T-jump study of calcium binding kinetics of calcium chelators
1997; Elsevier BV; Volume: 22; Issue: 4 Linguagem: Inglês
10.1016/s0143-4160(97)90064-6
ISSN1532-1991
Autores Tópico(s)Receptor Mechanisms and Signaling
ResumoRecent experimental studies have investigated the kinetic competition between calcium chelators and the secretion apparatus at a fast central synapse. Simultaneously, mathematical modelling studies indicate the importance of a quantitative knowledge of the binding kinetics of the chelators in studying fast physiological processes operating on a millisecond time scale. Using the temperature-jump relaxation method, I have studied the in vitro kinetics of Bis-Fura-2, Furaptra, Fluo-3, Calcium-Green-1, Calcium-Green-5N, Calcium-Orange-5N as well as EGTA, BAPTA and H-EDTA in conditions which are identical to those implemented in our patch clamp recordings, i.e. 100-140 mM CsCl, 20-40 mM Cs-HEPES, 8 mM NaCl, pH = 7.2 at 22 degrees C. The results can be summarized as follows: all fluorescent indicators have on rates in the range of 10(8)-10(9) M-1s-1. They differ significantly with respect to their off-rates from each other according to their affinities, ranging from 100 s-1 up to 26,000 s-1. BAPTA is kinetically almost indistinguishable from Fura-2. EGTA and H-EDTA have small binding rate constants for calcium in the range of 3 x 10(6) M-1s-1 since, at pH 7.20, protons need to be dissociated from the chelators before they can bind calcium ions.
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