MH 073-074 Heart

Purkinje Fibers
(H&E)

Purkinje fibers are specialized cardiac muscle cells that conduct electrical signals that coordinate synchronized contractions of the ventricles. Hematoxylin and eosin (H&E) staining reveals distinctive morphological features that differentiate Purkinje fibers from ordinary cardiac myocytes.

This section passes through the aortic valve located between the left ventricle (on the right side) and the aorta (on the left side).

Anatomy:

• Primary Location: Lighter stained fibers (#1,#2,#3) immediately beneath the endocardium of the ventricular wall
• Distribution: Form extensive networks throughout the ventricular walls

Cellular Morphology:

• Cell Size: Significantly larger than normal cardiac myocytes (2-3 times the diameter)
• Cytoplasm: Lighter, pale pink staining compared to normal cardiac myocytes
  • Glycogen: Markedly elevated glycogen stores (unstained, appearing as clear areas)
    • Provides readily available energy for electrical activity
• Myofibrils: Lower content reflects their specialized role in conduction rather than contractile function
  • Striations: Difficult to see due to reduced myofibrillar content
• Intercalated Discs: More prominent than in ventricular myocytes due to lighter cytoplasmic staining

Purkinje Fibers
(Phosphotungstic Acid/Hematoxylin)

Phosphotungstic Acid/Hematoxylin (PTAH) staining provides enhanced visualization of muscle striations and cellular organization. Cardiac muscle cells stain a dark gray/purple, while collagen and other connective tissues appear pink/red.

• Purkinje Fibers:
  • Primary Location: Lighter stained cells (#1,#2,#3) immediately beneath the endocardium of both ventricles
  • Cell Size: Significantly larger than normal cardiac myocytes (2-3 times the diameter)
  • Cytoplasm: Lighter gray to pale purple staining compared to normal myocytes
    • Glycogen: Markedly elevated glycogen stores (unstained, appearing as clear areas)
    • Myofibrils: Lower content makes striations more evident
• Cardiac Myocytes:
  • Cytoplasm: Darker gray/purple compared to Purkinje fibers
    • Myofibrils: Densely packed with prominent cross-striations observed in regions more lightly stained

Technical Note: The alternating dark and light bands observed within the left ventricular myocardium and the tunica media of the aorta represent sectioning artifacts rather than histological features.