Inositol trisphosphate producing agonists do not mobilize the thapsigargin-insensitive part of the endoplasmic-reticulum and Golgi Ca2+ store.
Non-mitochondrial intracellular Ca2+ stores contain both thapsigargin-sensitive sarco(endo)plasmic-reticulum Ca2+-ATPases (SERCA) and thapsigargin-insensitive secretory-pathway Ca2+-ATPases (SPCA1). We now have studied the Ca2+-release properties of the compartments associated with these pumps in intact, i.e. non-permeabilized, cells of different origin (HeLa, keratinocytes, 16HBE14o-, COS-1, A7r5) and with different approaches (45Ca2+ fluxes, Ca2+ imaging and measurements of the free luminal [Ca2+] in the endoplasmic-reticulum and the Golgi apparatus using targeted aequorin). Application of an extracellular agonist in the absence of thapsigargin induced in all cells a Ca2+ release from both the endoplasmic-reticulum and the Golgi apparatus. The agonists were not able to release Ca2+ in the presence of 10 microM thapsigargin, except in COS-1 cells overexpressing SPCA1, where this pump not only appeared in the Golgi compartment but also overflowed into the agonist-sensitive part of the endoplasmic-reticulum. We conclude that the subcompartments of the endoplasmic-reticulum and of the Golgi complex that endogenously express SPCA1 are insensitive to agonist stimulation.
Vanoevelen
J
J
Laboratorium voor Fysiologie, K.U. Leuven Campus Gasthuisberg O/N, Leuven, Belgium
Raeymaekers
L
L
Parys
J B
JB
De Smedt
H
H
Van Baelen
K
K
Callewaert
G
G
Wuytack
F
F
Missiaen
L
L
D000818:Animals; D019556:COS Cells; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D006056:Golgi Apparatus / Q000187:drug effects / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000819:agonists* / Q000096:biosynthesis*; D008297:Male; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D019284:Thapsigargin / Q000494:pharmacology*
D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; C403624:ATP2C1 protein, human; D000252:Calcium-Transporting ATPases; D002118:Calcium