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Intercalated clear cells or pale cells in the sinus node of canine hearts? An ultrastructural study
S Stoletzki1, A Schmiedl, J Richter
1Department of Anatomy, Division of Electron Microscopy, University of Göttingen, D-37075 Göttingen, Germany.
Insights
Intercalated clear cells are a distinct sinuatrial node cell type found in non-ischemic tissue. Pale cells represent damaged sinus nodal cells, differing significantly from clear cells under ischemic conditions.
Area of Science:
- Cardiovascular Biology
- Cellular Ultrastructure
- Cardiac Electrophysiology
Background:
- The sinuatrial node's ultrastructure exhibits variability, with reported differences attributed to intercalated clear cells and pale cells.
- Understanding these cell types is crucial for interpreting sinuatrial node function and pathology.
Purpose of the Study:
- To differentiate between intercalated clear cells and pale cells in the canine sinuatrial node.
- To elucidate the ultrastructural characteristics of these cell types under non-ischemic and ischemic conditions.
Main Methods:
- Canine hearts were subjected to cardioplegic arrest using St. Thomas or HTK solutions.
- Sinus node tissue was fixed via immersion or perfusion for electron microscopy.
- Ultrastructural analysis was performed on non-ischemic and ischemic sinuatrial node samples.
Main Results:
- Three sinuatrial node cell types were identified post-cardioplegic arrest: typical nodal, transitional, and intercalated clear cells.
- Intercalated clear cells (<1% of cells) exhibited poorly developed contractile apparatus and mitochondrial variations, distinct from ischemic changes.
- Ischemia (15-25 min at 25°C) induced significant alterations in >10% of nodal cells (pale cells), including mitochondrial swelling and cell swelling.
Conclusions:
- Intercalated clear cells are a normal component of non-ischemic sinuatrial node tissue.
- Pale cells represent ischemically damaged sinus nodal cells, characterized by distinct ultrastructural alterations.
- The study clarifies the morphological differences between intercalated clear cells and pale cells, resolving literature discrepancies.
Abstract:
Two types of sinus nodal cells were responsible for the main differences in the literature concerning the ultrastructure of the sinuatrial node: the intercalated clear cells and pale cells. Canine hearts were arrested by (1) aortic cross clamping, (2) coronary perfusion with the cardioplegic solution St. Thomas, and (3) coronary perfusion with the cardioplegic solution HTK (Custodiol(R)). After fixation by immersion or perfusion the sinus node tissue was prepared for electron microscopy. Following cardioplegic arrest and perfusion fixation, three nodal cell types in the non-ischemic sinuatrial node were observed: typical nodal cells, transitional cells, and intercalated clear cells. Less than 1% of the non-ischemic sinuatrial cells were intercalated clear cells, surrounded by typical nodal cells or transitional cells. The contractile apparatus of the intercalated clear cells was extremely poorly developed. Great structural variations in the mitochondria were observed in intercalated clear cells, variations that would not appear under conditions of ischemia. In contrast, after 15-25 min of ischemia at 25 degrees C the appearance of the sinus nodal cells was strikingly different from that of the non-ischemic sinuatrial cells. More than 10% of the nodal cells showed typical ischemic alterations, e.g., mitochondrial swelling, clumping of nuclear chromatin, loss of glycogen particles, and cell swelling in varying degrees. Because they look very pale, these nodal cells have been described as pale cells in the literature. Intercalated clear cells appear mainly in non-ischemic nodal tissue. Pale cells are ischemically damaged sinus nodal cells.