[Ca2+] microdomains control agonist-induced Ca2+ release in intact HeLa cells.
We have monitored specifically the [Ca2+] in the lumen of the endoplasmic reticulum (ER) of intact HeLa cells using an ER-targeted low-Ca2+-affinity aequorin. The steady-state [Ca2+] in the ER was around 600 microM. Histamine induced a concentration-dependent decrease in lumenal [Ca2+], whose rate increased near one order of magnitude and became "quantal" when cytosolic [Ca2+] ([Ca2+]c) was clamped with the Ca2+ chelator BAPTA. This effect was not due to decreased Ca2+ pumping because simultaneous addition of a SERCA inhibitor produced only additive effects. Given that inhibition by [Ca2+]c of the inositol 1,4,5-trisphosphate-gated channels requires a [Ca2+]c much higher than that observed in the bulk cytosol after histamine addition, we conclude that local [Ca2+]c microdomains at the site of release strongly inhibit agonist-induced Ca2+ mobilization in intact cells. This effect should play a key role in the mechanism controlling cytosolic [Ca2+] oscillations and waves, and therefore in the generation of spatio-temporal Ca2+ patterns.
Montero
M
M
Departamento de Bioquímica y Fisiología, IBGM, Facultad de Medicina, Universidad de Valladolid and CSIC, Spain.
Barrero
M J
MJ
Alvarez
J
J
D002118:Calcium / Q000378:metabolism*; D002138:Calibration; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006367:HeLa Cells; D006632:Histamine / Q000494:pharmacology; D006801:Humans; D006873:Hydroquinones / Q000494:pharmacology
D006873:Hydroquinones; C019359:2,5-di-tert-butylhydroquinone; D006632:Histamine; D002118:Calcium