Modulation of focal and global Ca2+ release in calsequestrin-overexpressing mouse cardiomyocytes

Wei Wang, Lars Cleemann, Larry Jones, Martin Morad

Research output: Contribution to journalArticle

31 Citations (Scopus)

Abstract

1. Focal and global Ca2+ releases were monitored in voltage-clamped control and hypertrophied calsequestrin (CSQ)-overexpressing mouse cardiomyocytes, dialysed with fluo-3, using rapid (120-240 frames s-1) two-dimensional confocal imaging. 2. Spontaneous focal Ca2+ releases (Ca2+ sparks) were absent or significantly reduced in frequency in hypertrophied myocytes of CSQ-overexpressing mice compared to their age-matched controls. Sporadic Ca2+ sparks seen in CSQ-overexpressing myocytes had intensities and durations similar to those of controls although quantitative analysis showed a trend towards more diffuse focal releases. Activation of Ca2+ current (I(Ca)) failed to produce the typical sarcomeric Ca2+ striping pattern consistently seen in control myocytes. Instead, focal Ca2+ releases appeared as a disorganized patchwork of diffuse or 'woolly' fluorescence signals, resulting in slowly developing and reduced global Ca2+ transients. 4. Although the density of I(Ca) in CSQ-overexpressing myocytes was only slightly smaller than that of controls, the inactivation kinetics of the current were greatly reduced, consistent with the much smaller rate of rise of cytosolic Ca2+. 5. Enhancement of I(Ca) by elevation of [Ca2+](o) from 2 to 10 mM or addition of 3 μM isoproterenol (isoprenaline) failed to normalize the frequency of spontaneous Ca2+ sparks at rest or the pattern and the magnitude of I(Ca)-gated Ca2+ transients. Isoproterenol was somewhat more effective than elevation of [Ca2+](o). 6. In sharp contrast, low (0.5 mM) caffeine concentrations that produced no measurable effects on I(Ca) or Ca2+ transients in control myocytes, re-established spontaneous focal Ca2+ releases in CSQ-overexpressing cells, triggered large I(Ca)-gated cellular Ca2+ transients, and strongly enhanced the kinetics of inactivation of I(Ca). 7. Our data suggest that impaired Ca2+ signalling in CSQ-overexpressing myocytes results from reduced co-ordination and decreased frequency of Ca2+ sparks. The impaired Ca2+ signalling could not be restored by procedures that increased I(Ca), but was mostly restored in the presence of caffeine, which may alter the Ca2+ sensitivity of the ryanodine receptor.

Original languageEnglish (US)
Pages (from-to)399-414
Number of pages16
JournalJournal of Physiology
Volume524
Issue number2
StatePublished - Apr 15 2000
Externally publishedYes

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Calsequestrin
Cardiac Myocytes
Muscle Cells
Isoproterenol
Caffeine
Ryanodine Receptor Calcium Release Channel
Fluorescence

ASJC Scopus subject areas

  • Physiology

Cite this

Modulation of focal and global Ca2+ release in calsequestrin-overexpressing mouse cardiomyocytes. / Wang, Wei; Cleemann, Lars; Jones, Larry; Morad, Martin.

In: Journal of Physiology, Vol. 524, No. 2, 15.04.2000, p. 399-414.

Research output: Contribution to journalArticle

Wang, Wei ; Cleemann, Lars ; Jones, Larry ; Morad, Martin. / Modulation of focal and global Ca2+ release in calsequestrin-overexpressing mouse cardiomyocytes. In: Journal of Physiology. 2000 ; Vol. 524, No. 2. pp. 399-414.
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