scholarly journals Subsecond and second changes in inositol polyphosphates in GH4C1 cells induced by thyrotropin-releasing hormone

1987 ◽  
Vol 243 (1) ◽  
pp. 305-308 ◽  
Author(s):  
A H Tashjian ◽  
J P Heslop ◽  
M J Berridge
Keyword(s):  
Intracellular Calcium ◽  
Inositol Phosphates ◽  
Thyrotropin Releasing Hormone ◽  
Current View ◽  
Free Calcium ◽  
Calcium Stores ◽  
Pituitary Cells ◽  
Inositol Polyphosphates ◽  
Releasing Hormone ◽  
Polyphosphate Metabolism

It has been demonstrated previously that thyrotropin-releasing hormone (TRH) induces changes in inositol polyphosphates in the GH3 and GH4C1 strains of rat pituitary cells within 2.5-5.0 s. TRH also causes a rapid rise in cytosolic free calcium concentration ([Ca2+]i) in these cells which is due largely to redistribution of cellular calcium stores. Therefore, it has been concluded that TRH acts to release sequestered calcium in these cells via enhanced generation of inositol 1,4,5-trisphosphate [Ins(1,4,5)P3]. If this conclusion were correct, TRH-enhanced accumulation of Ins(1,4,5)P3 should occur at least as rapidly as the increase in [Ca2+]i. We have shown previously that the rise in [Ca2+]i induced by TRH occurs within about 400 ms; thus, it was important to investigate the subsecond time-course of changes in inositol phosphates caused by TRH. Using a rapid mixing device, we have measured changes in inositol polyphosphates on a subsecond time scale in GH4C1 cells prelabelled with myo-[2-3H]inositol. Although TRH did alter inositol polyphosphate metabolism within 500 ms, the changes observed did not reveal a statistically significant increase in Ins(1,4,5)P3 within time intervals of less than 1000 ms. Thus, we have been unable to demonstrate that a TRH-induced rise in Ins(1,4,5)P3 precedes or occurs concomitantly with the rise in [Ca2+]i in GH4C1 cells. Although these results do not disprove the current view that Ins(1,4,5)P3 mediates the action of TRH on intracellular calcium redistribution, we conclude that caution should be exercised in this, and possibly other cell systems, in accepting the dogma that all of the rapid, agonist-induced redistributions of intracellular calcium are mediated by Ins(1,4,5)P3.

scholarly journals Thyrotropin-releasing hormone activates Na+/H+ exchange in rat pituitary cells

1987 ◽  
Vol 242 (2) ◽  
pp. 411-416 ◽  
Author(s):  
T J Hallam ◽  
A H Tashjian
Keyword(s):  
Calcium Ionophore ◽  
Thyrotropin Releasing Hormone ◽  
Free Calcium ◽  
Pituitary Cells ◽  
Ph Indicator ◽  
Ph Change ◽  
Cytosolic Ph ◽  
Releasing Hormone ◽  
Rat Pituitary Cells ◽  
Stimulation Of

The effects of thyrotropin-releasing hormone (TRH) and 12-O-tetradecanoylphorbol 13-acetate (TPA) on cytosolic pH (pHi) were studied on GH4C1 pituitary cells loaded with the fluorescent pH indicator bis(carboxyethyl)carboxyfluorescein (BCECF) and the fluorescent Ca2+ indicator quin2. TRH, which was minimally effective at around 10(-9) M, and TPA, 100 nM, produced very small elevations in pHi of about 0.05 pH units from the normal basal resting pHi of GH4C1 cells of around 7.05. The effects were more marked after acid-loading the cells using 1 micrograms of nigericin/ml. Preincubation with amiloride or replacing the extracellular Na+ with choline+ completely blocked the elevations stimulated by TRH or TPA, consistent with an activation of the Na+/H+ antiport mechanism. The effects were completely independent of the cytoplasmic free calcium concentration ([Ca2+]i). The calcium ionophore ionomycin produced an elevation in [Ca2+]i with no concomitant effect on pHi, and amiloride, although completely inhibiting the pH change stimulated by TRH, failed to affect the initial stimulated [Ca2+]i transient. Although the data are consistent with an elevation in pHi by TRH which is caused by stimulation of a protein kinase C and subsequent activation of the antiporter, the rapidity of the onset of the pHi response to TRH could not be mimicked by a combination of TPA and ionomycin. These results, together with previous findings which show that secretion can be mimicked by TPA and ionomycin, suggest that TRH-stimulated Na+/H+ exchange plays no part in the acute stimulation of secretion, but that TRH increases the pH-sensitivity of the antiport system during increased synthesis of prolactin and growth hormone.

The mechanisms by which vasoactive intestinal peptide (VIP) and thyrotropin releasing hormone (TRH) stimulate prolactin release from pituitary cells

1990 ◽  
Vol 10 (2) ◽  
pp. 189-199 ◽  
Author(s):  
Trine Bjøro ◽  
Olav Sand ◽  
Bjørn Chr. Østberg ◽  
Jan O. Gordeladze ◽  
Peter Torjesen ◽  
...  
Keyword(s):  
Cell Membrane ◽  
Adenylate Cyclase ◽  
Vasoactive Intestinal Peptide ◽  
Lag Time ◽  
Thyrotropin Releasing Hormone ◽  
Pituitary Cells ◽  
Prolactin Release ◽  
Inositol Polyphosphates ◽  
Releasing Hormone ◽  
Electrophysiological Properties

The effect of vasoactive intestinal peptide (VIP) on prolactin (PRL) secretion from pituitary cells is reviewed and compared to the effect of thyrotropin releasing hormone (TRH). These two peptides induced different secretion profiles from parafused lactotrophs in culture. TRH was found to increase PRL secretion within 4 s and induced a biphasic secretion pattern, while VIP induced a monophasic secretion pattern after a lag time of 45–60 s. The secretion profiles are compared to changes in adenylate cyclase activity, production of inositol polyphosphates, changes in intracellular calcium concentrations and changes in electrophysiological properties of the cell membrane.

scholarly journals Mechanism of spontaneous intracellular calcium fluctuations in single GH4C1 rat pituitary cells

1993 ◽  
Vol 292 (1) ◽  
pp. 175-182 ◽  
Author(s):  
K A Wagner ◽  
P W Yacono ◽  
D E Golan ◽  
A H Tashjian
Keyword(s):  
Intracellular Calcium ◽  
Thyrotropin Releasing Hormone ◽  
Bay K 8644 ◽  
Pituitary Cells ◽  
Releasing Hormone ◽  
Quiescent Cells ◽  
Rat Pituitary ◽  
Rat Pituitary Cells ◽  
Ca2 Channels

Individual unstimulated GH4C1 cells exhibited spontaneous dynamic fluctuations in cytosolic free Ca2+ concentration ([Ca2+]i). Either chelation of extracellular Ca2+ with EGTA or treatment with nifedipine inhibited spontaneous [Ca2+]i fluctuations, indicating that the [Ca2+]i profile was dependent on the entry of extracellular Ca2+ via voltage-operated Ca2+ channels (VOCC). Spontaneous [Ca2+]i fluctuations did not resume immediately after exposure of EGTA-pretreated cells to extracellular Ca2+, supporting the hypothesis that the complex [Ca2+]i profiles observed in unstimulated cells required filling of an intracellular Ca2+ pool. BAY K 8644 elicited large rapid oscillations in [Ca2+]i. After chelation of extracellular Ca2+, however, re-addition of Ca2+ plus BAY K 8644 did not result in [Ca2+]i oscillations. The intracellular Ca2+ pool necessary for BAY K-induced oscillations was not the same Ins(1,4,5)P3-sensitive pool stimulated by thyrotropin-releasing hormone (TRH), because the TRH-stimulated Ins(1,4,5)P3-induced [Ca2+]i spike and the BAY K 8644-induced oscillations were differentially sensitive to chelation of extracellular Ca2+ and thapsigargin. Caffeine caused an increase in [Ca2+]i fluctuations in quiescent cells, supporting a role for Ca(2+)-induced Ca2+ release (CICR) in the generation of spontaneous [Ca2+]i fluctuations. In conclusion, the complex spontaneous changes in [Ca2+]i observed in single GH4C1 cells depend on both the influx of extracellular Ca2+ through VOCC and the action of an intracellular Ca2+ pool that increases [Ca2+]i through a CICR-like mechanism.

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