Objective: The purpose of the study was to investigate the development of electrical transmission across human adult bone marrow-derived mesenchymal stem cells (hMSCs) during long-term co-incubation with cardiomyocytes (CMCs).
Methods: Neonatal rat CMCs were cultured in multi-electrode array dishes. A conduction block was induced by creating a central acellular channel, yielding two asynchronously beating CMC fields. Enhanced green fluorescent protein (eGFP)-labeled hMSCs from ischemic heart disease patients (n=8), eGFP-labeled hMSCs having RNA interference-mediated connexin43 (Cx43) knockdown (n=6), 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine (Dil)-labeled CMCs (n=6), or no cells (n=9) were seeded in the channel. Assessment of conduction velocity (CV), Cx expression and localization, gap junctional coupling, and intracellular electrical recordings were performed for up to 14 days.
Results: Resynchronization of the two CMC fields occurred within 24 h after seeding of hMSCs. CV across hMSCs increased from 1.4+/-0.4 cm/s at day 7 to 3.5+/-0.1 cm/s (p<0.05) at day 14. CV across seeded CMCs was 16.8+/-0.2 cm/s throughout this period. No resynchronization occurred in the absence of seeded cells. Knockdown of Cx43 in hMSCs abolished conduction across the channel completely. Time-dependent increase of CV across hMSCs was associated with increased Cx43 mRNA and protein expression resulting in increased gap junctional coupling. Intracellular recordings in coupled hMSCs showed increased conducted action potential (AP) amplitude, lower resting membrane potential, and decreased duration of conducted AP (p<0.05, day 14 versus day 1).
Conclusions: CV across hMSCs increases progressively after 7 days of co-incubation with CMCs, most likely via improved electrotonic interaction. This is associated with increased Cx43 expression, increased functional gap junctional coupling, and enhanced intercellular electrical coupling between hMSCs and CMCs.