Journal of Structural Biology 155 (2006) 12–21 www.elsevier.com/locate/yjsbi 1047-8477/$ - see front matter  2006 Elsevier Inc. All rights reserved. doi:10.1016/j.jsb.2005.11.017 Intracellular distributions of essential elements in cardiomyocytes Bradley M. Palmer a,¤ , Stefan Vogt c , Zengyi Chen b , Richard R. Lachapelle b , Martin M. LeWinter a,b a Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, VT 05405, USA b Department of Medicine, University of Vermont, Burlington, VT 05405, USA c Experimental Facilities Division, Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439, USA Received 25 May 2005; received in revised form 21 November 2005; accepted 30 November 2005 Available online 30 March 2006 Abstract 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 Si 3 N 4 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 ¡3 M) and appeared with a periodicity in the range 1.63–1.75 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 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.  2006 Elsevier Inc. All rights reserved. Keywords: Calcium; Iron; Copper; Zinc 1. Introduction Cardiomyocytes are heart muscle cells specialized to repeatedly produce contractile force. The study of cardio- myocyte function has been compartmentalized roughly into areas of electrophysiology, force production, metabolism, and gene expression. Signaling mechanisms also exist within and between these functional compartments and govern overall cardiomyocyte performance and mainte- nance (Bers, 2001). Some signaling mechanisms are well characterized and are known to involve speciWc ions as sig- naling messengers. For example, membrane depolarization leads to a rapid rise in intracellular free Ca 2+ concentration, which directly activates force production (Bers, 2001). Other currently uncharacterized signaling mechanisms, such as those modulating gene expression, may likewise involve other ions or metalloproteins directly activating transcription factors (Bird et al., 2000, 2003; DeMoor and Koropatnick, 2000; O’Halloran, 1993; Outten and O’Hallo- ran, 2001) or more distal portions of transcription and/or translation pathways (Andrews, 2001; Finney and O’Hallo- ran, 2003; Outten and O’Halloran, 2001; Pyle, 1993; Verhaegh et al., 1998). Although the concentrations of several low atomic num- bered elements (Na, Mg, P, S, Cl, K, and Ca) have been pre- viously examined in cardiomyocyte myoWlaments and organelles (Bond et al., 1994; Isenberg et al., 1996; Keller et al., 1995), detailed spatial distributions of these and other elements would further elucidate the structural availability of elements and their ionic forms as specialized signaling messengers in the cardiomyocyte. For example, high con- centrations of Ca may be expected in the sarcoplasmic * Corresponding author. Fax: +1 802 656 0747. E-mail address: palmer@physiology.med.uvm.edu (B.M. Palmer).