[Ca.sup.2+] signaling in porcine duodenal glands by muscarinic receptor activation

Teraoka, Hiroki, Yutaka Maruyama, Kazushige Takehana, Toshihiko Iwanaga, Takeo Hiraga, Shoichi Fujita, and Toshio Ohta. [Ca.sup.2+] signaling in porcine duodenal glands by muscarinic receptor activation. Am J Physiol Gastrointest Liver Physiol 280: G729-G737, 2001.--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 [Ca.sup.2+] concentration ([[[Ca.sup.2+]].sub.i]) and on membrane currents with fura 2 fluorometry and the patch clamp technique. ACh caused a transient increase in [[[Ca.sup.2+]].sub.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 [M.sub.3] subtype far exceeded that for either [M.sub.1] or [M.sub.2] as revealed by real-time quantitative PCR and in situ hybridization. The rise in [[[Ca.sup.2+]].sub.i] evoked by ACh was largely inhibited by thapsigargin but slightly affected by extracellular [Ca.sup.2+] deprivation. Caffeine had no effect on [[[Ca.sup.2+]].sub.i]. ACh elicited [Ca.sup.2+]-dependent [K.sup.+] currents, a finding similar to the response to inositol 1,4,5,-trisphosphate applied intracellularly. These results suggest the presence of [M.sub.3] receptors linked to [Ca.sup.2+] release in porcine duodenal glands. Brunner's gland; calcium-induced calcium release; inositol 1,4,5-trisphosphate-induced calcium release; mucus; secretion