Gap junctional communication between MSCs and ECs in matrigel capillaries. (A) Images show red fluorescence of mitochondria-stained MSCs (arrow) juxtaposed with GFP-expressing capillaries (green). MTDR, Mitotracker deep red. Capillaries were loaded with calcein (purple). By switching fluorescence filters, single MSC (dashed ovals) were identified by red mitochondrial fluorescence under calcein loaded conditions. Note that 20 minutes after calcein fluorescence in the MSC was photobleached, fluorescence was recovered in control (CT) but not in GA-treated capillaries. Bar = 10 μm. (B,C) Time course of FRAP in single EC-associated MSCs in untreated (CT), GA-treated (GA), and gap peptide–treated (GP) cultures, and for single EC-associated MSCs in GFP-Cx43T154A- (Cx43mt) or empty vector–expressing capillaries (VECs). (D) Group data show FRAP in MSCs 20 minutes after bleaching. Mean plus or minus SD. *P < .05 relative to CT. (E) Group data show capillary density in 4-day-old capillaries to which MSCs were added at 1:1 ratio to EC on day 1. WT, wild-type; other abbreviations are as above. Mean plus or minus SD; n indicates number of experiments. *P < .05 relative to WT. (F) Immunoblot for cleaved caspase-3 in 4-day-old capillaries exposed to MSCs as above. Actin expression is shown in the bottom panel. Replicated 3 times.