Redistribution of Ca2+ among cytosol and organella during stimulation of bovine chromaffin cells.
Recent results indicate that Ca2+ transport by organella contributes to shaping Ca2+ signals and exocytosis in adrenal chromaffin cells. Therefore, accurate measurements of [Ca2+] inside cytoplasmic organella are essential for a comprehensive analysis of the Ca2+ redistribution that follows cell stimulation. Here we have studied changes in Ca2+ inside the endoplasmic reticulum, mitochondria, and nucleus by imaging aequorins targeted to these compartments in cells stimulated by brief depolarizing pulses with high K+ solutions. We find that Ca2+ entry through voltage-gated Ca2+ channels generates subplasmalemmal high [Ca2+]c domains adequate for triggering exocytosis. A smaller increase of [Ca2+]c is produced in the cell core, which is adequate for recruitment of the reserve pool of secretory vesicles to the plasma membrane. Most of the Ca2+ load is taken up by a mitochondrial pool, M1, closer to the plasma membrane; the increase of [Ca2+]M stimulates respiration in these mitochondria, providing local support for the exocytotic process. Relaxation of the [Ca2+]c transient is due to Ca2+ extrusion through the plasma membrane. At this stage, mitochondria release Ca2+ to the cytosol through the Na+/Ca2+ exchanger, thus maintaining [Ca2+]c discretely increased, especially at core regions of the cell, for periods that outlast the duration of the stimulus.
Villalobos
Carlos
C
Instituto de Biología y Genética Molecular, Universidad de Valladolid y Consejo Superior de Investigaciones Científicas, Departamento de Fisiología y Bioquímica, Facultad de Medicina, E-47005 Valladolid, Spain..
Nuñez
Lucía
L
Montero
Mayte
M
García
Antonio G
AG
Alonso
Maria Teresa
MT
Chamero
Pablo
P
Alvarez
Javier
J
García-Sancho
Javier
J
D000331:Aequorin / Q000032:analysis; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000187:drug effects / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D017136:Ion Transport; D007700:Kinetics; D008856:Microscopy, Fluorescence; D008928:Mitochondria / Q000378:metabolism; D009243:NAD / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology
D009243:NAD; D000331:Aequorin; D011188:Potassium; D002118:Calcium