Ca2+signaling in porcine duodenal glands by muscarinic receptor activation

Abstract

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 pig, 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 increase was markedly inhibited by atropine or 4-diphenylacetoxy- N-methylpiperidine methiodide but not by hexamethonium, pirenzepine, or methoctramine. The expression of mRNA for the M3subtype far exceeded that for either M1or M2as revealed by real-time quantitative PCR and in situ hybridization. The rise in [Ca2+]ievoked by ACh was largely inhibited by thapsigargin but slightly affected by extracellular Ca2+deprivation. Caffeine had no effect on [Ca2+]i. ACh elicited Ca2+-dependent K+currents, a finding similar to the response to inositol 1,4,5,-trisphosphate applied intracellularly. These results suggest the presence of M3receptors linked to Ca2+release in porcine duodenal glands.