title: Stimulatory pathways of the Calcium-sensing receptor on acid secretion in freshly isolated human gastric glands.
abstract: Gastric acid secretion is not only stimulated via the classical known neuronal and hormonal pathways but also by the Ca(2+)-Sensing Receptor (CaSR) located at the basolateral membrane of the acid-secretory gastric parietal cell. Stimulation of CaSR with divalent cations or the potent agonist Gd(3+) leads to activation of the H(+)/K(+)-ATPase and subsequently to gastric acid secretion. Here we investigated the intracellular mechanism(s) mediating the effects of the CaSR on H(+)/K(+)-ATPase activity in freshly isolated human gastric glands. Inhibition of heterotrimeric G-proteins (G(i) and G(o)) with pertussis toxin during stimulation of the CaSR with Gd(3+) only partly reduced the observed stimulatory effect. A similar effect was observed with the PLC inhibitor U73122. The reduction of the H(+)/K(+)-ATPase activity measured after incubation of gastric glands with BAPTA-AM, a chelator of intracellular Ca(2+), showed that intracellular Ca(2+) plays an important role in the signalling cascade. TMB-8, a ER Ca(2+)store release inhibitor, prevented the stimulation of H(+)/K(+)-ATPase activity. Also verapamil, an inhibitor of L-type Ca(2+)-channels reduced stimulation suggesting that both the release of intracellular Ca(2+) from the ER as well as Ca(2+) influx into the cell are involved in CaSR-mediated H(+)/K(+)-ATPase activation. Chelerythrine, a general inhibitor of protein kinase C, and Go 6976 which selectively inhibits Ca(2+)-dependent PKC(alpha) and PKC(betaI)-isozymes completely abolished the stimulatory effect of Gd(3+). In contrast, Ro 31-8220, a selective inhibitor of the Ca(2+)-independent PKCepsilon and PKC-delta isoforms reduced the stimulatory effect of Gd(3+) only about 60 %. On the other hand, activation of PKC with DOG led to an activation of H(+)/K(+)-ATPase activity which was only about 60 % of the effect observed with Gd(3+). Incubation of the parietal cells with PD 098059 to inhibit ERK1/2 MAP-kinases showed a significant reduction of the Gd(3+) effect. Thus, in the human gastric parietal cell the CaSR is coupled to pertussis toxin sensitive heterotrimeric G-Proteins and requires calcium to enhance the activity of the proton-pump. PLC, ERK 1/2 MAP-kinases as well as Ca(2+) dependent and Ca(2+)-independent PKC isoforms are part of the down-stream signalling cascade.
authors.affiliation: Institute of Physiology and Zurich Center for Integrative Human Physiology (ZIHP), University of Zurich, Zürich, Schweiz.
authors.forename: Christine
authors.initials: C
authors.lastname: Remy
authors.forename: Philipp
authors.initials: P
authors.lastname: Kirchhoff
authors.forename: Patricia
authors.initials: P
authors.lastname: Hafner
authors.forename: Stephanie M
authors.initials: SM
authors.lastname: Busque
authors.forename: Markus K
authors.initials: MK
authors.lastname: Müeller
authors.forename: John P
authors.initials: JP
authors.lastname: Geibel
authors.forename: Carsten A
authors.initials: CA
authors.lastname: Wagner
mesh_terms: D000328:Adult; D002118:Calcium / Q000494:pharmacology; D004789:Enzyme Activation; D005260:Female; D019204:GTP-Binding Proteins / Q000378:metabolism; D005682:Gadolinium / Q000494:pharmacology; D005744:Gastric Acid / Q000378:metabolism*; D005753:Gastric Mucosa / Q000166:cytology / Q000378:metabolism*; D017506:H(+)-K(+)-Exchanging ATPase / Q000378:metabolism*; D006801:Humans; D008297:Male; D008875:Middle Aged; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D008954:Models, Biological; D011493:Protein Kinase C / Q000235:genetics / Q000378:metabolism; D017494:Proton Pumps / Q000502:physiology; D044169:Receptors, Calcium-Sensing / Q000378:metabolism* / Q000502:physiology; D015398:Signal Transduction; D010738:Type C Phospholipases / Q000378:metabolism
chemical_list: D017494:Proton Pumps; D044169:Receptors, Calcium-Sensing; D005682:Gadolinium; D011493:Protein Kinase C; D048052:Mitogen-Activated Protein Kinase 3; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins; D017506:H(+)-K(+)-Exchanging ATPase; D002118:Calcium