Figure 8

(a) Full-frame TPME image (left panel) and line-scan image of myocardium in the infarct border zone of an engrafted heart. Host cardiomyocytes readily exhibit electrically evoked, synchronized calcium transients in a 11 fashion during field stimulation at 4 Hz. Under these conditions, cardiomyocyte excitation is independent of cell-to-cell action potential propagation. Calcium transients appear as ripple-like wavefronts. Scale bar, 20 microns. (b) Electrical field stimulation of the same heart did not induce calcium transients in eGFP-expressing donor cell-derived cells or in non-expressing cells in an area contiguous to that shown in panel A, suggesting absence of functional cardiomyocytes in this field of view. Note the two horizontal red lines in the left panel which correspond to localized photodamage that had occurred during preceding line scans and are not to be confused with action potential-induced calcium transients. (c–d) Time course of the red (rhod-2) and green (eGFP) fluorescence in host cardiomyocytes (c) and donor-derived cells (d) obtained by spatially averaging the respective line-scans in panels a and b, respectively. No action potential-induced calcium transients were recorded in eGFP-expressing cells, whereas host cardiomyocytes show synchronized transients with identical kinetics.