English
 
User Manual Privacy Policy Disclaimer Contact us
  Advanced SearchBrowse

Item

ITEM ACTIONSEXPORT

Released

Journal Article

Rapid charge translocation by the cardiac Na+-Ca2+ exchanger after a Ca2+ concentration jump

MPS-Authors
/persons/resource/persons48141

Kappl,  Michael
Department of Biophysical Chemistry, Max Planck Institute of Biophysics, Max Planck Society;

/persons/resource/persons137696

Hartung,  Klaus
Department of Biophysical Chemistry, Max Planck Institute of Biophysics, Max Planck Society;

External Ressource
No external resources are shared
Fulltext (public)
There are no public fulltexts stored in PuRe
Supplementary Material (public)
There is no public supplementary material available
Citation

Kappl, M., & Hartung, K. (1996). Rapid charge translocation by the cardiac Na+-Ca2+ exchanger after a Ca2+ concentration jump. Biophysical Journal, 71(5), 2473-2485. doi:10.1016/S0006-3495(96)79441-9.


Cite as: http://hdl.handle.net/21.11116/0000-0007-64A8-B
Abstract
The kinetics of N+-Ca2+ exchange current after a cytoplasmic Ca2+ concentration jump (achieved by photolysis of DM-nitrophen) was measured in excised giant membrane patches from guinea pig or rat heart. Increasing the cytoplasmic Ca2+ concentration from 0.5 microM in the presence of 100 mM extracellular Na+ elicits an inward current that rises with a time constant tau1 < 50 microseconds and decays to a plateau with a time constant tau2 = 0.65 +/- 0.18 ms (n = 101) at 21 degrees C. These current signals are suppressed by Ni2+ and dichlorobenzamil. No stationary current, but a transient inward current that rises with tau1 < 50 microseconds and decays with tau2 = 0.28 +/- 0.06 ms (n = 53, T = 21 degrees C) is observed if the Ca2+ concentration jump is performed under conditions that promote Ca2+-Ca2+ exchange (i.e., no extracellular Na+, 5 mM extracellular Ca2+). The transient and stationary inward current is not observed in the absence of extracellular Ca2+ and Na+. The application of alpha-chymotrypsin reveals the influence of the cytoplasmic regulatory Ca2+ binding site on Ca2+-Ca2+ and forward Na+-Ca2+ exchange and shows that this site regulates both the transient and stationary current. The temperature dependence of the stationary current exhibits an activation energy of 70 kj/mol for temperatures between 21 degrees C and 38 degrees C, and 138 kj/mol between 10 degrees C and 21 degrees C. For the decay time constant an activation energy of 70 kj/mol is observed in the Na+-Ca2+ and the Ca(2+)-Ca2+ exchange mode between 13 degrees C and 35 degrees C. The data indicate that partial reactions of the Na+-Ca2+ exchanger associated with Ca2+ binding and translocation are very fast at 35 degrees C, with relaxation time constants of about 6700 s-1 in the forward Na+-Ca2+ exchange and about 12,500 s-1 in the Ca2+-Ca2+ exchange mode and that net negative charge is moved during Ca2+ translocation. According to model calculations, the turnover number, however, has to be at least 2-4 times smaller than the decay rate of the transient current, and Na+ inward translocation appears to be slower than Ca2+ outward movement.