AJP - Gastrointestinal and Liver Physiology, Vol 251, Issue 1 75-G83, Copyright © 1986 by American Physiological Society
Regulation of muscarinic acetylcholine receptors in cultured guinea pig pancreatic acini
S. R. Hootman, M. E. Brown, J. A. Williams and C. D. Logsdon
Regulation of muscarinic receptors in cultured guinea pig pancreatic acini
was investigated by assessing the effects of cholinergic agonists on
binding of [N-methyl-3H]scopolamine [( 3H]NMS) and on amylase release.
Freshly dispersed acini bound [3H]NMS with a Kd of 74 pM and a maximal
binding level (Bmax) of 908 fmol/mg DNA. Carbachol (CCh) stimulated amylase
secretion and inhibited [3H]NMS binding. Incubation of acini for 30 min
with 0.1 mM CCh decreased the subsequent efficacy of CCh in stimulating
amylase release by threefold but had no effect on its potency. In contrast,
amylase release in response to cholecystokinin octapeptide (CCK-8) was not
altered by CCh preincubation. [3H]NMS binding to acini was decreased only
15-20% after 30-min incubation with CCh. However, culture of acini with 0.1
mM CCh decreased [3H]NMS binding by 50% at 3-4 h and by 85-90% at 24 h.
This decrease was attributable primarily to a reduction in Bmax. [3H]NMS
binding also was decreased to a similar extent by the cholinergic agonists
bethanechol and methacholine but not by other secretagogues. The decrease
in antagonist binding induced by CCh was dose dependent, with the IC50, 5.8
microM, approximating the EC50 for amylase release, 4.3 microM. Culture of
acini for 24 h with CCh abolished subsequent amylase release in response to
CCh but not to CCK-8. When CCh was removed from the culture medium after 24
h and acini recultured in its absence, [3H]NMS binding increased with a
half-time for recovery of 20-24 h; this recovery was blocked by
cycloheximide.(ABSTRACT TRUNCATED AT 250 WORDS)
