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  Pre-Steady-State Kinetics of Ba-Ca Exchange Reveals a Second Electrogenic Step Involved in Ca2+ Translocation by the Na-Ca Exchanger

Haase, A., & Hartung, K. (2009). Pre-Steady-State Kinetics of Ba-Ca Exchange Reveals a Second Electrogenic Step Involved in Ca2+ Translocation by the Na-Ca Exchanger. Biophysical Journal, 96(11), 4571-4580. doi:10.1016/j.bpj.2009.03.017.

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 Creators:
Haase, Andreas1, Author           
Hartung, Klaus1, Author           
Affiliations:
1Department of Biophysical Chemistry, Max Planck Institute of Biophysics, Max Planck Society, ou_2068289              

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 Abstract: Kinetic properties of the Na-Ca exchanger (guinea pig NCX1) expressed in Xenopus oocytes were investigated with excised membrane patches in the inside-out configuration and photolytic Ca2+ concentration jumps with either 5 mM extracellular Sr2+ or Ba2+. After a Ca2+ concentration jump on the cytoplasmic side, the exchanger performed Sr-Ca or Ba-Ca exchange. In the Sr-Ca mode, currents are transient and decay in a monoexponential manner similar to that of currents in the Ca-Ca exchange mode described before. Currents recorded in the Ba-Ca mode are also transient, but the decay is biphasic. In the Sr-Ca mode the amount of charge translocated increases at negative potentials in agreement with experiments performed in the Ca-Ca mode. In the Ba-Ca mode the total amount of charge translocated after a Ca2+ concentration jump is ∼4 to 5 times that in Ca-Ca or Sr-Ca mode. In the Ba-Ca mode the voltage dependence of charge translocation depends on the Ca2+ concentration on the cytosolic side before the Ca2+ concentration jump. At low initial Ca2+ levels (∼0.5 μM), charge translocation is voltage independent. At a higher initial concentration (1 μM Ca2+), the amount of charge translocated increases at positive potentials. Biphasic relaxation of the current was also observed in the Ca-Ca mode if the external Ca2+ concentration was reduced to ≤0.5 mM. The results reported here and in previous publications can be described by using a 6-state model with two voltage-dependent conformational transitions.

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Language(s): eng - English
 Dates: 2008-08-282009-03-172009-06-03
 Publication Status: Published in print
 Pages: 10
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1016/j.bpj.2009.03.017
PMID: 19486679
PMC: PMC2711458
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Title: Biophysical Journal
  Other : Biophys. J.
Source Genre: Journal
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Publ. Info: Cambridge, Mass. : Cell Press
Pages: - Volume / Issue: 96 (11) Sequence Number: - Start / End Page: 4571 - 4580 Identifier: ISSN: 0006-3495
CoNE: https://pure.mpg.de/cone/journals/resource/954925385117