Cholecystokinin, carbachol, gastrin, histamine, and forskolin increase [Ca2+]i in gastric glands

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Abstract
The Ca2+-selective fluorescent probe quin 2 was used to measure changes in the concentration of free cytosolic [Ca2+] in isolated rabbit gastric glands. Both carbachol and cholecystokinin octapeptide (CCK-8) were found to increase transiently intracellular Ca2+ concentration, [( Ca2+]i) with maximal increases from approximately 0.15 to 0.5 microM occurring within 4–6 s following secretagogue addition. Increases in [Ca2+]i were dose dependent and inhibited by appropriate antagonists. Prestimulation with either carbachol or CCK-8 effectively prevented increases in [Ca2+]i in response to the other agonist. Acute removal of extracellular Ca2+ slightly reduced the increase in [Ca2+]i that occurred following secretagogue addition but had no effect on pepsinogen secretion. Severe Ca2+ depletion resulted in potent inhibition of the quin 2 signal and suppressed basal pepsinogen release and reduced, but did not totally block, pepsinogen release in response to carbachol and CCK-8. Gastrin stimulation also elevated [Ca2+]i in glands, but this agonist was only 40–50% as effective as CCK-8. The cAMP-dependent agonists histamine and forskolin increased [Ca2+]i to approximately the same degree as gastrin. There was a definite lag in the rise in [Ca2+]i following simulation with histamine and forskolin compared with carbachol and CCK-8, which suggests that additional biochemical events occur between agonist-receptor binding and the rise in [Ca2+]i observed with the cAMP-dependent agonists. Both cAMP-dependent and -independent agonists induced an increase in autofluorescence that was slower than the rise in [Ca2+]i but equally affected by extracellular Ca2+ depletion.

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