Biphasic kinetics of inositol 1,4,5-trisphosphate accumulation in gastrin-stimulated parietal cells. Effects of pertussis toxin and extracellular calcium.
The effects of Pertussis toxin (PTx) and extracellular Ca2+ were investigated on gastrin-induced Ins(1,4,5)P3 mass level in isolated gastric parietal cells. Basal Ins(1,4,5)P3 content was 5.48 +/- 0.49 pmol/500,000 cells. Gastrin (10 nM) induced a rapid increase in Ins(1,4,5)P3 content which was maximal after 15 s and corresponded to 2-2.5-fold basal level; this Ins(1,4,5)P3 content then decreased within 30 s. After a longer time of gastrin exposure (greater than 1 min), a sustained and unexpected increase in Ins(1,4,5)P3 accumulation was observed which was maximal at 7.5 min (corresponding to 2.3-2.8-fold basal value) and slightly decreased thereafter. PTx treatment of cells (200 ng/ml) for 3 h or removal of extracellular Ca2+ did not affect the rapid rise, but drastically reduced the sustained increase in Ins(1,4,5)P3 content (60-100% inhibition); this inhibition was not evident after 10 min of hormone stimulation. Furthermore, diltiazem, a Ca2+ channel blocker, led to a similar inhibition of the sustained increase. We concluded that: (i) gastrin induced a rapid increase in Ins(1,4,5)P3 content via a mechanism insensitive to PTx and to extracellular Ca2+, and (ii) gastrin induced a sustained increase in Ins(1,4,5)P3 level via a mechanism sensitive to PTx and to extracellular Ca2+. Even though the rapid rise in Ins(1,4,5)P3 content may be involved in the intracellular Ca2+ mobilization occurring after the first seconds of hormone stimulation, the physiological role of the sustained Ins(1,4,5)P3 increased level remains to be elucidated.
Roche
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S
Laboratoire de Biochimie des Membranes, CNRS UPR-8402-INSERM U-249, Faculté de Pharmacie, France.
Gusdinar
T
T
Bali
J P
JP
Magous
R
R
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002478:Cells, Cultured; D004110:Diltiazem / Q000494:pharmacology; D005755:Gastrins / Q000502:physiology*; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D007700:Kinetics; D010295:Parietal Cells, Gastric / Q000378:metabolism*; D037342:Pertussis Toxin; D011817:Rabbits; D010566:Virulence Factors, Bordetella / Q000494:pharmacology*
D005755:Gastrins; D010566:Virulence Factors, Bordetella; D015544:Inositol 1,4,5-Trisphosphate; D037342:Pertussis Toxin; D004110:Diltiazem; D002118:Calcium