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Figure 23. Two cilia in a normal hamster islet cell.
The adjacent islet cells show microvilli. Both cilia
and mircovilli resemble those in ductal/ductular
cells. Some endocrine granules show halo
(arrowhead), mitochondriae (M), Golgi complexes
(G), rough endoplasmic reticulum (RER) and
junctional complexes (arrow). X 4,460. Inset: 9x0
axoneme. Arrows point to plasma membrane.
Similar cilia are present in human islet (Fig. 24).
Figure 24. A cilia was found in a cultured islet cell
of a human. The cells had lost its granules almost
completely and showed atrophy of RER, small
vacuoles and round mitochondriae (upper left and
lower right). TEM, X 4,250.
These cilia are practically indistinguishable from
those of the ductular cells. It is not known at
present whether or not the sinusoidal spaces
between the islet cells are identical or are
communicating with intra-insular tubules seen
under light microscopy. Small (peri-insular)
ductules separated from the islet only by the thin
basal lamina, which surround the islets and
ductules, are directly adjacent to many islets.
Occasional ductules appear to run through or
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indent the islets, but again they are separated by
the basal lamina. Acinar cells, however, may be
directly on islet cells and the basal lamina do not
penetrate between the cells where small
junctional structures resembling desmosomes are
noted.
The significant portion of islets is represented by
β-cells arranged in a cord or ribbon-like fashion,
with the central region of the islets less compact
than the peripheral areas. They have round or
egg-shaped nuclei with moderate chromatin
content and well-defined polygonal or cylindrical,
vesicular, foamy, or light acinophilic granular cytoplasm
in H&E preparation. In the past, the β-cells
could be identified by Gomori's aldehyde fuschin
procedure, which stains the endocrine granules
purple. The α-cells, usually located in the
peripheral region of the islet (abutting a capillary)
can be distinguished from β-cells by their oval or
spindle-shaped nuclei, in which the chromatin
granules are less dense and cytoplasm less
defined than those of the β-cells. In earlier years
their granules could be visualized, somewhat
inconsistently, by Gomori's chrome
alum-hematoxylin-phloxin stain. Silver stains,
such as Bodian and Grimelius, also gave positive
results. By this technique, AIm and Hellman 115
claim to have identified two subtypes of A (α)cells:
the A1 (silver positive) and A2 (silver
negative). In addition to their unsuccessful
attempt to quantitate the number of these
subtypes in the different pancreatic regions, it is
doubtful that the "silver negative" cell is a
derivative of α-cells. They presumably represent
the islet cell precursors, which have been
identified by ourselves and others in several
species (see below). Mallory-Heidenham Azan
allowed identification of the α granules by their
red color, and two distribution patterns of the αcells
(diffusely lying or conglomerate forming
types) have been reported. Gomori's stain
allowed us to identify two to ten α-cells per islet.
Müller 107 reported an alpha/beta ratio of approximately
1:4. All of these stains for α-cell
identification appear to be non-specific. Presently,
monoclonal and/or polyclonal antibodies are