Molecular, pharmacological and functional properties of GABA(A) receptors in anterior pituitary cells.
Anterior pituitary cells express gamma-aminobutyric acid (GABA)-A receptor-channels, but their structure, distribution within the secretory cell types, and nature of action have not been clarified. Here we addressed these questions using cultured anterior pituitary cells from postpubertal female rats and immortalized alphaT3-1 and GH(3) cells. Our results show that mRNAs for all GABA(A) receptor subunits are expressed in pituitary cells and that alpha1/beta1 subunit proteins are present in all secretory cells. In voltage-clamped gramicidin-perforated cells, GABA induced dose-dependent increases in current amplitude that were inhibited by bicuculline and picrotoxin and facilitated by diazepam and zolpidem in a concentration-dependent manner. In intact cells, GABA and the GABA(A) receptor agonist muscimol caused a rapid and transient increase in intracellular calcium, whereas the GABA(B) receptor agonist baclofen was ineffective, suggesting that chloride-mediated depolarization activates voltage-gated calcium channels. Consistent with this finding, RT-PCR analysis indicated high expression of NKCC1, but not KCC2 cation/chloride transporter mRNAs in pituitary cells. Furthermore, the GABA(A) channel reversal potential for chloride ions was positive to the baseline membrane potential in most cells and the activation of ion channels by GABA resulted in depolarization of cells and modulation of spontaneous electrical activity. These results indicate that secretory pituitary cells express functional GABA(A) receptor-channels that are depolarizing.
Zemkova
Hana W
HW
Section on Cellular Signalling, Program in Developmental Neuroscience, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-4510, USA.
Bjelobaba
Ivana
I
Tomic
Melanija
M
Zemkova
Hana
H
Stojilkovic
Stanko S
SS
D000818:Animals; D002478:Cells, Cultured; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D007150:Immunohistochemistry; D010903:Pituitary Gland, Anterior / Q000166:cytology*; D021122:Protein Subunits; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D028021:Sodium-Potassium-Chloride Symporters / Q000235:genetics / Q000378:metabolism; D064506:Solute Carrier Family 12, Member 2; D027981:Symporters / Q000235:genetics / Q000378:metabolism; D000096922:K Cl- Cotransporters
D021122:Protein Subunits; D012333:RNA, Messenger; D011963:Receptors, GABA-A; D028021:Sodium-Potassium-Chloride Symporters; D064506:Solute Carrier Family 12, Member 2; D027981:Symporters; D000096922:K Cl- Cotransporters; C578877:SLC12A2 protein, human; C578879:Slc12a2 protein, rat