Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.13.12.5 (aequorin)
 1,451 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In isolated chief cells from the guinea pig, cholecystokinin (10 nM) and a high concentration of ionomycin each caused a biphasic pattern of pepsinogen secretion. The initial fast response to cholecystokinin was not dependent on medium Ca2+ ans was mimicked by low concentration of ionomycin (100 nM). Inositol 1,4,5-trisphosphate caused a similar fast release from permeabilized cells. The slow component of release was dependent on medium Ca2+, however, and was mimicked by the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) (100 nM) or the diacylglycerol analogue 1-oleoyl-2-acetylglycerol (OAG) (100 microM). Ionomycin (100 nM) and TPA (and/or OAG), when applied together, reproduced the biphasic pattern of pepsinogen secretion, suggesting that the signalling pathways utilized by both types of agonist contribute to the response evoked by cholecystokinin-hormone stimulation. Both fura-2 and aequorin were used to monitor changes of intracellular Ca2+. Three pathways were found to contribute to the Ca2+ transient. A rapid release of Ca2+ from intracellular store(s), a rapid Ca2+ entry from the extracellular space, and a more sustained Ca2+ entry from the extracellular space. Cholecystokinin induced a rapid increase in cytoplasmic Ca2+ ([Ca2+]i) as estimated with fura-2 and aequorin. This rise was reduced but not abolished upon removal of extracellular Ca2+, suggesting that both Ca2+ entry from the extracellular space and Ca2+ mobilization from the intracellular store(s) contribute to the initial, fast component of the Ca2+ transient. A second, more sustained component of the Ca2+ transient induced by cholecystokinin was abolished by lanthanum. TPA and OAG induced a biphasic Ca2+ transient that could be detected only with aequorin. The late, sustained component of this response was again abolished by lanthanum as well as by removal of extracellular Ca2+. It appears that the late component of the Ca2+ transient is dependent on Ca2+ influx from the extracellular space and is too localized to be detected by fura-2. Prestimulation of cells with TPA or OAG prevented the aequorin transient caused by cholecystokinin and vice versa, suggesting that TPA, OAG and cholecystokinin activate the same pathways of Ca2+ entry into the cytosol from the intracellular store(s) or the extracellular space. The stimulation-sensitive Ca2+ pool was examined with electron probe X-ray microanalysis. It appears to be restricted to an area enriched in secretory granules or peripheral endoplasmic reticulum just beneath the apical plasma membrane and in close association with the microtubular-microfilamentous system.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:A role for Ca2+ in mediating hormone-induced biphasic pepsinogen secretion from the chief cell determined by luminescent and fluorescent probes and X-ray microprobe. 296 92

Porcine ileal polypeptide, an enterooxyntin isolated from distal small intestinal mucosal epithelium, has been observed to stimulate gastric acid secretion in vivo as well as in vitro (Wider, M.D. et al. (1984) Endocrinology 115, 1484-1491, Wider M.D. et al. (1986) Endocrinology 118, 1546-1550). We report here that porcine ileal polypeptide stimulates both acid (aminopyrine accumulation) and pepsinogen secretion in isolated, enriched populations of guinea pig parietal and chief cells in a dose-dependent manner. Further, 10(-9) M porcine ileal polypeptide caused an increase in cytoplasmic Ca2+ concentration in both parietal and chief cells similar in magnitude to that observed with gastrin-17 (10(-8) M) (as measured by both fura-2 and aequorin) and cholecystokinin octapeptide (CCK-OP) (10(-8) M), respectively. Porcine ileal polypeptide has been observed to cause no stimulation of cAMP production in gastric glands from guinea pigs (Gespach, C., personal communication) nor is there any effect of medium Ca2+ depletion on acid production observed with guinea pig gastric mucosal sections. It is concluded that porcine ileal polypeptide, at concentrations similar to circulating levels observed in plasma of normal pigs (5 x 10(-9) M), acts directly on the parietal and chief cells to cause the mobilization of intracellular Ca2+ from the stores resulting in acid and pepsinogen secretion. These experiments demonstrate that this peptide is a potent enterooxyntin and chief cell secretagogue which acts via the same signal transduction mechanisms as gastrin and cholecystokinin.
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PMID:Porcine ileal polypeptide causes an increase in cytoplasmic Ca2+ in both parietal and chief cells resulting in acid and pepsinogen secretion. 367 4