|
|
|
|
|
|
|
||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Department of Physiology & Biophysics, University of Washington, Seattle, Washington 98195-7290; and * Image Analysis
Laboratory, Fred Hutchinson Cancer Research Center, Seattle, Washington 98104
Calcium can activate mitochondrial metabolism, and the possibility that mitochondrial Ca2+ uptake
and extrusion modulate free cytosolic [Ca2+] (Cac) now
has renewed interest. We use whole-cell and perforated patch clamp methods together with rapid local perfusion to introduce probes and inhibitors to rat chromaffin cells, to evoke Ca2+ entry, and to monitor Ca2+-activated currents that report near-surface [Ca2+]. We
show that rapid recovery from elevations of Cac requires both the mitochondrial Ca2+ uniporter and the
mitochondrial energization that drives Ca2+ uptake
through it. Applying imaging and single-cell photometric methods, we find that the probe rhod-2 selectively
localizes to mitochondria and uses its responses to
quantify mitochondrial free [Ca2+] (Cam). The indicated resting Cam of 100-200 nM is similar to the resting Cac reported by the probes indo-1 and Calcium
Green, or its dextran conjugate in the cytoplasm. Simultaneous monitoring of Cam and Cac at high temporal resolution shows that, although Cam increases less
than Cac, mitochondrial sequestration of Ca2+ is fast
and has high capacity. We find that mitochondrial Ca2+
uptake limits the rise and underlies the rapid decay of
Cac excursions produced by Ca2+ entry or by mobilization of reticular stores. We also find that subsequent export of Ca2+ from mitochondria, seen as declining Cam,
prolongs complete Cac recovery and that suppressing
export of Ca2+, by inhibition of the mitochondrial Na+/
Ca2+ exchanger, reversibly hastens final recovery of
Cac. We conclude that mitochondria are active participants in cellular Ca2+ signaling, whose unique role is
determined by their ability to rapidly accumulate and
then release large quantities of Ca2+.
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
This article has been cited by other articles:
|
|
