1. ¹Department of Pediatrics, Division of Cardiology, Wells Center for Pediatric Research, Indianapolis, Indiana, USA
2. ²Department of Medicine, Division of Cardiology, Krannert Institute of Cardiology, Indiana University School of Medicine, Indianapolis, Indiana, USA
3. ³Department of Medicine, Division of Hematology/Oncology, Indiana University School of Medicine, Indianapolis, Indiana, USA
4. ⁴Department of Microbiology/Immunology, Indiana University School of Medicine, Indianapolis, Indiana, USA

Correspondence: Michael Rubart, Wells Center for Pediatric Research, 1044 West Walnut Street, Indianapolis, Indiana 46202, USA. E-mail: mrubartv@iupui.edu

Received 2 February 2008; Accepted 5 March 2008; Published online 22 April 2008.

Abstract

The cardiomyogenic potential of adult bone marrow (BM) cells after being directly transplanted into the ischemically injured heart remains a controversial issue. In this study, we investigated the ability of transplanted BM cells to develop intracellular calcium ([Ca²⁺]_i) transients in response to membrane depolarization in situ. Low-density mononuclear (LDM) BM cells, c-kit-enriched (c-kit^enr) BM cells, and highly enriched lin^– c-kit⁺ BM cells were obtained from adult transgenic mice ubiquitously expressing enhanced green fluorescent protein (EGFP), and injected into peri-infarct myocardiums of nontransgenic mice. After 9–10 days the mice were killed, and the hearts were removed, perfused in Langendorff mode, loaded with the calcium-sensitive fluorophore rhod-2, and subjected to two-photon laser scanning fluorescence microscopy (TPLSM) to monitor action potential–induced [Ca²⁺]_i transients in EGFP-expressing donor-derived cells and non-expressing host cardiomyocytes. Whereas spontaneous and electrically evoked [Ca²⁺]_i transients were found to occur synchronously in host cardiomyocytes along the graft–host border and in areas remote from the infarct, they were absent in all of the >3,000 imaged BM-derived cells that were located in clusters throughout the infarct scar or peri-infarct zone. We conclude that engrafted BM-derived cells lack attributes of functioning cardiomyocytes, calling into question the concept that adult BM cells can give rise to substantive cardiomyocyte regeneration within the infarcted heart.