scholarly journals Thapsigargin, but not caffeine, blocks the ability of thyrotropin-releasing hormone to release Ca2+ from an intracellular store in GH4C1 pituitary cells

1990 ◽  
Vol 267 (2) ◽  
pp. 359-364 ◽  
Author(s):  
G J Law ◽  
J A Pachter ◽  
O Thastrup ◽  
M R Hanley ◽  
P S Dannies
Keyword(s):  
Channel Blocker ◽  
Inositol Phosphate ◽  
Cell Types ◽  
Thyrotropin Releasing Hormone ◽  
Pituitary Cells ◽  
Intracellular Store ◽  
Receptor Level ◽  
Releasing Hormone ◽  
Trh Stimulation ◽  
Stimulation Of

Thapsigargin stimulates an increase of cytosolic free Ca2+ concentration [( Ca2+]c) in, and 45Ca2+ efflux from, a clone of GH4C1 pituitary cells. This increase in [Ca2+]c was followed by a lower sustained elevation of [Ca2+]c, which required the presence of extracellular Ca2+, and was not inhibited by a Ca2(+)-channel blocker, nimodipine. Thapsigargin had no effect on inositol phosphate generation. We used thyrotropin-releasing hormone (TRH) to mobilize Ca2+ from an InsP3-sensitive store. Pretreatment with thapsigargin blocked the ability of TRH to cause a transient increase in both [Ca2+]c and 45Ca2+ efflux. The block of TRH-induced Ca2+ mobilization was not caused by a block at the receptor level, because TRH stimulation of InsP3 was not affected by thapsigargin. Rundown of the TRH-releasable store by Ca2(+)-induced Ca2+ release does not appear to account for the action of thapsigargin on the TRH-induced spike in [Ca2+]c, because BAY K 8644, which causes a sustained rise in [Ca2+]c, did not block Ca2+ release caused by TRH. In addition, caffeine, which releases Ca2+ from intracellular stores in other cell types, caused an increase in [Ca2+]c in GH4C1 cells, but had no effect on a subsequent spike in [Ca2+]c induced by TRH or thapsigargin. TRH caused a substantial decrease in the amount of intracellular Ca2+ released by thapsigargin. We conclude that in GH4C1 cells thapsigargin actively discharges an InsP3-releasable pool of Ca2+ and that this mechanism alone causes the block of the TRH-induced increase in [Ca2+]c.

Thyrotropin-releasing hormone stimulates inositol phosphate production in normal anterior pituitary cells and GH3 tumour cells in the presence of lithium

1983 ◽  
Vol 3 (12) ◽  
pp. 1091-1099 ◽  
Author(s):  
John G. Baird ◽  
Pauline R. M. Dobson ◽  
Richard J. H. Wojcikiewicz ◽  
Barry L. Brown
Keyword(s):  
Dose Response ◽  
Anterior Pituitary ◽  
Inositol Phosphate ◽  
Thyrotropin Releasing Hormone ◽  
Pituitary Cells ◽  
Anterior Pituitary Cells ◽  
Trh Stimulation ◽  
Response Profile ◽  
Inositol Phosphate Accumulation ◽  
Stimulation Of

Phosphatidylinositol (Ptd Ins) breakdown in response to thyrotropin-releasing hormone (TRH) was measured after preincubation of both normal rat anterior pituitary cells and GH3 turnout cells with [3H]inositol by the determination of [3H]inositol phosphate accumulation in the presence of lithium (which inhibits myo-inositol phosphatase). The method employed, which was originally developed for use with tissue slices, was adapted for isolated cells in monolayer culture. In GH3 cells, TRH stimulated the breakdown of phosphoinositide in a manner similar to that reported previously using alternative methods. Furthermore, in normal male anterior pituitary cells the dose-response profile for TRH stimulation of inositol phosphate accumulation was found to correlate well with the dose-response profile for TRH stimulation of prolactin secretion. As this response was maintained in the absence of added calcium, the breakdown of phosphoinositide would appear to be implicated as an event preceding calcium mobilization.

scholarly journals Formation of inositol phosphate isomers in GH3 pituitary tumour cells stimulated with thyrotropin-releasing hormone. Acute effects of lithium ions

1987 ◽  
Vol 248 (2) ◽  
pp. 463-470 ◽  
Author(s):  
P J Hughes ◽  
A H Drummond
Keyword(s):  
Inositol Phosphate ◽  
Cell Types ◽  
Pituitary Tumour ◽  
Thyrotropin Releasing Hormone ◽  
Gh3 Cells ◽  
Acute Effects ◽  
Releasing Hormone ◽  
Inositol Phosphate Metabolism ◽  
Trh Stimulation ◽  
Gh3 Cell

With a h.p.l.c. system, the inositol mono-, bis- and tris-phosphate isomers found in [3H]inositol-labelled GH3 cells were resolved and identified. These cells possess at least ten distinct [3H]inositol-containing substances when acid-soluble extracts are analysed by anion-exchange h.p.l.c. These substances were identified by their co-elution with known inositol phosphate standards and, to a limited extent, by examining their chemical structure. Two major inositol monophosphate (InsP) isomers were identified, namely Ins1P and Ins4P, both of which accumulate after stimulation with the hypothalamic releasing factor (TRH) (thyrotropin-releasing hormone). Three inositol bisphosphate (InsP2) isomers were resolved, of which two were positively identified, i.e. Ins(1,4)P2 and Ins(3,4)P2. TRH treatment increases both of these isomers, with Ins(1,4)P2 being produced at a faster rate than Ins(3,4)P2. The third InsP2 isomer has yet to be fully identified, although it is co-eluted with an Ins(4,5)P2 standard. This third InsP2 is also increased after TRH stimulation. In common with other cell types, the GH3 cell contains two inositol trisphosphate (InsP3) isomers: Ins(1,4,5)P3, which accumulates rapidly, and Ins(1,3,4)P3, which is formed more slowly. The latter substance appears simultaneously with its precursor, inositol 1,3,4,5-tetrakisphosphate. We also examined the effects of acute Li+ treatment on the rates of accumulation of these isomers, and demonstrated that Li+ augments TRH-mediated accumulation of Ins1P, Ins4P, Ins(1,4)P2, the presumed Ins(4,5)P2 and Ins(1,3,4)P3. These results suggest that the effects of Li+ on inositol phosphate metabolism are more complex than was originally envisaged, and support work carried out by less sophisticated chromatographic analysis.

scholarly journals Imaging of Endoplasmic Reticulum Ca2+ in the Intact Pituitary Gland of Transgenic Mice Expressing a Low Affinity Ca2+ Indicator

2021 ◽  
Vol 11 ◽  
Author(s):  
Jonathan Rojo-Ruiz ◽  
Paloma Navas-Navarro ◽  
Lucía Nuñez ◽  
Javier García-Sancho ◽  
María Teresa Alonso
Keyword(s):  
Endoplasmic Reticulum ◽  
Pituitary Gland ◽  
Transgenic Mouse ◽  
Calcium Release ◽  
Cell Types ◽  
Thyrotropin Releasing Hormone ◽  
Pituitary Cells ◽  
Releasing Hormone ◽  
Pituitary Glands ◽  
Calcium Induced Calcium Release

The adenohypophysis contains five secretory cell types (somatotrophs, lactotrophs, thyrotrophs, corticotrophs, and gonadotrophs), each secreting a different hormone, and controlled by different hypothalamic releasing hormones (HRHs). Exocytic secretion is regulated by cytosolic Ca2+ signals ([Ca2+]C), which can be generated either by Ca2+ entry through the plasma membrane and/or by Ca2+ release from the endoplasmic reticulum (ER). In addition, Ca2+ entry signals can eventually be amplified by ER release via calcium-induced calcium release (CICR). We have investigated the contribution of ER Ca2+ release to the action of physiological agonists in pituitary gland. Changes of [Ca2+] in the ER ([Ca2+]ER) were measured with the genetically encoded low-affinity Ca2+ sensor GAP3 targeted to the ER. We used a transgenic mouse strain that expressed erGAP3 driven by a ubiquitous promoter. Virtually all the pituitary cells were positive for the sensor. In order to mimick the physiological environment, intact pituitary glands or acute slices from the transgenic mouse were used to image [Ca2+]ER. [Ca2+]C was measured simultaneously with Rhod-2. Luteinizing hormone-releasing hormone (LHRH) or thyrotropin releasing hormone (TRH), two agonists known to elicit intracellular Ca2+ mobilization, provoked robust decreases of [Ca2+]ER and concomitant rises of [Ca2+]C. A smaller fraction of cells responded to thyrotropin releasing hormone (TRH). By contrast, depolarization with high K+ triggered a rise of [Ca2+]C without a decrease of [Ca2+]ER, indicating that the calcium-induced calcium-release (CICR) via ryanodine receptor amplification mechanism is not present in these cells. Our results show the potential of transgenic ER Ca2+ indicators as novel tools to explore intraorganellar Ca2+ dynamics in pituitary gland in situ.

scholarly journals Thyrotropin-releasing hormone-mediated Mn2+ entry in perifused rat anterior pituitary cells

1992 ◽  
Vol 283 (2) ◽  
pp. 507-513 ◽  
Author(s):  
Z J Cui ◽  
P S Dannies
Keyword(s):  
Fluorescence Quenching ◽  
Anterior Pituitary ◽  
Direct Evidence ◽  
Cell Types ◽  
Thyrotropin Releasing Hormone ◽  
Pituitary Cells ◽  
Free Medium ◽  
Releasing Hormone ◽  
Anterior Pituitary Cells ◽  
Do So

Receptor-mediated Ca2+ influx has been shown to exist in several cell types. Thyrotropin-releasing-hormone (TRH)-stimulated Ca2+ entry has also been postulated to exist in rat anterior pituitary cells, but direct evidence has been lacking. We have measured the fluorescence quenching of indo-1 caused by Mn2+ at a Ca(2+)-insensitive wavelength to investigate the actions of TRH on cation entry in dispersed perifused anterior pituitary cells. In indo-1-loaded cells perifused with Ca(2+)-free medium, Mn2+ caused fluorescence quenching in unstimulated cells; TRH caused further quenching. TRH-stimulated Mn2+ entry was transient, and levelled off within a few minutes in the presence of continuous TRH infusion. TRH-stimulated Mn2+ entry was dependent on the concentration of Mn2+ (50 microM-1 mM). TRH (1 microM) caused a larger effect than TRH (10 nM). La3+ and Ni2+ blocked the quenching stimulated by TRH. The rate of basal quenching was not blocked by dopamine, but TRH-stimulated Mn2+ entry was partially blocked by 1 microM-dopamine and almost completely abolished by 10 microM-dopamine. Thapsigargin (1-5 microM), a tumour promotor which depleted intracellular Ca2+ stores, had little effect on Mn2+. F- (20 mM), which activates G-proteins, also had little effect on Mn2+ entry. We conclude that TRH can transiently stimulate Ca2+ entry through a channel than can pass Mn2+ and be inhibited by dopamine. Depleting Ca2+ stores alone is not sufficient to stimulate Ca2+ entry, and so TRH must do so by other mechanisms.

Sign in / Sign up

Export Citation Format

Share Document