title: The expression and role of hyperpolarization-activated and cyclic nucleotide-gated channels in endocrine anterior pituitary cells.
abstract: Pituitary cells fire action potentials independently of external stimuli, and such spontaneous electrical activity is modulated by a large variety of hypothalamic and intrapituitary agonists. Here, we focused on the potential role of hyperpolarization-activated and cyclic nucleotide-gated (HCN) channels in electrical activity of cultured rat anterior pituitary cells. Quantitative RT-PCR analysis showed higher level of expression of mRNA transcripts for HCN2 and HCN3 subunits and lower expression of HCN1 and HCN4 subunits in these cells. Western immunoblot analysis of lysates from normal and GH(3) immortalized pituitary cells showed bands with appropriate molecular weights for HCN2, HCN3, and HCN4. Electrophysiological experiments showed the presence of a slowly developing hyperpolarization-activated inward current, which was blocked by Cs(+) and ZD7288, in gonadotrophs, thyrotrophs, somatotrophs, and a fraction of lactotrophs, as well as in other unidentified pituitary cell types. Stimulation of adenylyl cyclase and addition of 8-Br-cAMP enhanced this current and depolarized the cell membrane, whereas 8-Br-cGMP did not alter the current and hyperpolarized the cell membrane. Both inhibition of basal adenylyl cyclase activity and stimulation of phospholipase C signaling pathway inhibited this current. Inhibition of HCN channels affected the frequency of firing but did not abolish spontaneous electrical activity. These experiments indicate that cAMP and cGMP have opposite effects on the excitability of endocrine pituitary cells, that basal cAMP production in cultured cells is sufficient to integrate the majority of HCN channels in electrical activity, and that depletion of phosphatidylinositol 4,5-bisphosphate caused by activation of phospholipase C silences them.
authors.affiliation: Section on Cellular Signaling, Program in Developmental Neuroscience, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-4510, USA.
authors.forename: Karla
authors.initials: K
authors.lastname: Kretschmannova
authors.forename: Marek
authors.initials: M
authors.lastname: Kucka
authors.forename: Arturo E
authors.initials: AE
authors.lastname: Gonzalez-Iglesias
authors.forename: Stanko S
authors.initials: SS
authors.lastname: Stojilkovic
mesh_terms: D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000262:Adenylyl Cyclases / Q000096:biosynthesis; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D002586:Cesium / Q000494:pharmacology; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000494:pharmacology; D054815:Cyclic Nucleotide-Gated Cation Channels / Q000096:biosynthesis / Q000378:metabolism*; D055098:Endocrine Cells / Q000378:metabolism*; D005260:Female; D052681:Gonadotrophs / Q000378:metabolism; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D052682:Lactotrophs / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000172:deficiency; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000378:metabolism*; D015221:Potassium Channels / Q000096:biosynthesis / Q000378:metabolism*; D011743:Pyrimidines / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects; D052683:Somatotrophs / Q000378:metabolism; D052684:Thyrotrophs / Q000378:metabolism; D010738:Type C Phospholipases / Q000096:biosynthesis / Q000378:metabolism
chemical_list: D054815:Cyclic Nucleotide-Gated Cation Channels; C578665:HCN1 protein, human; C578667:Hcn1 protein, rat; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D019269:Phosphatidylinositol 4,5-Diphosphate; D015221:Potassium Channels; D011743:Pyrimidines; D012333:RNA, Messenger; C082246:ICI D2788; D002586:Cesium; D015124:8-Bromo Cyclic Adenosine Monophosphate; C016276:8-bromocyclic GMP; D010738:Type C Phospholipases; D000262:Adenylyl Cyclases; D006152:Cyclic GMP