Mechanism of action of the calcium-sensing receptor in human antral gastrin cells.
OBJECTIVE
Human G cells express the calcium-sensing receptor and respond to extracellular calcium by releasing gastrin. However, the receptor on G cells is insensitive to serum calcium levels. We investigated whether this is a result of differential regulation of signaling pathways compared with parathyroid or calcitonin cells.


METHODS
Gastrin release from primary cultures of human antral epithelial cells enriched for G cells (35%) was measured by radioimmunoassay. G cells were stimulated by increasing extracellular calcium concentration for 1 hour in the presence or absence of antagonists of specific intracellular signaling pathways. Intracellular calcium levels were monitored to evaluate the effect of the antagonists on calcium influx.


RESULTS
Inhibition of phospholipase C decreased calcium-stimulated gastrin release, but blockers of adenylate cyclase, phospholipase A(2), or mitogen-activated protein kinase had no effect. Inhibition of protein kinase C, nonselective cation channels, and phosphodiesterase increased basal and calcium-stimulated gastrin release while decreasing calcium influx. These data were consistent with basally active phosphodiesterase.


CONCLUSIONS
The calcium-sensing receptor on the G cell activates phospholipase C and opens nonselective cation channels, resulting in an influx of extracellular calcium. Protein kinase C isozymes expressed by the G cells play multiple roles regulating both gastrin secretion and phosphodiesterase activity.
Department of Physiology, Faculty of Medicine, 2146 Health Sciences Mall, University of British Columbia, Vancouver V6T 1Z3, Canada. ambuchan@interchange.ubc.ca
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Buchan
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Squires
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Ring
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Meloche
D000225:Adenine / Q000031:analogs & derivatives* / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D017931:DNA Primers; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005753:Gastric Mucosa / Q000201:enzymology; D005755:Gastrins / Q000378:metabolism; D015870:Gene Expression / Q000502:physiology; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D008301:Maleimides / Q000494:pharmacology; D009568:Nitrendipine / Q000494:pharmacology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D011706:Pyloric Antrum / Q000166:cytology* / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D044169:Receptors, Calcium-Sensing; D011956:Receptors, Cell Surface / Q000235:genetics* / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D062367:ortho-Aminobenzoates / Q000494:pharmacology
D002121:Calcium Channel Blockers; D017931:DNA Primers; D004791:Enzyme Inhibitors; D005755:Gastrins; D007211:Indoles; D008301:Maleimides; D010726:Phosphodiesterase Inhibitors; D012333:RNA, Messenger; D044169:Receptors, Calcium-Sensing; D011956:Receptors, Cell Surface; D062367:ortho-Aminobenzoates; C017759:9-(tetrahydro-2-furyl)-adenine; D002110:Caffeine; C001209:fenamic acid; D009568:Nitrendipine; D000242:Cyclic AMP; D011493:Protein Kinase C; D000225:Adenine; C070515:bisindolylmaleimide I; D002118:Calcium