Linkage of [Ca2+]i in single isolated D cells to somatostatin secretion induced by cholecystokinin.
The Ca2+/inositol phospholipid signaling cascade has been implicated in the mechanism by which cholecystokinin (CCK) stimulates gastric somatostatin release, but a direct linkage between intracellular events in gastric D cells and somatostatin secretion has not been established. To address this problem we developed a method for correlating somatostatin release with the measurement of intracellular Ca2+ concentration ([Ca2+]i) in isolated D cells. Resting [Ca2+]i in single D cells was 100 +/- 5.7 nM (means +/- SE, n = 41), and CCK induced a rise in [Ca2+]i in a dose-dependent fashion, producing a maximal stimulatory effect (243 +/- 15% of control, n = 12) at a peptide concentration of 2 x 10(-8) M. The CCK-mediated increase in [Ca2+]i was biphasic, with a rapid, initial transient elevation followed by a sustained plateau. The rise in [Ca2+]i was accompanied by a concomitant increase in release of somatostatin-like immunoreactivity (SLI). Removal of extracellular Ca2+ had no effect on the initial transient elevation in [Ca2+]i induced by CCK but abolished both the sustained plateau in [Ca2+]i and the release of SLI. The selective CCK antagonist L-364, 718 (10(-7) M) inhibited the effects of CCK on both [Ca2+]i and SLI release. The nonspecific Ca2+ channel blocker NiCl2 (10(-3) M) and the L-type Ca2+ channel blocker nifedipine inhibited the sustained rise in [Ca2+]i and the release of SLI but left the initial transient increase in [Ca2+]i unaltered. These results indicate that CCK-stimulated release of SLI from D cells in the gastric fundus is linked to influx of extracellular Ca2+ via L-type Ca2+ channels.
DelValle
J
J
Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor 48109-0682, USA.
Wakasugi
J
J
Takeda
H
H
Yamada
T
T
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002469:Cell Separation; D002478:Cells, Cultured; D002766:Cholecystokinin / Q000494:pharmacology*; D004285:Dogs; D005753:Gastric Mucosa / Q000378:metabolism*; D007425:Intracellular Membranes / Q000378:metabolism; D009994:Osmolar Concentration; D013004:Somatostatin / Q000378:metabolism*; D013270:Stomach / Q000166:cytology
D013004:Somatostatin; D002766:Cholecystokinin; D002118:Calcium