Electron probe microanalysis of elemental composition of mouse cardiac myocytes during post‐natal maturation

Elemental concentrations in the cytoplasm and nucleus of post‐natal mouse myocytes were measured at 2, 4, 8, 16, 32 days and in adults using electron probe X‐ray microanalysis. Using an analysis of variance test, significant age dependent changes were found in intracellular potassium, sulfur, phosphorus, and chlorine concentations (mg/kg dry weight), while sodium and magnesium concentrations did not show significant changes. The application of t tests following linear regression analyses (age versus concentration for each element) did, however, give a significant slope for cytoplasmic sodium, potassium, sulfur, and phosphorus values. The findings correspond closely with an emission spectroscopy‐titrimetric study of whole heart ventricle of the same developmental period (Hazelwood and Nichols, '70).