scholarly journals The Expression and Role of Hyperpolarization-Activated and Cyclic Nucleotide-Gated Channels in Endocrine Anterior Pituitary Cells

2012 ◽  
Vol 26 (1) ◽  
pp. 153-164 ◽  
Author(s):  
Karla Kretschmannova ◽  
Marek Kucka ◽  
Arturo E. Gonzalez-Iglesias ◽  
Stanko S. Stojilkovic
Keyword(s):  
Cell Membrane ◽  
Electrical Activity ◽  
Adenylyl Cyclase ◽  
Phospholipase C ◽  
Cyclic Nucleotide ◽  
Anterior Pituitary ◽  
Hcn Channels ◽  
Pituitary Cells ◽  
Stimulation Of

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 GH3 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.

Stimulation of Ca(2+)-dependent exocytosis of the sperm acrosome by cAMP acting downstream of phospholipase A2

Reproduction ◽  
2000 ◽  
pp. 57-68 ◽  
Author(s):  
J Garde ◽  
ER Roldan
Keyword(s):  
Arachidonic Acid ◽  
Phospholipase A2 ◽  
Phospholipase C ◽  
Phosphodiesterase Inhibitors ◽  
Dibutyryl Camp ◽  
Camp Phosphodiesterase ◽  
Ram Sperm ◽  
Camp Formation ◽  
Stimulation Of

Spermatozoa undergo exocytosis in response to agonists that induce Ca2+ influx and, in turn, activation of phosphoinositidase C, phospholipase C, phospholipase A2, and cAMP formation. Since the role of cAMP downstream of Ca2+ influx is unknown, this study investigated whether cAMP modulates phospholipase C or phospholipase A2 using a ram sperm model stimulated with A23187 and Ca2+. Exposure to dibutyryl-cAMP, phosphodiesterase inhibitors or forskolin resulted in enhancement of exocytosis. However, the effect was not due to stimulation of phospholipase C or phospholipase A2: in spermatozoa prelabelled with [3H]palmitic acid or [14C]arachidonic acid, these reagents did not enhance [3H]diacylglycerol formation or [14C]arachidonic acid release. Spermatozoa were treated with the phospholipase A2 inhibitor aristolochic acid, and dibutyryl-cAMP to test whether cAMP acts downstream of phospholipase A2. Under these conditions, exocytosis did not occur in response to A23187 and Ca2+. However, inclusion of dibutyryl-cAMP and the phospholipase A2 metabolite lysophosphatidylcholine did result in exocytosis (at an extent similar to that seen when cells were treated with A23187/Ca2+ and without the inhibitor). Inclusion of lysophosphatidylcholine alone, without dibutyryl-cAMP, enhanced exocytosis to a lesser extent, demonstrating that cAMP requires a phospholipase A2 metabolite to stimulate the final stages of exocytosis. These results indicate that cAMP may act downstream of phospholipase A2, exerting a regulatory role in the exocytosis triggered by physiological agonists.

scholarly journals Spontaneous and Receptor-Controlled Soluble Guanylyl Cyclase Activity in Anterior Pituitary Cells

2001 ◽  
Vol 15 (6) ◽  
pp. 1010-1022 ◽  
Author(s):  
Tatjana S. Kostic ◽  
Silvana A. Andric ◽  
Stanko S. Stojilkovic
Keyword(s):  
Adenylyl Cyclase ◽  
Guanylyl Cyclase ◽  
Anterior Pituitary ◽  
Soluble Guanylyl Cyclase ◽  
Gh3 Cells ◽  
Pituitary Cells ◽  
Cgmp Production ◽  
Pituitary Tissue ◽  
Anterior Pituitary Cells ◽  
Inducible Nos

Abstract Nitric oxide (NO)-dependent soluble guanylyl cyclase (sGC) is operative in mammalian cells, but its presence and the role in cGMP production in pituitary cells have been incompletely characterized. Here we show that sGC is expressed in pituitary tissue and dispersed cells, enriched lactotrophs and somatotrophs, and GH3 immortalized cells, and that this enzyme is exclusively responsible for cGMP production in unstimulated cells. Basal sGC activity was partially dependent on voltage-gated calcium influx, and both calcium-sensitive NO synthases (NOS), neuronal and endothelial, were expressed in pituitary tissue and mixed cells, enriched lactotrophs and somatotrophs, and GH3 cells. Calcium-independent inducible NOS was transiently expressed in cultured lactotrophs and somatotrophs after the dispersion of cells, but not in GH3 cells and pituitary tissue. This enzyme participated in the control of basal sGC activity in cultured pituitary cells. The overexpression of inducible NOS by lipopolysaccharide + interferon-γ further increased NO and cGMP levels, and the majority of de novo produced cGMP was rapidly released. Addition of an NO donor to perifused pituitary cells also led to a rapid cGMP release. Calcium-mobilizing agonists TRH and GnRH slightly increased basal cGMP production, but only when added in high concentrations. In contrast, adenylyl cyclase agonists GHRH and CRF induced a robust increase in cGMP production, with EC50s in the physiological concentration range. As in cells overexpressing inducible NOS, the stimulatory action of GHRH and CRF was preserved in cells bathed in calcium-deficient medium, but was not associated with a measurable increase in NO production. These results indicate that sGC is present in secretory anterior pituitary cells and is regulated in an NO-dependent manner through constitutively expressed neuronal and endothelial NOS and transiently expressed inducible NOS, as well as independently of NO by adenylyl cyclase coupled-receptors.

Modification of cardiac β-adrenoceptor mechanisms by H2O2

1998 ◽  
Vol 274 (2) ◽  
pp. H416-H423 ◽  
Author(s):  
Sujata Persad ◽  
Heinz Rupp ◽  
Rashi Jindal ◽  
Jugpal Arneja ◽  
Naranjan S. Dhalla
Keyword(s):  
Oxidative Stress ◽  
Signal Transduction ◽  
Adenylyl Cyclase ◽  
G Proteins ◽  
Cardiac Dysfunction ◽  
Biochemical Parameters ◽  
Adenylyl Cyclase Activity ◽  
High Concentrations ◽  
Stimulation Of

From the role of oxidative stress in cardiac dysfunction, we investigated the effect of H2O2, an activated species of oxygen, on β-adrenoceptors, G proteins, and adenylyl cyclase activities. Rat heart membranes were incubated with different concentrations of H2O2before the biochemical parameters were measured. Both the affinity and density of β1-adrenoceptors were decreased, whereas the density of the β2-adrenoceptors was decreased and the affinity was increased by 1 mM H2O2. Time- and concentration-dependent biphasic changes in adenylyl cyclase activities in the absence or presence of isoproterenol were observed when membranes were incubated with H2O2; however, activation of the enzyme by isoproterenol was increased or unaltered. The adenylyl cyclase activities in the absence or presence of forskolin, NaF, and Gpp(NH)p were depressed by H2O2. Catalase alone or in combination with mannitol was able to significantly decrease the magnitude of alterations due to H2O2. The cholera toxin-stimulated adenylyl cyclase activity and ADP ribose labeling of Gs proteins were decreased by treatment with 1 mM H2O2, whereas Gi protein activities, as reflected by pertussis toxin-stimulation of adenylyl cyclase and ADP ribosylation, were unaltered. The Gs and Gi protein immunoreactivities, estimated by labeling with respective antibodies, indicate a decrease in binding to the 45-kDa band of Gs protein, whereas no change in the binding of antibodies to the 52-kDa band of Gs protein or the 40-kDa subunit of Gi protein was evident when the membranes were treated with 1 mM H2O2. These results suggest that H2O2in high concentrations may attenuate the β-adrenoceptor-linked signal transduction in the heart by changing the functions of Gs proteins and the catalytic subunit of the adenylyl cyclase enzyme.

Thyrotropin-Releasing Hormone Gene Expression in Cultured Anterior Pituitary Cells: Role of Gender

1995 ◽  
Vol 61 (1) ◽  
pp. 77-84 ◽  
Author(s):  
Thomas O. Bruhn ◽  
Jan M.M. Rondeel ◽  
Thomas G. Bolduc ◽  
Ivor M.D. Jackson
Keyword(s):  
Gene Expression ◽  
Anterior Pituitary ◽  
Thyrotropin Releasing Hormone ◽  
Pituitary Cells ◽  
Releasing Hormone ◽  
Anterior Pituitary Cells

Involvement of phospholipase C in endothelin 1–induced stimulation of Ca++ channels and basilar artery contraction in rabbits

2006 ◽  
Vol 105 (2) ◽  
pp. 288-293 ◽  
Author(s):  
Yoshifumi Kawanabe ◽  
Tomoh Masaki ◽  
Nobuo Hashimoto
Keyword(s):  
Phospholipase C ◽  
Essential Role ◽  
Ca Channels ◽  
Endothelin 1 ◽  
Nonselective Cation Channels ◽  
Basilar Arteries ◽  
Independent Cascade ◽  
Dependent Pathway ◽  
Stimulation Of

Object Endothelin 1 (ET-1) is a major cause of cerebral vasospasm after subarachnoid hemorrhage (SAH), and extracellular Ca++ influx plays an essential role in ET-1–induced vasospasm. The authors recently demonstrated that ET-1 activates two types of Ca++-permeable nonselective cation channels (designated NSCC-1 and NSCC-2) and a store-operated Ca++ channel (SOCC) in vascular smooth-muscle cells located in the basilar arteries (BAs) of rabbits. In the present study, they investigate the effects of phospholipase C (PLC) on ET-1–induced activation of these Ca++ channels and BA contraction by using the PLC inhibitor U73122. Methods To determine which Ca++ channels are activated via a PLC-dependent pathway, these investigators monitored the intracellular free Ca++ concentration ([Ca++]i). The role of PLC in ET-1–induced vascular contraction was examined by performing a tension study of rabbit BA rings. The U73122 inhibited the ET-1–induced transient increase in [Ca++]i, which resulted from mobilization of Ca++; from the intracellular store. Phospholipase C also inhibited ET-1–induced extracellular Ca++ influx through the SOCC and NSCC-2, but not through the NSCC-1. The U73122 inhibited the ET-1–induced contraction of the rabbit BA rings, which depended on extracellular Ca++ influx through the SOCC and NSCC-2. Conclusions These results indicate the following. 1) The SOCC and NSCC-2 are stimulated by ET-1 via a PLC-dependent cascade whereas NSCC-1 is stimulated via a PLC-independent cascade. 2) The PLC is involved in the ET-1–induced contraction of rabbit BA rings, which depends on extracellular Ca++ influx through the SOCC and NSCC-2.

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