We describe the intracellular distributions of nine essential elements (P, S, Cl, K, Ca, Mn, Fe, Cu, and Zn) found in cardiomyocytes imaged using synchrotron X-ray induced fluorescence. Cardiomyocytes were isolated from rat hearts, flash frozen on Si3N4 windows, freeze-dried, and imaged with approximately 300nm spatial resolution. Distinct longitudinal patterns in cardiomyocytes were most apparent for the elements Fe and Cu, which clearly colocalized. Transverse striations were apparent for P, S, Fe, and Zn, while those for Zn were consistently the most prominent (similar to 10(-3) M) and appeared with a periodicity in the range 1.63-1.75 mu m, the expected length of a sarcomere. Transverse striations for high concentrations of P, Fe, and Zn and low concentrations of S colocalized and coincided with the 1-band of the intact cardiomyocyte. Fluorescence microscopy using FluoZin-3 in intact cardiomyocytes suggests that Zn2+ influx is through sarcolemmal calcium channels and that significant stores of intracellular Zn2+ may be released quickly (< 1 s) into the cytosol. These data collectively suggest that Zn2+ is buffered by structures associated near the T-tubules and/or in the sarcoplasmic reticulum and is found in relative abundance sufficient to act as a modifier of Ca2+ regulation or as a possible signaling messenger for gene expression. (c) 2006 Elsevier Inc. All rights reserved.