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Figure 3 The embryonic isoform of smooth muscle myosin heavy chain (SMemb) positive cells are predominantly localized in border zone areas adjacent to viable myocytes. Serial sections from a hibernating myocardial segment were stained for SM1 (A), SM2 (B), SMemb (C) and collagen (D). Arteriolar smooth muscle cells (arrows) express SM1 and SM2 but not SMemb. In contrast, the interstitial SMemb positive cells (C) are negative for SM1 and SM2 and are predominantly located in border areas adjacent to viable myocytes. Areas with extensive collagen deposition show lower SMemb expression (100x). (E) High magnification image of an area from a hibernating myocardial segment stained for SMemb. Note that SMemb expression is localized in spindle-shaped interstitial cells (1,000x).