Figure 5. Quantitative analysis of
percentage of gap junction population in various size ranges in the
outer cortex versus the inner cortex. While the small-size GJs
(0.01-0.09 μm
2) are mostly populated in both outer and inner
cortices, the large-size GJs (0.8-1.75 μm
2) are only found
in the outer cortical fibers. Importantly, while all small-size GJs in
the outer cortex exhibit loosely-packed connexons (
Figure 2),
the similar small-size GJs in the inner cortex display the
crystalline-packed connexons (
Figure 3D). This result suggests
that (1) small-size newly-formed GJs are gradually developed into
large-size ones during fiber cell differentiation in the outer cortex;
and (2) large-size GJs undergo structural remodeling (such as removal
of cholesterol and re-packing or breakdown of connexons), which results
in a significant reduction in the GJ size during maturation and aging
in the inner cortex.