Ultrastructural cytochemistry of atrial muscle cells: IX. Reactivity of specific granules in cultured cardiocytes

A technique for the culture of neonatal (2- to 3-day-old) rat cardiocytes is described. With this technique, ventricular cardiocytes started beating earlier and lived longer, atrial cardiocytes degenerating after 10 days of culture. Specific granules, mostly of the A type, were present in atrial but not ventricular cardiocytes at all time intervals. These specific granules were argentaphobic when stained according to the periodic acid-thiocarbohydrazide-silver proteinate technique of Thiery. The core of these granules was moderately positive after staining fine sections with phosphotungstic acid at low pH. A similar reaction was shown in both atria and ventricle by the cell coat, residual bodies (C-granules) and Z-discs. The Golgi complex was more extensively stained by phosphotungstic acid in atrial than in ventricular cultured cardiocytes or in atrial and ventricular cardiocytes of young (3- and 13-day-old) rats in situ. Multivesicular bodies with a dense core, identical to those already noted in the cells of various endocrine glands, and thought to be crinophagic, were present, as in atrial cardiocytes in situ, in cultured atrial but not ventricular cardiocytes. They were silver negative. Their dense core, as in situ, reacted to phosphotungstic acid but their matrix, contrary to classical multivesicular bodies without a dense core, did not. Numerous, small, phosphotungstic acid-positive vesicles were present in cultured atrial and, to a lesser extent, in cultured ventricular cardiocytes. Vesicles of the same type were rare in either atrial of ventricular cardiocytes of young rats in situ. Glycogen, as revealed by the periodic acid Schiff and Thiery techniques, was equally abundant in cardiocytes in situ and in 1-day-old cultures of cultured cardiocytes from atria and ventricle. These results indicate that specific granules of cultured atrial cardiocytes are probably made up, as in situ, of glycoproteins.