AJP - Cell Physiology, Vol 245, Issue 1 21-C27, Copyright © 1983 by American Physiological Society
Origin of the decline in pancreatic amylase secretion with time in vitro
J. J. Ho and S. S. Rothman
The release of alpha-amylase (EC 3.2.1.1) into the medium bathing strips of
rabbit pancreas decreased gradually with time in vitro so that after 3 h of
incubation the secretory rate was only 20% of that seen initially. This
decrease was not the result of an intrinsic loss of cellular responsiveness
or viability, because a cholinergic agonist was still able to augment
amylase secretion from the tissue after this incubation period to the same,
or greater, degree than from "fresh" tissue. Rather, the inhibition of
secretion was apparently due to the release of a nondialyzable substance
from the tissue, which appears to be amylase itself. The observations that
led to this conclusion are 1) replacing the bathing medium every 30 min
eliminated the time-dependent decrease in enzyme secretion, 2) this
replacement was ineffective if the tissue was separated from the medium by
a dialysis membrane, and 3) adding an excess of the amylase substrate
glycogen to the medium also prevented the falloff in amylase secretion, the
effect of glycogen presumably being due to the formation of an
enzyme-substrate complex in the medium. These observations are consistent
with other observations that demonstrate that the rate of enzyme secretion
by the pancreas depends on the rate of removal of product from the site of
its secretion [Isenman and Rothman, Proc. Natl. Acad. Sci. USA 74:
4068-4072, 1977; Isenman and Rothman, Science 204: 1212-1215, 1979; Ho and
Rothman, Am. J. Physiol. 242 (Gastrointest. Liver Physiol. 5): G32-G39,
1982].
