The changes in Ca2+ sparks associated with measured modifications of intra-store Ca2+ concentration in skeletal muscle

Launikonis, Bradley S., Zhou, Jingsong, Santiago, Demetrio, Brum, Gustavo and Rios, Eduardo (2006) The changes in Ca2+ sparks associated with measured modifications of intra-store Ca2+ concentration in skeletal muscle. Journal of General Physiology, 128 1: 45-54. doi:10.1085/jgp.200609545

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Author Launikonis, Bradley S.
Zhou, Jingsong
Santiago, Demetrio
Brum, Gustavo
Rios, Eduardo
Title The changes in Ca2+ sparks associated with measured modifications of intra-store Ca2+ concentration in skeletal muscle
Journal name Journal of General Physiology   Check publisher's open access policy
ISSN 0022-1295
Publication date 2006-07
Sub-type Article (original research)
DOI 10.1085/jgp.200609545
Open Access Status File (Publisher version)
Volume 128
Issue 1
Start page 45
End page 54
Total pages 10
Place of publication New York
Publisher Rockefeller University Press
Language eng
Abstract In cardiac muscle and amphibian skeletal muscle, the intracellular Ca2+ release that signals contractile activation proceeds by discrete local packets, which result in Ca2+ sparks. The remarkably stereotyped duration of these release events requires a robustly timed termination mechanism. In cardiac muscle the mechanism of spark termination appears to crucially involve depletion of Ca2+ in the lumen of the sarcoplasmic reticulum (SR), but in skeletal muscle, the mechanism is unknown. We used SEER (shifted excitation and emission ratioing of fluorescence) of SR-trapped mag-indo-1 and confocal imaging of fluorescence of cytosolic rhod-2 to image Ca2+ sparks while reversibly changing and measuring [Ca2+] in the SR ([Ca2+](SR)) of membrane-permeabilized frog skeletal muscle cells. Sparks were collected in cells immersed in a solution promoting production of events at moderate frequency. Just after permeabilization, event frequency was zero, and in 10 minutes it reached close to a steady value. Controlled interventions modified [Ca2+](SR) reversibly between a low value (299 mu M on average in 10 experiments) and a high value (433 mu M, a 45% average increase). This change increased sparks frequency by 93%, spatial width by 7%, rise time by 10%, and peak amplitude by 38% (provided that it was calculated in absolute terms, rather than normalized by resting fluorescence). The changes in event frequency and amplitude were statistically significant. The "strength" of the effect of [Ca2+](SR) on frequency, quantified by decomposition of variance, was < 6%. While the average change in [Ca2+](SR) was limited, it reached up to 200% in individual fibers, without causing massive Ca2+ release or an increase of > 3.5-fold in event frequency. Taken together with existing evidence that depletion is modest during Ca2+ sparks or release elicited by an action potential, the mild effects of [Ca2+](SR) reported here do not support a major role of depletion in either the termination of sparks or the strong inactivation that terminates Ca2+ release at the global level in frog skeletal muscle.
Keyword Physiology
Reticulum Calcium-release
20 Mm Egta
Luminal Calcium
Q-Index Code C1

Document type: Journal Article
Sub-type: Article (original research)
Collections: Excellence in Research Australia (ERA) - Collection
School of Biomedical Sciences Publications
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Citation counts: TR Web of Science Citation Count  Cited 11 times in Thomson Reuters Web of Science Article | Citations
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Created: Wed, 19 Sep 2007, 16:51:01 EST