The duodenal glands have been thought to play an important role in defense
against proximal duodenal ulcer; however, the secretory mechanisms of these
glands remain to be determined. In isolated duodenal acinar cells of the p
ig, we investigated the effects of ACh on intracellular Ca2+ concentration
([ Ca2+](i)) and on membrane currents with fura 2 fluorometry and the patch
clamp technique. ACh caused a transient increase in [Ca2+](i), and the inc
rease was markedly inhibited by atropine or 4-diphenylacetoxy-N-methylpiper
idine methiodide but not by hexamethonium, pirenzepine, or methoctramine. T
he expression of mRNA for the M-3 subtype far exceeded that for either M-1
or M-2 as revealed by real-time quantitative PCR and in situ hybridization.
The rise in [Ca2+](i) evoked by ACh was largely inhibited by thapsigargin
but slightly affected by extracellular Ca2+ deprivation. Caffeine had no ef
fect on [Ca2+](i). ACh elicited Ca2+-dependent K+ currents, a finding simil
ar to the response to inositol 1,4,5,-trisphosphate applied intracellularly
. These results suggest the presence of M-3 receptors linked to Ca2+ releas
e in porcine duodenal glands.