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 2

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Donor-derived myocytes retain skeletal muscle_like functional characteri...
Donor-derived myocytes retain skeletal muscle_like functional characteristics following transplantation into the ventricular myocardium. (A) Relative changes in rhod-2 fluorescence (ΔF) as a function of time in donor-derived, EGFP-expressing myocytes (red, blue, and black traces) and a neighboring host ventricular cardiomyocyte (green trace) during electrical field stimulation (2 Hz). The relative changes in rhod-2 fluorescence were normalized such that 0 represents the pre-stimulus fluorescence intensity and 1 represents the peak fluorescence intensity. (B) Relative changes in rhod-2 fluorescence in in vitro_differentiated skeletal myocytes (red and blue traces) following field stimulation (2 Hz; data normalized as in A). (C) Quantitative comparisons of [Ca2+]i transient parameters from donor-derived, EGFP-expressing myocytes (white bars) vs. in vitro_differentiated skeletal myocytes (gray bars) following field stimulation (2 Hz). Values are mean ± SEM of 12 donor-derived, EGFP-expressing myocytes distributed among 4 hearts and from 7 in vitro_differentiated, WT skeletal myocytes after 7_10 days of culture. There were no significant differences between the groups (P > 0.05). (D) Spatially integrated traces of the changes in rhod-2 (red) and EGFP (green) fluorescence during field stimulation at incrementally increasing rates in a donor-derived, EGFP-expressing myocyte in situ (upper panel), in a neighboring host cardiomyocyte (middle panel), and in an in vitro_differentiated skeletal myocyte (lower panel). Note the development of tetanus in the donor-derived skeletal myocyte in situ and in the in vitro_differentiated skeletal myocyte, but not in the cardiomyocyte.