Structural variability of dyads relates to calcium release in rat ventricular myocytes

Figures

• 

  Figure 1. Compact dyads. Electron micrographs selected to illustrate structural variability of the compact type of dyads. Top left: A dyad with the t-tubule tightly surrounded by a flat cisterna containing condensed calsequestrin (long arrow). Numerous RyRs are present in the regular dyadic gap (short arrow). Top right: A dyad containing a t-tubule with budding caveolae-like formations (short arrow). A short section of the flat cisterna (long arrow) closely adheres to the t-tubule membrane. Bottom left: A dyadic microdomain with three t-tubule profiles (*). The narrow cisterna closely adheres to the t-tubule (arrow). Numerous RyRs cross the dyadic gap. Bottom right: A dyad made of 3 t-tubule profiles (*) and a narrow cisterna (long arrow) forms multiple tight dyadic gaps with numerous RyRs (short arrow). Note: The left and the right columns show images taken from control and injured myocardia, respectively, but they represent characteristic dyads of both experimental groups.

• 

  Figure 2. Examples of loose dyads. Electron micrographs selected to illustrate structural variability of the loose type of dyads. Top left: A dyad with a regular t-tubule (*) surrounded by a cisterna filled with homogenous electron-dense material and extending away from the t-tubule (arrows). Top right: Two dyads in a microdomain. The loose dyad between Z-lines has the junctional surface of cisterna partially deflected from the t-tubule (short arrow) and RyRs exposed to cytosol (long arrows). The compact dyad between A-bands of myofibrils contains a part of the longitudinal t-tubule (*) with well adherent cisterna (arrowhead). Bottom left: Two dyads in a microdomain. The dyad indicated by arrows is of the loose type because the junctional membrane of its cisterna deflects (short arrow) and extends (long arrow) from the t-tubule. The dyad made of regular t-tubule profile (*) is of the compact type of dyads. Bottom right: A dyad made of two cisternae (long arrows) and a deformed t-tubule (*). Numerous vesicles are present near the t-tubule (short arrows). Note: The left and the right columns show images taken from control and injured myocardia, respectively, but they represent characteristic…

• 

  Figure 3. Overview of electrophysiological experiments. A and B illustrate a combined whole-cell patch clamp and confocal fluorescence microscopy experiment in a typical CTR (left) and IMY myocyte (right). (A) The voltage stimulus (top traces) and the corresponding calcium current (bottom traces). (B) x-t line-scan confocal fluorescence images of calcium spikes recorded simultaneously with calcium currents in A. The numbered arrowheads point to the positions of the release sites generating calcium spikes shown in C. (C) The time-fluorescence profiles of the spikes indicated in B. Panels A, B, and C have the same time coordinates. (D) The latencies and amplitudes of the recorded calcium spikes from 15 CTR and 17 IMY myocytes. Distribution diagrams of latencies and amplitudes are shown as columns (top and right panels, respectively). Black and red mark CTR and IMY group data, respectively.

• 

  Figure 4. Time courses of integral calcium release fluxes (CRF). Top – Noisy lines - typical time courses of the integral calcium release flux in CTR (left) and IMY (right) myocytes; solid lines - the best-fitted curves of integral CRF (Eq. 2). Dashed and dotted lines – the early and the late components of the best fit curves, respectively. Bottom - The simulated average integral calcium release flux (Eq. 2) with parameters from Table 3. Solid line - the average integral CRF (R = R1 + R2). Dashed and dotted lines - the average early (R1) and late component (R2), respectively.

• 

  Figure 5. Fractions of the unperturbed elements of calcium release in cardiac myocytes. MORPHOL: fractions of compact dyads estimated by morphometry from electron microscopic images (Table 1). ELPHYS: fractions of the early CRF components estimated by fitting records of integral fluorescence signals (Fig. 4). CTR - control myocardium; IMY - injured myocardium. All collected data are shown. Box plots show the 25%, 50% and 75% percentiles; whiskers show 10% and 90% percentile. Solid squares denote the means.