Stimulatory pathways of the Calcium-sensing receptor on acid secretion in freshly isolated human gastric glands

Cell Physiol Biochem. 2007;19(1-4):33-42. doi: 10.1159/000099190.

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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Calcium / pharmacology
  • Enzyme Activation
  • Female
  • GTP-Binding Proteins / metabolism
  • Gadolinium / pharmacology
  • Gastric Acid / metabolism*
  • Gastric Mucosa / cytology
  • Gastric Mucosa / metabolism*
  • H(+)-K(+)-Exchanging ATPase / metabolism*
  • Humans
  • Male
  • Middle Aged
  • Mitogen-Activated Protein Kinase 3 / metabolism
  • Models, Biological
  • Protein Kinase C / genetics
  • Protein Kinase C / metabolism
  • Proton Pumps / physiology
  • Receptors, Calcium-Sensing / metabolism*
  • Receptors, Calcium-Sensing / physiology
  • Signal Transduction*
  • Type C Phospholipases / metabolism

Substances

  • Proton Pumps
  • Receptors, Calcium-Sensing
  • Gadolinium
  • Protein Kinase C
  • Mitogen-Activated Protein Kinase 3
  • Type C Phospholipases
  • GTP-Binding Proteins
  • H(+)-K(+)-Exchanging ATPase
  • Calcium