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 6

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Connexin43 immune reactivity between cells arising from myoblast-cardiom...
Connexin43 immune reactivity between cells arising from myoblast-cardiomyocyte fusion events and host cardiomyocytes. Ten-micron sections prepared from MHC-nLAC hearts transplanted with ACT-EGFP skeletal myoblasts were stained with X-GAL and reacted with an anti-connexin43 Ab, followed by a rhodamine-conjugated secondary Ab. (A_C) Connexin43 is present at the junction of host cardiomyocytes. Host cardiomyocytes are identified by blue nuclear staining (A) and the absence of EGFP fluorescence (B). (C) A higher-magnification image of connexin43 immune reactivity in the boxed region is shown (red signal). (D_F) Connexin43 is absent between donor-derived skeletal myoblasts. Donor-derived myocytes are identified by the absence of blue nuclear staining (D) and the presence of green fluorescence (E). (F) A higher-magnification image of the boxed region after staining for connexin43 immune reactivity. Note the absence of punctate red signal. (G_I) Connexin43 is present at the junction between cells derived from myocyte-cardiomyocyte fusion events and host cardiomyocytes. Cells arising from myocyte-cardiomyocyte fusion events are identified by the presence of blue nuclear staining (G) and EGFP fluorescence (H). Host cardiomyocytes are identified by the presence of nuclear β-gal activity and the absence of EGFP fluorescence. (I) A higher-magnification image of connexin43 immune reactivity in the boxed region. Arrows mark punctate red signal, indicative of the presence of connexin43 (and hence, the presence of gap junctions). (J_L) Additional example of connexin43; arrows indicate the position of the gap junctions. Scale bars: 10 μm.