Mitochondrial calcium sequestration and protein kinase C cooperate in the regulation of cortical F-actin disassembly and secretion in bovine chromaffin cells.
Mitochondria play an important role in the homeostasis of intracellular Ca(2+) and regulate its availability for exocytosis. Inhibitors of mitochondria Ca(2+) uptake such as protonophore CCCP potentiate the secretory response to a depolarizing pulse of K(+). Exposure of cells to agents that directly (cytochalasin D, latrunculin B) or indirectly (PMA) disrupt cortical F-actin networks also potentiate the secretory response to high K(+). The effects of cytochalasin D and CCCP on secretion were additive whereas those of PMA and CCCP were not; this suggests different mechanisms for cytochalasin D and CCCP and a similar mechanism for PMA and CCCP. Mitochondria were the site of action of CCCP, because the potentiation of secretion by CCCP was observed even after depletion of Ca(2+) from the endoplasmic reticulum. CCCP induced a small increase in the cytosolic Ca(2+) concentration ([Ca(2+)](c)) that was not modified by the protein kinase C (PKC) inhibitor chelerythrine. Both CCCP and PMA induced cortical F-actin disassembly, an effect abolished by chelerythrine. In addition, rotenone and oligomycin A, two other mitochondrial inhibitors, also evoked cortical F-actin disassembly and potentiated secretion; again, these effects were blocked by chelerythrine. CCCP also enhanced the phosphorylation of PKC and myristoylated alanine-rich C kinase substance (MARCKS), and these were also inhibited by chelerythrine. The results suggest that the rapid sequestration of Ca(2+) by mitochondria would protect the cell from an enhanced PKC activation and cortical F-actin disassembly, thereby limiting the magnitude of the secretory response.
Cuchillo-Ibáñez
I
I
Facultad de Medicina, Universidad Autónoma de Madrid, Madrid, Spain.
Lejen
T
T
Albillos
A
A
Rosé
S D
SD
Olivares
R
R
Villarroya
M
M
García
A G
AG
Trifaró
J-M
JM
D000199:Actins / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000031:analogs & derivatives* / Q000494:pharmacology; D002395:Catecholamines / Q000378:metabolism; D002417:Cattle; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000166:cytology / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008565:Membrane Proteins / Q000378:metabolism; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D019814:Myristic Acid / Q000378:metabolism; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D010766:Phosphorylation; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011522:Protons
D000199:Actins; D002395:Catecholamines; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D011522:Protons; D019814:Myristic Acid; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D011493:Protein Kinase C; D002118:Calcium