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© The Rockefeller University Press, 0021-9525/1998//325 $5.00
The Journal of Cell Biology, Volume 140, Number 2, , 1998 325-334

Article

Capacitative Ca2+ Entry Is Closely Linked to the Filling State of Internal Ca2+ Stores: A Study Using Simultaneous Measurements of ICRAC and Intraluminal [Ca2+]



Aldebaran M. Hofer, Cristina Fasolato, and Tullio Pozzan

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.

Abbreviations used in this paper: BAPTA, 1,2-bis (2-amino-phenoxy)ethane-N,N,N',N-tetraacetic acid; ICRAC, Ca2+ release–activated Ca2+ current; InsP3, inositol 1,4,5-trisphosphate; InsP4, inositol 1,3,4,5-tetrakisphosphate; TPEN, N,N,N',N'-tetrakis (2-pyridylmethyl)ethylene diamine.

Address all correspondence to Tullio Pozzan University of Padova, Department of Biomedical Sciences, CNR Center for Biomembranes, Viale G. Colombo, 3, I-35121 Padova, Italy. Tel.: +39-49-827-6065. Fax: +39-49-827-6049. E-mail:pozzan{at}civ.bio.unipd.it


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