J. Biol. Chem., Vol. 266, Issue 34, 22975-22982, Dec, 1991

Regulation of free cytosolic Ca2+ concentration in the outer segments of bovine retinal rods by Na-Ca-K exchange measured with fluo-3. I. Efficiency of transport and interactions between cations

PP Schnetkamp, XB Li, DK Basu and RT Szerencsei
Department of Medical Biochemistry, University of Calgary, Alberta, Canada.

Regulation of free cytosolic Ca2+ concentration in the rod outer segments (ROS) isolated from bovine retinas was examined with the fluorescent Ca(2+)-indicating dye fluo-3. In situ calibration of cytosolic fluo-3 was done in the presence of the Ca2+ ionophore A23187 and yielded a dissociation constant of 500 nM for the Ca(2+)-fluo-3 complex. Ca2+ influx in Ca(2+)-depleted ROS was completely abolished when internal Na+ was removed suggesting that Ca2+ influx exclusively occurred via Na-Ca-K exchange. The most striking observation was that Na-Ca-K exchange could mediate a rapid increase in cytosolic free Ca2+ over the most of the usable indicating range of fluo-3 (from 10 nM to 2 microM), even when exposed to free external Ca2+ concentrations as low as 10 nM. From a comparison between changes in free Ca2+ and changes in total Ca2+, we conclude that physiologically occurring changes in cytosolic free Ca2+ are mediated by exchange fluxes less than 1% of the maximal Na-Ca-K exchange flux. The Na-Ca-K exchanger could mediate both K(+)-dependent and K(+)-independent Ca2+ influx; Li+ caused a complete inhibition of K(+)-independent Ca2+ influx, but had no effect on K(+)- dependent Ca2+ influx. We examined the complex interactions of alkali cations with Ca2+ influx and discuss the results in terms of a three- site model for the Na-Ca-K exchanger (Schnetkamp, P. P. M. and Szerencsei, R. T. (1991) J. Biol. Chem. 266, 189-197). Ca2+ competed with one Mg2+ ion or two Na+ ions for binding to a common site. High K+ concentration greatly diminished the ability of Na+ and Mg2+ to compete with Ca2+ for this common site on the exchanger protein. As a result, high internal K+ induced a conformation of the exchange protein that kinetically favoured Ca2+ extrusion.
CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				Y. SHIBUKAWA, K. J. KANG, T. G. KINJO, R. T. SZERENCSEI, H. F. ALTIMIMI, P. PRATIKHYA, R. J. WINKFEIN, and P. P. M. SCHNETKAMP Structure-Function Relationships of the NCKX2 Na+/Ca2+-K+ Exchanger Ann. N.Y. Acad. Sci., March 1, 2007; 1099(1): 16 - 28. [Abstract] [Full Text] [PDF]

				F. Visser, V. Valsecchi, L. Annunziato, and J. Lytton Analysis of Ion Interactions with the K+ -dependent Na+/Ca+ Exchangers NCKX2, NCKX3, and NCKX4: IDENTIFICATION OF THR-551 AS A KEY RESIDUE IN DEFINING THE APPARENT K+ AFFINITY OF NCKX2 J. Biol. Chem., February 16, 2007; 282(7): 4453 - 4462. [Abstract] [Full Text] [PDF]

				H. F. Altimimi and P. P. M. Schnetkamp Na+-dependent Inactivation of the Retinal Cone/Brain Na+/Ca2+-K+ Exchanger NCKX2 J. Biol. Chem., February 9, 2007; 282(6): 3720 - 3729. [Abstract] [Full Text] [PDF]

				K.-J. Kang, T. G. Kinjo, R. T. Szerencsei, and P. P. M. Schnetkamp Residues Contributing to the Ca2+ and K+ Binding Pocket of the NCKX2 Na+/Ca2+-K+ Exchanger J. Biol. Chem., February 25, 2005; 280(8): 6823 - 6833. [Abstract] [Full Text] [PDF]

				K.-J. Kang, Y. Shibukawa, R. T. Szerencsei, and P. P. M. Schnetkamp Substitution of a Single Residue, Asp575, Renders the NCKX2 K+-dependent Na+/Ca2+ Exchanger Independent of K+ J. Biol. Chem., February 25, 2005; 280(8): 6834 - 6839. [Abstract] [Full Text] [PDF]

				R. T. SZERENCSEI, R. J. WINKFEIN, C. B. COOPER, C. PRINSEN, T. G. KINJO, K. KANG, and P. P.M. SCHNETKAMP The Na/Ca-K Exchanger Gene Family Ann. N.Y. Acad. Sci., November 1, 2002; 976(1): 41 - 52. [Abstract] [Full Text] [PDF]

				R. WEBEL, K. HAUG-COLLET, B. PEARSON, R. T. SZERENCSEI, R. J. WINKFEIN, P. P.M. SCHNETKAMP, and N. J. COLLEY Potassium-Dependent Sodium-Calcium Exchange through the Eye of the Fly Ann. N.Y. Acad. Sci., November 1, 2002; 976(1): 300 - 314. [Abstract] [Full Text] [PDF]

				J. LYTTON, X.-F. LI, H. DONG, and A. KRAEV K+-Dependent Na+/Ca2+ Exchangers in the Brain Ann. N.Y. Acad. Sci., November 1, 2002; 976(1): 382 - 393. [Abstract] [Full Text] [PDF]

				C. F. M. Prinsen, R. T. Szerencsei, and P. P. M. Schnetkamp Molecular Cloning and Functional Expression of the Potassium-Dependent Sodium-Calcium Exchanger from Human and Chicken Retinal Cone Photoreceptors J. Neurosci., February 15, 2000; 20(4): 1424 - 1434. [Abstract] [Full Text] [PDF]

				R. T. Szerencsei, J. E. Tucker, C. B. Cooper, R. J. Winkfein, P. J. Farrell, K. Iatrou, and P. P. M. Schnetkamp Minimal Domain Requirement for Cation Transport by the Potassium-dependent Na/Ca-K Exchanger. COMPARISON WITH AN NCKX PARALOG FROM CAENORHABDITIS ELEGANS J. Biol. Chem., January 7, 2000; 275(1): 669 - 676. [Abstract] [Full Text] [PDF]

				K. Haug-Collet, B. Pearson, R. Webel, R.T. Szerencsei, R.J. Winkfein, P.P.M. Schnetkamp, and N.J. Colley Cloning and Characterization of a Potassium-dependent Sodium/Calcium Exchanger in Drosophila J. Cell Biol., November 1, 1999; 147(3): 659 - 670. [Abstract] [Full Text] [PDF]

				M. Kimura, E. M. Jeanclos, R. J. Donnelly, J. Lytton, J. P. Reeves, and A. Aviv Physiological and molecular characterization of the Na+/Ca2+ exchanger in human platelets Am J Physiol Heart Circ Physiol, September 1, 1999; 277(3): H911 - H917. [Abstract] [Full Text] [PDF]

				P. P. M. Schnetkamp and P. P. Schnetkamp How Does the Retinal Rod Na-Ca+K Exchanger Regulate Cytosolic Free Ca[IMAGE]? J. Biol. Chem., June 2, 1995; 270(22): 13231 - 13239. [Abstract] [Full Text] [PDF]

				A. Kraev, B. D. Quednau, S. Leach, X.-F. Li, H. Dong, R. Winkfein, M. Perizzolo, X. Cai, R. Yang, K. D. Philipson, et al. Molecular Cloning of a Third Member of the Potassium-dependent Sodium-Calcium Exchanger Gene Family, NCKX3 J. Biol. Chem., June 15, 2001; 276(25): 23161 - 23172. [Abstract] [Full Text] [PDF]

				H. Dong, P. E. Light, R. J. French, and J. Lytton Electrophysiological Characterization and Ionic Stoichiometry of the Rat Brain K+-dependent Na+/Ca2+ Exchanger, NCKX2 J. Biol. Chem., July 6, 2001; 276(28): 25919 - 25928. [Abstract] [Full Text] [PDF]