Calcium-induced calcium release drives contraction in cardiomyocytes. Located on the sarcoplasmic reticulum, ryanodine receptors (RyR) are responsible for the release of intracellular calcium stores. It has recently become apparent that the size and shape of RyR cluster may affect the functionality of that cluster, along with the relative distance to neighbouring clusters. Here, we compared the distribution of RyRs in the atria and ventricle.

Isolated sheep ventricular and atrial myocytes were labelled with a monoclonal mouse antibody against RyR. A secondary antibody of Alexa 647 allowed image acquisition using the Nikon super resolution N-STORM 4.0 microscope. We used photo-switchable fluorescent labels and acquired blinks over 10 000 frames in order to resolve RyR clusters. In both the atria and ventricle, the RyRs were predominantly arranged along the z-lines with few longitudinal projections. However, we found distinct differences in the size and distance between these clusters. The RyRs in the ventricle are arranged into distinct clusters. In the atria, on the other hand, the RyR are more continuous along the z-line with less obvious cluster formation.

The use of super resolution allowed in-depth examination of the RyR in both the atria and ventricle. Our data suggests that there are chamber differences with respect to RyR distribution. This may account for the differences in calcium release mechanisms.

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Abstract 231 Figure 1

Typical images of ryanodine receptors in sheep ventricle (A) and atria (B) obtained via super resolution STORM (stoichiometric optical reconstruction microscopy) imaging. Scale bar: 0.5 µm.