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Biophys J. 1994 Dec;67(6):2546-57.

Kinetics of the secretory response in bovine chromaffin cells following flash photolysis of caged Ca2+.

Author information

1
Department of Membrane Biophysics, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany.

Abstract

The kinetics of the secretory response in bovine chromaffin cells following flash photolysis of caged Ca2+ were studied by capacitance (Cm) measurements with millisecond time resolution. After elevation of the internal Ca2+ concentration ([Ca2+]i), Cm rises rapidly with one or more exponentials. The time constant of the fastest component decreases for higher [Ca2+]i (range 3-600 microM) over three orders of magnitude before it saturates at approximately 1 ms. The corresponding maximal rates of secretion can be as fast as 100,000 fF/s or 40,000 vesicles/s. There is a Ca(2+)-dependent delay before Cm rises, which may reflect the kinetics of multiple Ca2+ ions binding to the secretory apparatus. The initial rise in Cm is described by models containing a sequence of two to four single Ca(2+)-binding steps followed by a rate-limiting exocytosis step. The predicted Ca2+ dissociation constant (Kd) of a single Ca(2+)-binding site is between 7 and 21 microM. At [Ca2+]i > 30 microM clear indications of a fast endocytotic process complicate the analysis of the secretory response.

PMID:
7696493
PMCID:
PMC1225640
DOI:
10.1016/S0006-3495(94)80744-1
[Indexed for MEDLINE]
Free PMC Article

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