Abstract
In order to develop a method to study secretion of
insulin at a cellular level, we observed endocrine
islet cells in the rat pancreas using a video-enhanced
contrast differential interference contrast microscope.
At a very high magnification (×10,000), islet
cells were easily distinguished from acinar cells
by their differences in appearance, and individual
secretory granules of the islet cells were definitely
resolved. When the concentration of glucose in the
bathing medium was raised from 1.5 mM to 15 mM,
many secretory granules showed abrupt light intensity
changes and disappeared sequentially (degranulation).
The cells that responded to glucose were
immunopositive when fixed in mid-response and
stained with anti-insulin antibody. These results
indicate that the responses induced by glucose stimulation
reflect the secretory activity of insulincontaining
β-cells. Secretagogues of insulin, tolbutamide
(100 μM) and A23187 (1 μM), induced even
stronger responses than glucose. Direct visualization
of these quantal responses in real time in
pancreatic tissues will be very promising for studies
of dynamics of insulin secretion.
