Evidence for multiple intracellular calcium pools in GH4C1 cells: investigations using thapsigargin.
The actions of thapsigargin (Tg), a plant sesquiterpene lactone, on Ca2+ homeostasis were investigated in digitonin-permeabilized GH4C1 rat pituitary cells. Tg (1 microM) caused a rapid and sustained increase in ambient Ca2+ concentration [( Ca2+]) and inhibited the rise in [Ca2+] induced by subsequent addition of TRH (100 nM), inositol 1,4,5-trisphosphate (IP3, 10 microM), or the nonhydrolyzable GTP analogue guanosine 5'-0-(3-thiotriphosphate) (GTP gamma S, 10 microM). However, neither IP3 nor GTP gamma S pretreatment, which themselves release sequestered Ca2+, prevented the Ca2+ accumulation induced by Tg. Pretreatment with heparin (100 micrograms/ml, 10 min), an IP3 receptor antagonist, did not affect Ca2+ accumulation induced by Tg, although it abolished the rise in [Ca2+] induced by IP3. The ability of Tg to increase [Ca2+] was dependent on added ATP. We conclude that, in GH4C1 cells, Tg acts, in part, on TRH-, IP3- and GTP gamma S-sensitive Ca2+ pools; however, Tg also acts on an ATP-dependent pool of intracellular Ca2+ which is not sensitive to TRH, IP3 or GTP gamma S, indicating a complexity of intracellular Ca2+ pools not previously appreciated in these cells.
Koshiyama
H
H
Laboratory of Toxicology, Harvard School of Public Health, Boston, MA.
Tashjian
A H
AH
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels; D002460:Cell Line; D002463:Cell Membrane Permeability; D004072:Digitonin / Q000494:pharmacology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006493:Heparin / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007700:Kinetics; D010911:Pituitary Neoplasms; D051381:Rats; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000502:physiology; D018160:Receptors, Cytoplasmic and Nuclear; D013729:Terpenes / Q000494:pharmacology*; D019284:Thapsigargin; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology
D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; D013729:Terpenes; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D013973:Thyrotropin-Releasing Hormone; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate; D006493:Heparin; D004072:Digitonin; D002118:Calcium