Figure 4. Effects of iron deficiency on myocyte geometry, dyadic structure, and Ca²⁺ currents.

(A) Cell length and width measured in cSNARF1-loaded myocytes isolated from hearts (n = 120–140 cells from 4 animals/group) and (B) membrane capacitance measured in voltage-clamped myocytes (n > 15 cells from 4 animals/group). No difference in cell size or surface area were detected in myocytes from iron-deficient animals. (C) Immunofluorescence staining for L-type calcium channel (LCC) protein in permeabilized myocytes. LCCs are found predominantly in T-Tubules, and the staining pattern visualizes the state of sarcolemmal invaginations. No evidence of detubulation is observed in myocytes from iron-deficient mice. Scale bar: 20 μm. Exemplar images are shown. (D) Electron micrograph of isolated ventricular myocytes. Exemplar images are shown from n = 3 animals/group. TT, T-Tubule; jSR, junctional SR; m, mitochondria; z, Z-line. No changes in the dyadic ultrastructure were observed in myocytes from iron-deficient animals. (E) L-type Ca²⁺ current density, measured as a function of holding potential (n > 15 cells from 4 animals/group), by voltage-clamp electrophysiology. No difference in trigger Ca²⁺ current was observed in the 4 experimental groups. See Supplemental Table 1 for details of the number of experimental repeats.