This was characterized by a high z-groove index.
The cell surface was flattened and distorted in HF, with a reduction in the z-groove index.
In all conditions studied so far, changes to the z-groove index are associated with dysfunctional CICR.
To quantify the data obtained during scanning we introduced an index of the completeness of the Z grooves on the surface of cardiomyocytes (Z-groove index).
Similarly, HF resulted in the loss of surface structures and a reduction in Z-groove index (0.57±0.01 versus 0.45±0.02 in control versus HF, P<0.001).
On average, human atrial myocytes had a Z-groove index of 0.57±0.02 (n=27), which is similar to that measured in rat RA.
The z-groove index provides a measure of the regularity of the membrane structure, which may or may not impact on the DHPR RyR coupling.
To characterize cardiomyocyte topography, we have introduced the Z-groove index: a ratio of the observed Z-groove length to the total extrapolated Z-groove length (as if they were present throughout the entire surface).
Similarly, the Z-groove index was significantly higher in LA versus RA myocytes (0.66±0.03 versus 0.50±0.03 in LA versus RA, respectively, P<0.001), confirming the presence of more structured myocytes in the LA.
SICM imaging of unloaded cells showed changes on the cardiomyocyte surface and a decrease in the Z-groove index compared with control cells (UN 0.3841±0.02451, n=17 vs. 0.8040±0.03513, n=10; P<0.0001) (Fig. 6 ).
To calculate the Z-groove index, we measured the maximum extent of Z grooves observed on single SICM images and divided this length by the total estimated Z-groove length, as if they extended across the whole surface, guided by the structure of normal SICM images as described previously (30).
