scholarly journals Bay K 8644 reveals two components of L-type Ca2+ channel current in clonal rat pituitary cells.

1996 ◽  
Vol 108 (1) ◽  
pp. 1-11 ◽  
Author(s):  
D M Fass ◽  
E S Levitan
Keyword(s):  
Voltage Dependence ◽  
Slow Component ◽  
Fast Component ◽  
Bay K 8644 ◽  
Gh3 Cells ◽  
Pituitary Cells ◽  
Independent Manner ◽  
Channel Current ◽  
Rat Pituitary ◽  
Rat Pituitary Cells

Whole-cell L-type Ca2+ channel current was recorded in GH3 clonal rat pituitary cells using Ba2+ as a charge carrier. In the presence of the dihydropyridine agonist Bay K 8644, deactivation was best described by two exponential components with time constants of approximately 2 and approximately 8 ms when recorded at -40 mV. The slow component activated at more negative potentials than the fast component: Half-maximal activation for the slow and fast components occurred at approximately -15 and approximately 1 mV, respectively. The fast component was more sensitive to enhancement by racemic Bay K 8644 than the slow component: ED50fast = approximately 21 nM, ED50slow = approximately 74 nM. Thyrotropin-releasing hormone (TRH; 1 microM) inhibited the slow component by approximately 46%, whereas the fast component was inhibited by approximately 22%. TRH inhibition of total L-current showed some voltage dependence, but each Bay K 8644-revealed component of L-current was inhibited in a voltage-independent manner. Therefore, the apparent voltage dependence of TRH action is derived from complexities in channel gating rather than from relief of inhibition at high voltages. In summary, Bay K 8644-enhanced L-currents in GH3 cells consist of two components with different sensitivities to voltage, racemic Bay K 8644, and the neuropeptide TRH.

Characterization of a hyperpolarization-activated cation current in rat pituitary cells

1997 ◽  
Vol 272 (3) ◽  
pp. E405-E414 ◽  
Author(s):  
S. M. Simasko ◽  
S. Sankaranarayanan
Keyword(s):  
Primary Cultures ◽  
Gh3 Cells ◽  
Pituitary Cells ◽  
Sodium Permeability ◽  
Cation Current ◽  
Whole Cell Patch Clamp ◽  
Bath Application ◽  
Rat Pituitary ◽  
Rat Pituitary Cells

Whole cell patch-clamp techniques were used on clonal pituitary cells (GH3) and primary cultures of somatotrophs and lactotrophs to study currents that would be active at or below voltages for the threshold for action potential generation. When GH3 cells were held at -60 mV and pulsed to -120 mV, a slow-activating sustained inward current was observed (-16.5 +/- 1.5 pA in physiological baths, n = 72; approximately 1 s to half-maximal activation, voltage for 50% activation - 101 mV). The current was insensitive to bath application of 10 mM tetraethylammonium, 10 mM 4-aminopyridine, and 1 mM barium but was completely blocked by 3 mM cesium. The current was found to be a mixed cation current with a sodium permeability of 0.29 relative to potassium. These properties indicate that the current belongs to the hyperpolarization-activated cation current (Ih), or I(f), family of currents. However, the current was not altered by the addition of adenosine 3',5'-cyclic monophosphate (cAMP) to the pipette or forskolin to the bath. A similar but smaller current was observed in 15 of 16 somatotrophs but in only 1 of 9 lactotrophs. Application of cesium to spontaneously spiking GH3 cells or somatotrophs had no effect. However, cesium did block an inward holding current observed at -80 mV. These results demonstrate that the I(h) in pituitary cells does not serve as a pacemaking current but suggest that it may influence membrane potential responses when somatotrophs become hyperpolarized.

The effects of hypothalamic extracts and TRH on the growth and hormone production of GH3 cells in culture

1983 ◽  
Vol 104 (3) ◽  
pp. 287-294 ◽  
Author(s):  
Yukiko Yajima ◽  
Toshikazu Saito
Keyword(s):  
Dna Synthesis ◽  
Gel Filtration ◽  
Control Culture ◽  
Gh3 Cells ◽  
Thymidine Uptake ◽  
Pituitary Cells ◽  
Hormone Production ◽  
Hormone Synthesis ◽  
Rat Pituitary ◽  
Rat Pituitary Cells

Abstract. Hypothalamic factors were tested for their effects on the production of hormones and the growth of GH3 cells, cloned rat pituitary cells producing prolactin (Prl) and growth hormone (GH). Hypothalamic extracts (HE) (0.05 mg/ml) and TRH (0.3 μm) stimulated the synthesis of Prl to levels of 306% and 360%, respectively, of the control culture in a medium containing 0.5% foetal bovine serum (FBS) during a 24 h incubation. They did not affect the rate of GH production. The thymidine uptake was suppressed to 57% and 46% of the control by the addition of HE and TRH, respectively. They also inhibited the growth of GH3 to 70% and 74% of the control culture during an 8-day incubation period. On the other hand, LRH affected neither the rate of hormone production nor the thymidine uptake. Somatostatin suppressed the synthesis of Prl and GH, but it did not affect the incorporation of thymidine into the cells. The gel filtration studies of HE revealed that the inhibitory effects of HE on the thymidine uptake were dependent on two substances, TRH and an unknown factor(s) of high molecular nature. The relationship between hormone synthesis and DNA synthesis will be discussed on the basis of the TRH-induced effects on Prl production and DNA synthesis in GH3 cells.

Arachidonic acid mobilizes calcium and stimulates prolactin secretion from GH3 cells

1984 ◽  
Vol 246 (5) ◽  
pp. E458-E462 ◽  
Author(s):  
R. N. Kolesnick ◽  
I. Musacchio ◽  
C. Thaw ◽  
M. C. Gershengorn
Keyword(s):  
Arachidonic Acid ◽  
Saturated Fatty Acids ◽  
Arachidonic Acid Metabolism ◽  
Prolactin Secretion ◽  
Gh3 Cells ◽  
Pituitary Cells ◽  
Alpha Linolenic Acid ◽  
Rat Pituitary ◽  
Experimental Approaches ◽  
Rat Pituitary Cells

Because arachidonic acid and/or its metabolites may be intracellular effectors of calcium-mediated secretion, we studied whether arachidonic acid added exogenously mobilizes calcium and stimulates prolactin secretion from GH3 cells, cloned rat pituitary cells. Arachidonic acid caused efflux of 45Ca from preloaded cells and stimulated prolactin secretion. The concentration dependencies of these effects were similar; stimulation was attained with 3 microM arachidonic acid. To determine indirectly whether these effects may be caused by arachidonic acid itself, not via conversion to metabolites, two experimental approaches were used. First, inhibitors of arachidonic acid metabolism, eicosatetraynoic acid and indomethacin, did not inhibit arachidonic acid-induced prolactin secretion. And second, alpha-linolenic acid, which cannot be converted to arachidonic acid, and linoleic acid, but not saturated fatty acids of equal chain length, stimulated 45Ca efflux and prolactin secretion. These data demonstrate that arachidonic acid added exogenously causes Ca2+ mobilization and prolactin secretion from GH3 cells and suggest that arachidonic acid itself, not via metabolism, may be a cellular regulator of prolactin secretion.

Burmese Russell's viper venom causes hormone release from rat pituitary cells in vitro

1989 ◽  
Vol 122 (2) ◽  
pp. 489-494 ◽  
Author(s):  
G. R. Hart ◽  
C. Proby ◽  
G. Dedhia ◽  
T. H. Yeo ◽  
G. F. Joplin ◽  
...  
Keyword(s):  
Pituitary Hormone ◽  
Pituitary Cells ◽  
Hormone Release ◽  
Independent Manner ◽  
Column System ◽  
Rat Pituitary ◽  
Russell’S Viper ◽  
Rat Pituitary Cells

ABSTRACT Acute and chronic hypopituitarism is associated with severe envenoming by the Burmese Russell's viper. We have demonstrated that in vitro, Burmese Russell's viper venom (0·1–10 μg/ml) causes a dose-dependent release of GH, TSH and ACTH from dispersed rat anterior pituitary cells in culture. At 10 μg/ml, venom causes a significant increase in the release of GH (344%, P<0·001), TSH (168%, P<0·005) and ACTH (>700%, P<0·001). We have also shown that the component (or components) responsible for this stimulatory effect is stable to heat (60 °C, 1 h) and mild trypsinization. Repeated addition of venom (1 μg/ml) to pituitary cells in a perifusion column system demonstrated attenuation of GH release. This reduced response was not due to depletion of the GH pool since the pituitary cells were subsequently able to respond to both GH-releasing factor (GRF) stimulation and KCl depolarization. Somatostatin in a dose which abolished GRF-stimulated GH release failed to affect venom-stimulated GH release, implying that venom acts in a cyclic AMP-independent manner. We conclude that Burmese Russell's viper venom has direct effects on pituitary hormone release in vitro. Whether these effects contribute to its known actions in vivo on the function of the pituitary remains to be established. Journal of Endocrinology (1989) 122, 489–494

Somatostatin lowers the cytosolic free Ca2+ concentration in clonal rat pituitary cells (GH3 cells)

Cell Calcium ◽  
1984 ◽  
Vol 5 (3) ◽  
pp. 223-236 ◽  
Author(s):  
Werner Schlegel ◽  
François Wuarin ◽  
Claes B. Wollheim ◽  
Gaston R. Zahnd
Keyword(s):  
Gh3 Cells ◽  
Pituitary Cells ◽  
Rat Pituitary ◽  
Rat Pituitary Cells

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.

SPONTANEOUS RELEASE OF IMMUNOREACTIVE ACTH FROM ISOLATED RAT PITUITARY CELLS

1974 ◽  
Vol 77 (1_Suppl) ◽  
pp. S162
Author(s):  
H. L. Fehm ◽  
K. H. Voigt ◽  
R. Lang ◽  
M. Schleyer ◽  
E. F. Pfeiffer
Keyword(s):  
Pituitary Cells ◽  
Spontaneous Release ◽  
Rat Pituitary ◽  
Rat Pituitary Cells ◽  
Isolated Rat
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