Voltage and Ca(2+) dependence of pre-steady-state currents of the Na-Ca exchanger generated by Ca(2+) concentration jumps

Biophysical Journal
M KapplKlaus Hartung

Abstract

The Ca(2+) concentration and voltage dependence of the relaxation kinetics of the Na-Ca exchanger after a Ca(2+) concentration jump was measured in excised giant membrane patches from guinea pig heart. Ca(2+) concentration jumps on the cytoplasmic side were achieved by laser flash-induced photolysis of DM-nitrophen. In the Ca-Ca exchange mode a transient inward current is generated. The amplitude and the decay rate of the current saturate at concentrations >10 microM. The integrated current signal, i.e., the charge moved is fairly independent of the amount of Ca(2+) released. The amount of charge translocated increases at negative membrane potentials, whereas the decay rate constant shows no voltage dependence. It is suggested that Ca(2+) translocation occurs in at least four steps: intra- and extracellular Ca(2+) binding and two intramolecular transport steps. Saturation of the amplitude and of the relaxation of the current can be explained if the charge translocating reaction step is preceded by two nonelectrogenic steps: Ca(2+) binding and one conformational transition. Charge translocation in this mode is assigned to one additional conformational change which determines the equilibrium distribution of states. In the Na-Ca e...Continue Reading

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Citations

Sep 17, 2002·Progress in Biophysics and Molecular Biology·Reinaldo DiPolo, Luis Beaugé
Nov 15, 2002·The European Journal of Neuroscience·M MartiniG Rispoli
Mar 5, 2013·Annual Review of Biophysics·Christof GrewerKlaus Fendler
Aug 4, 2007·Progress in Neurobiology·Tamás L Török
Apr 7, 2012·Cellular Signalling·Carlos A Villalba-Galea
Dec 28, 2002·Annals of the New York Academy of Sciences·Andreas HaaseKlaus Hartung
Dec 28, 2002·Annals of the New York Academy of Sciences·Satoshi Matsuoka

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