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J. Cell Biol.,
Volume 140, Number 2, January 26, 1998 325-334
University of Padova, Department of Biomedical Sciences, CNR Center for Biomembranes, I-35121 Padova, Italy
ICRAC (the best characterized Ca2+ current
activated by store depletion) was monitored concurrently for the first time with [Ca2+] changes in internal
stores. To establish the quantitative and kinetic relationship between these two parameters, we have developed a novel means to clamp [Ca2+] within stores of intact cells at any level. The advantage of this approach,
which is based on the membrane-permeant low-affinity Ca2+ chelator N,N,N
,N
-tetrakis (2-pyridylmethyl)ethylene diamine (TPEN), is that [Ca2+] within the ER can
be lowered and restored to its original level within
10-15 s without modifications of Ca2+ pumps or release
channels. Using these new tools, we demonstrate here
that Ca2+ release-activated Ca2+ current (ICRAC) is activated (a) solely by reduction of free [Ca2+] within the
ER and (b) by any measurable decrease in [Ca2+]ER.
We also demonstrate that the intrinsic kinetics of inactivation are relatively slow and possibly dependent on
soluble factors that are lost during the whole-cell recording.
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