  Even within small organs like pancreatic islets, different endocrine cell
types and subtypes form a heterogeneous collective to sense the chemical
composition of the extracellular solution and compute an adequate hormonal
output. Erroneous cellular processing and hormonal output due to challenged
heterogeneity result in various disorders with diabetes mellitus as a flagship
metabolic disease. Here we attempt to address the aforementioned functional
heterogeneity with comparing pairwise cell-cell cross-correlations obtained
from simultaneous measurements of cytosolic calcium responses in hundreds of
islet cells in an optical plane to statistical properties of correlations
predicted by the random matrix theory (RMT). We find that the bulk of the
empirical eigenvalue spectrum is almost completely described by RMT prediction,
however, the deviating eigenvalues that exist below and above RMT spectral
edges suggest that there are local and extended modes driving the correlations.
We show that empirical nearest neighbor spacing of eigenvalues follows
universal RMT properties regardless of glucose stimulation, but that number
variance displays clear separation from RMT prediction and can differentiate
between empirical spectra obtained under non-stimulated and stimulated
conditions. We suggest that RMT approach provides a sensitive tool to assess
the functional cell heterogeneity and its effects on the spatio-temporal
dynamics a collective of beta cells in pancreatic islets in physiological
resting and stimulatory conditions.
