removal across the plasma membrane by Na-Ca+K exchange operating at a greatly reduced rate. Addition of the alkali cation channel ionophore gramicidin led to a persistent increase in cytosolic free Ca2+ concentration to about 400 nM, presumably caused by an increase in intracell...Continue Reading

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Citations

Nov 1, 1996·Journal of Bone and Mineral Research : the Official Journal of the American Society for Bone and Mineral Research·K E WhiteP A Friedman
Oct 6, 2007·Molecular Neurobiology·Rosa Gomez-VillafuertesJose R Naranjo
Apr 17, 1999·Journal of Photochemistry and Photobiology. B, Biology·I M Pepe
Oct 6, 2001·Progress in Retinal and Eye Research·I M Pepe
Aug 6, 2002·Frontiers in Bioscience : a Journal and Virtual Library·David Krizaj, David R Copenhagen
Apr 18, 2001·The Journal of Physiology·H R Matthews, G L Fain
Apr 15, 1996·Annals of the New York Academy of Sciences·P P SchnetkampR T Szerencsei
Oct 1, 1995·Cell Calcium·P P Schnetkamp
Nov 20, 2003·The Journal of Biological Chemistry·Xinjiang Cai, Jonathan Lytton
Oct 16, 2002·The Journal of Biological Chemistry·Xinjiang CaiJonathan Lytton
Jan 12, 2001·Physiological Reviews·G L FainY Koutalos
Feb 7, 2001·American Journal of Physiology. Cell Physiology·S PoonJ Lytton
Dec 28, 2002·Annals of the New York Academy of Sciences·D H SchulzeF L Margolis
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Dec 14, 2006·The Journal of Biological Chemistry·Haider F Altimimi, Paul P M Schnetkamp
Apr 18, 2021·Pflügers Archiv : European journal of physiology·Soumyaparna DasFrançois Paquet-Durand

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