Control of secretion by mitochondria depends on the size of the local [Ca2+] after chromaffin cell stimulation.
In chromaffin cells, plasma membrane calcium (Ca2+) channels and mitochondria constitute defined functional units controlling the availability of Ca2+ nearby exocytotic sites. We show here that, when L-/N-type Ca2+ channels were inhibited with nisoldipine and omega-conotoxin GVIA, cytosolic [Ca2+] ([Ca2+]c) peaks measured in fura-4F-loaded cells were reduced by 36%; however, mitochondrial Ca2+ uptake was unaffected and secretion was potentiated by protonophores as in control cells. By contrast, when non L-type Ca2+ channels were inhibited with omega-conotoxin MVIIC, [Ca2+]c peaks induced by high K+ were reduced by 73%, mitochondrial Ca2+ uptake was abolished, and secretion was not modified by protonophores. However, if Ca2+ entered only through L-type channels activated by FPL64176, high K+ stimulation induced fast mitochondrial Ca2+ uptake and catecholamine secretion was strongly increased and potentiated by protonophores. These results confirm the close association of catecholamine secretion to mitochondrial Ca2+ uptake, and indicate the sharp threshold of local [Ca2+]c (about 5 microM) required for triggering fast mitochondrial Ca2+ uptake that is able to modulate secretion. The entry of Ca2+ through L-type channels generated local [Ca2+]c increases just below that, inducing little mitochondrial Ca2+ uptake unless FPL64176 was present. By contrast, Ca2+ entry through P/Q-type channels fully activated mitochondrial Ca2+ uptake. Control of secretion by mitochondria therefore depends critically on the ability of the stimulus to create large local [Ca2+]c microdomains.
Montero
M
M
Instituto de Biología y Genética Molecular, Universidad de Valladolid y Consejo Superior de Investigaciones Científicas, Departamento de Bioquímica y Biología Molecular y Fisiología, Facultad de Medicina, Ramón y Cajal 7, E-47005 Valladolid, Spain.
Alonso
M T
MT
Albillos
A
A
Cuchillo-Ibáñez
I
I
Olivares
R
R
G  García
A
A
García-Sancho
J
J
Alvarez
J
J
D000313:Adrenal Medulla / Q000187:drug effects / Q000378:metabolism*; D000331:Aequorin / Q000494:pharmacology; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002120:Calcium Channel Agonists / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002417:Cattle; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured / Q000187:drug effects / Q000378:metabolism; D019439:Chromaffin Cells / Q000187:drug effects / Q000378:metabolism*; D016257:Fura-2 / Q000031:analogs & derivatives / Q000493:pharmacokinetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D015737:Nisoldipine / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology; D011758:Pyrroles / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects / Q000378:metabolism; D020866:omega-Conotoxin GVIA / Q000494:pharmacology; D020960:omega-Conotoxins / Q000494:pharmacology
D002120:Calcium Channel Agonists; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D011758:Pyrroles; D019837:Ryanodine Receptor Calcium Release Channel; D020960:omega-Conotoxins; C071658:FPL 64176; C075851:omega-conotoxin-MVIIC; C087512:fura F; D002110:Caffeine; D015737:Nisoldipine; D000331:Aequorin; D020866:omega-Conotoxin GVIA; D011188:Potassium; D002118:Calcium; D016257:Fura-2