AJP - Gastrointestinal and Liver Physiology, Vol 255, Issue 4 424-G428, Copyright © 1988 by American Physiological Society
Pertussis toxin-sensitive cholinergic inhibition of somatostatin release from canine D-cells
C. B. Chan and A. H. Soll
Center for Ulcer Research and Education, Veterans Administration Wadsworth Medical and Research Services, Los Angeles, California.
Development of an enriched cultured cell system allowed us to investigate
the mechanism of cholinergic inhibition of somatostatin release stimulated
by adenosine 3',5'-cyclic monophosphate (cAMP) and Ca2+-protein kinase
C-dependent pathways of cell activation. After a 24-h culture on rat tail
collagen, D-cells, quantified by immunohistochemistry, were 18-fold
enriched compared with unelutriated dispersed cells. Somatostatin release
from cultured cells was expressed as a percent of the somatostatin released
by a specific stimulus in control cells. Under basal conditions release of
somatostatin was 2.3 +/- 0.6% of the total cell content. Epinephrine (1
microM) and cholecystokinin octapeptide (10 nM) increased somatostatin
release to 6.98 +/- 1.25 and 10.72 +/- 1.64%, respectively. Carbachol (1
microM) completely inhibited somatostatin release stimulated by epinephrine
and reduced cholecystokinin octapeptide-stimulated release to 75% of
control levels. Carbachol inhibition of the response to both epinephrine
and cholecystokinin octapeptide was totally prevented by 5 h of treatment
of the cells with pertussis toxin (300 ng/ml). Somatostatin release in
response to the diterpene forskolin (10 microM), dibutyryl cAMP (300
microM), the phorbol ester beta-phorbol 12-myristate 13-acetate (0.1
microM), and the calcium ionophore A23187 (1 microM) was also inhibited by
carbachol and prevented by pertussis toxin pretreatment. The ADP-ribosylase
inhibitor isonicotinamide (1 mM) selectively blocked the effect of
pertussis toxin without altering other stimulatory or inhibitory responses.
These data are consistent with the view that carbachol inhibits
somatostatin release at guanyl nucleotide-binding protein and/or another
pertussis toxin-sensitive site.
