Baseline cytosolic Ca2+ oscillations derived from a non-endoplasmic reticulum Ca2+ store.
Cytosolic Ca(2+) oscillations can be due to cycles of release and re-uptake of internally stored Ca(2+). To investigate the nature of these Ca(2+) stores, we expressed the Pmr1 Ca(2+) pump of Caenorhabditis elegans in COS-1 cells and pretreated the cells with thapsigargin to prevent Ca(2+) uptake by the sarco(endo)plasmic reticulum Ca(2+)-ATPase. Pmr1 co-localized with the Golgi-specific 58K protein and was targeted to a Ca(2+) store that was less leaky for Ca(2+) than the endoplasmic reticulum and whose inositol trisphosphate receptors were less sensitive to inositol trisphosphate and ATP than those in the endoplasmic reticulum. ATP-stimulated Pmr1-overexpressing cells responded after a latency to extracellular Ca(2+) with a regenerative Ca(2+) signal, which could be prevented by caffeine. They also produced very stable ilimaquinone-sensitive baseline Ca(2+) spikes, even in the presence of thapsigargin. Such responses never occurred in non-transfected cells or in cells that overexpressed the type-1 sarco(endo)plasmic reticulum Ca(2+)-ATPase. Abortive Ca(2+) spikes also occurred in histamine-stimulated untransfected HeLa cells pretreated with thapsigargin, and they too were inhibited by ilimaquinone. We conclude that the Pmr1-induced Ca(2+) store, which probably corresponds to the Golgi compartment, can play a crucial role in setting up baseline Ca(2+) spiking.
Missiaen
L
L
Laboratorium voor Fysiologie, K.U. Leuven Campus Gasthuisberg O/N, Herestraat 49, Leuven B-3000, Belgium. Ludwig.Missiaen@med.kuleuven.ac.be
Van Acker
K
K
Parys
J B
JB
De Smedt
H
H
Van Baelen
K
K
Weidema
A F
AF
Vanoevelen
J
J
Raeymaekers
L
L
Renders
J
J
Callewaert
G
G
Rizzuto
R
R
Wuytack
F
F
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D019556:COS Cells; D017173:Caenorhabditis elegans / Q000378:metabolism; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D002460:Cell Line; D000697:Central Nervous System Stimulants / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D015151:Immunoblotting; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008856:Microscopy, Fluorescence; D011485:Protein Binding; D011817:Rabbits; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection
D015220:Calcium Channels; D000697:Central Nervous System Stimulants; C506926:ITPR1 protein, human; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D002110:Caffeine; D000255:Adenosine Triphosphate; D002118:Calcium