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

TY - JOUR

T1 - Thapsigargin, but not caffeine, blocks the ability of thyrotropin-releasing hormone to release Ca2+ from an intracellular store in GH4C1 pituitary cells

AU - Law, G J

AU - Pachter, J A

AU - Thastrup, Ole

AU - Hanley, M R

AU - Dannies, P S

PY - 1990

Y1 - 1990

N2 - 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.

AB - 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.

KW - 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester

KW - Animals

KW - Caffeine

KW - Calcium

KW - Cell Line

KW - Inositol Phosphates

KW - Kinetics

KW - Nimodipine

KW - Pituitary Neoplasms

KW - Plants, Medicinal

KW - Prolactin

KW - Terpenes

KW - Thapsigargin

KW - Thyrotropin-Releasing Hormone

KW - Tumor Cells, Cultured

M3 - Journal article

C2 - 1692207

SN - 0264-6021

VL - 267

SP - 359

EP - 364

JO - Biochemical Journal

JF - Biochemical Journal

IS - 2

ER -