Expression of functional GABAA receptors in cholecystokinin-secreting gut neuroendocrine murine STC-1 cells.
1. Gastrointestinal neuroendocrine (NE) cells synthesize, store and secrete gamma-aminobutyric acid (GABA). Recently, an autocrine-paracrine function of GABA has been proposed for secretion from NE cells. 2. To search for functional GABAA receptors in NE gut cells, we performed whole-cell and perforated-patch-clamp studies in the intestinal cholecystokinin (CCK)-secreting NE cell line STC-1. 3. Application of GABA evoked currents in STC-1 cells. These effects were mimicked by muscimol, an agonist of GABAA receptors, and blocked by picrotoxin or bicuculline, antagonists of GABAA receptors. The GABA- or muscimol-activated currents reversed near 0 mV, which under the recording conditions used was consistent with the activation of the GABAA receptor-Cl- channel complex. 4. In contrast to the effect on most neurons, GABA as well as muscimol led to a (reversible) depolarization of the membrane potential of STC-1 cells. Membrane depolarization in turn activated voltage-gated Ca2+ channels and increased intracellular Ca2+ concentrations in STC-1 cells. 5. In accordance with the observed membrane depolarization and activation of voltage-gated Ca2+ channels, both GABA and muscimol stimulated Ca2+-dependent CCK release. In contrast, bicuculline inhibited the GABA-induced secretion of CCK. 6. Using the reverse transcription-polymerase chain reaction (RT-PCR), mRNA of the GABAA receptor subunits alpha2, alpha3, alpha5, beta1, beta3 and delta could be detected in STC-1 cells. 7. In summary, we have shown that the CCK-secreting gut NE cell line STC-1 expresses functional GABAA receptors and that GABA stimulates CCK release. Thus, GABA is involved in the fine tuning of CCK secretion from the gut NE cell line STC-1.
Glassmeier
G
G
Department of Gastroenterology, Universitatsklinikum Benjamin Franklin, Freie Universitat Berlin, Germany.
Herzig
K H
KH
Höpfner
M
M
Lemmer
K
K
Jansen
A
A
Scherubl
H
H
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D018118:Chloride Channels / Q000187:drug effects; D002766:Cholecystokinin / Q000096:biosynthesis*; D004558:Electric Stimulation; D004594:Electrophysiology; D015640:Ion Channel Gating / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D009490:Neurosecretory Systems / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000096:biosynthesis; D011963:Receptors, GABA-A / Q000096:biosynthesis*; D013050:Spectrometry, Fluorescence; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D018118:Chloride Channels; D012333:RNA, Messenger; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid; D002766:Cholecystokinin; D002118:Calcium