Intracellular distributions of essential elements in cardiomyocytes

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 Xuorescence. Cardiomyocytes were isolated from rat hearts, Xash frozen on Si3N4 windows, freeze-dried, and imaged with approximately 300 nm 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 (»10 i3 M) and appeared with a periodicity in the range 1.63–1.75m, 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 I-band of the intact cardiomyocyte. Fluorescence microscopy using FluoZin-3 in intact cardiomyocytes suggests that Zn 2+ inXux is through sarcolemmal calcium channels and that signiWcant stores of intracellular Zn 2+ may be released quickly (<1 s) into the cytosol. These data collectively suggest that Zn 2+ is buVered by structures associated near the T-tubules and/or in the sarcoplasmic reticulum and is found in relative abundance suYcient to act as a modiWer of Ca 2+ regulation or as a possible signaling messenger for gene expression.