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Kinetic studies of Ca2+ binding and Ca2+ clearance in the cytosol of adrenal chromaffin cells

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Xu,  T.
Department of Membrane Biophysics, MPI for biophysical chemistry, Max Planck Society;

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Naraghi,  M.
Department of Membrane Biophysics, MPI for biophysical chemistry, Max Planck Society;

Kang,  H. G.
Department of Membrane Biophysics, MPI for biophysical chemistry, Max Planck Society;

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Neher,  E.
Department of Membrane Biophysics, MPI for biophysical chemistry, Max Planck Society;

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Citation

Xu, T., Naraghi, M., Kang, H. G., & Neher, E. (1997). Kinetic studies of Ca2+ binding and Ca2+ clearance in the cytosol of adrenal chromaffin cells. Biophysical Journal, 73(1), 532-545. doi:10.1016/S0006-3495(97)78091-3.


Cite as: https://hdl.handle.net/11858/00-001M-0000-0012-FF63-1
Abstract
The Ca2+ binding kinetics of fura-2, DM-nitrophen, and the endogenous Ca2+ buffer, which determine the time course of Ca2+ changes after photolysis of DM-nitrophen, were studied in bovine chromaffin cells. The in vivo Ca2+ association rate constants of fura-2, DM-nitrophen, and the endogenous Ca2+ buffer were measured to be 5.17 x 10(8) M-1 s-1, 3.5 x 10(7) M-1 s-1, and 1.07 x 10(8) M-1 s-1, respectively. The endogenous Ca2+ buffer appeared to have a low affinity for Ca2+ with a dissociation constant around 100 microM. A fast Ca2+ uptake mechanism was also found to play a dominant role in the clearance of Ca2+ after flashes at high intracellular free Ca2+ concentrations ([Ca2+]), causing a fast [Ca2+]i decay within seconds. This Ca2+ clearance was identified as mitochondrial Ca2+ uptake. Its uptake kinetics were studied by analyzing the Ca2+ decay at high [Ca2+]i after flash photolysis of DM-nitrophen. The capacity of the mitochondrial uptake corresponds to a total cytosolic Ca2+ load of approximately 1 mM.