Spontaneous and evoked intracellular calcium transients in donor-derived myocytes following intracardiac myoblast transplantation
Michael Rubart, … , Hidehiro Nakajima, Loren J. Field
Michael Rubart, … , Hidehiro Nakajima, Loren J. Field
Published September 15, 2004
Citation Information: J Clin Invest. 2004;114(6):775-783. https://doi.org/10.1172/JCI21589.
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Article Cardiology

Spontaneous and evoked intracellular calcium transients in donor-derived myocytes following intracardiac myoblast transplantation

Abstract

Skeletal myoblast transplantation is a potential treatment for congestive heart failure. To study the functional activity of both donor and host myocytes following transplantation, skeletal myoblasts expressing an enhanced green fluorescent protein (EGFP) transgene were transplanted into hearts of nontransgenic recipients, and changes in intracellular calcium concentration ([Ca2+]i) were monitored in donor and host cells. While the vast majority of donor-derived myocytes were observed to be functionally isolated from the host myocardium, a small population of donor myocytes exhibited action potential–induced calcium transients in synchrony with adjacent host cardiomyocytes. In many cases, the durations of these [Ca2+]i transients were heterogeneous compared with those in neighboring host cardiomyocytes. In other studies, EGFP-expressing donor myoblasts were transplanted into the hearts of adult transgenic recipient mice expressing a cardiomyocyte-restricted β-gal reporter gene. A small population of myocytes was observed to express both reporter transgenes, indicating that the transplanted myoblasts fused with host cardiomyocytes at a very low frequency. These cells also expressed connexin43, a component of gap junctions. Thus engraftment of skeletal myoblasts generated spatial heterogeneity of [Ca2+]i signaling at the myocardial/skeletal muscle interface, most likely as a consequence of fusion events between donor myoblasts and host cardiomyocytes.

Authors

Michael Rubart, Mark H. Soonpaa, Hidehiro Nakajima, Loren J. Field

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Figure 4

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Incremental increases in the frequency of field stimulation cause develo...
Incremental increases in the frequency of field stimulation cause development of [Ca2+]i transients (tetanus) in a coupled donor-derived, EGFP-expressing myocyte but not in neighboring cardiomyocytes. (A) Full frame_mode image of a spontaneous [Ca2+]i transient in a rhod-2_loaded heart at 16 days after transplantation of ACT-EGFP skeletal myoblasts; rhod-2 (red) and EGFP (green) signals were superimposed. The white bar marks the position of the line scan_mode data acquisition. Scale bar: 10 μm. (B) Stacked line-scan images of the regions in A indicated by the white line for cells numbered 1 (a coupled, donor-derived myocyte), 2, and 3 (cardiomyocytes). The pacing rate is indicated. (C) Spatially integrated traces of the changes in rhod-2 (red) and EGFP (green) fluorescence for cells 1, 2, and 3. Note that tetanus develops in the coupled donor-derived myocyte, but not in the cardiomyocytes. Identical results were observed when an additional 9 coupled EGFP-expressing myocytes were analyzed. *Ca2+ waves; #dual-peak elevations of [Ca2+]i transients due to superimposition of spontaneous and field stimulation_induced transients. (D) Sustained rapid stimulation induced a decline of [Ca2+]i in in vitro_differentiated skeletal myocytes. Line-scan images from two skeletal myocytes during rest and during continuous field stimulation at 10 Hz for 5 minutes were obtained, and spatially averaged rhod-2 intensities were plotted as function of time. Rapid stimulation causes an initial elevation of [Ca2+]i followed by a slow decay.