Beta-adrenergic regulation of cholecystokinin secretion in STC-1 cells.
Previously, it has been shown that an increase in adenosine 3',5'-cyclic monophosphate (cAMP) levels stimulates intestinal secretion of cholecystokinin (CCK); however, the mechanisms for increasing intracellular cAMP levels are not known. Using the CCK-secreting intestinal cell line, STC-1, we evaluated whether beta-adrenergic receptors (beta-ARs) might be present on STC-1 cells and whether they stimulated CCK release through increases in cAMP. Photoaffinity labeling of beta-ARs from solubilized STC-1 cell membranes revealed photoincorporation of the agonist [125I]iodocyanopindolol into an approximately 75-kDa band. Addition of the beta-AR agonist, isoproterenol, in the presence of 3-isobutyl-1-methylxanthine, produced a concentration-dependent increase in both cAMP levels and CCK release. Blockade of beta 1- and/or beta 2-ARs significantly inhibited isoproterenol-stimulated increases in cAMP production and CCK release. With the use of fura 2-loaded cells to measure changes in intracellular Ca2+ concentration ([Ca2+]i), isoproterenol stimulation was found to increase cytosolic Ca2+ levels. To evaluate whether this increase in [Ca2+]i was due to release of Ca2+ or influx of Ca2+, cells were treated with the L-type calcium channel blocker, diltiazem, which inhibited isoproterenol-stimulated CCK secretion. Furthermore, in patch-clamp studies with inside-out membrane patches, addition of the catalytic subunit of protein kinase A activated diltiazem-sensitive Ca2+ channels. It is concluded that beta-ARs are present on STC-1 cells and are coupled to the production of cAMP, which may increase CCK release through a calcium-dependent process.
Scott
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Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710, USA.
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Capel
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Basavappa
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Mangel
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Gettys
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Liddle
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D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000345:Affinity Labels; D000818:Animals; D002118:Calcium / Q000502:physiology; D002766:Cholecystokinin / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D051379:Mice; D011943:Receptors, Adrenergic, beta / Q000502:physiology*; D014407:Tumor Cells, Cultured
D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D000345:Affinity Labels; D011943:Receptors, Adrenergic, beta; D002766:Cholecystokinin; D000242:Cyclic AMP; D002118:Calcium