Mitochondrial Ca(2+)-induced Ca(2+) release mediated by the Ca(2+) uniporter.
We have reported that a population of chromaffin cell mitochondria takes up large amounts of Ca(2+) during cell stimulation. The present study focuses on the pathways for mitochondrial Ca(2+) efflux. Treatment with protonophores before cell stimulation abolished mitochondrial Ca(2+) uptake and increased the cytosolic [Ca(2+)] ([Ca(2+)](c)) peak induced by the stimulus. Instead, when protonophores were added after cell stimulation, they did not modify [Ca(2+)](c) kinetics and inhibited Ca(2+) release from Ca(2+)-loaded mitochondria. This effect was due to inhibition of mitochondrial Na(+)/Ca(2+) exchange, because blocking this system with CGP37157 produced no further effect. Increasing extramitochondrial [Ca(2+)](c) triggered fast Ca(2+) release from these depolarized Ca(2+)-loaded mitochondria, both in intact or permeabilized cells. These effects of protonophores were mimicked by valinomycin, but not by nigericin. The observed mitochondrial Ca(2+)-induced Ca(2+) release response was insensitive to cyclosporin A and CGP37157 but fully blocked by ruthenium red, suggesting that it may be mediated by reversal of the Ca(2+) uniporter. This novel kind of mitochondrial Ca(2+)-induced Ca(2+) release might contribute to Ca(2+) clearance from mitochondria that become depolarized during Ca(2+) overload.
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, E-47005 Valladolid, Spain.
Alonso
M T
MT
Albillos
A
A
García-Sancho
J
J
Alvarez
J
J
D000331:Aequorin / Q000235:genetics; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology*; D015220:Calcium Channels; D002135:Calcium-Binding Proteins / Q000378:metabolism* / Q000494:pharmacology; D002417:Cattle; D019439:Chromaffin Cells / Q000166:cytology; D002998:Clonazepam / Q000031:analogs & derivatives / Q000494:pharmacology; D016572:Cyclosporine / Q000494:pharmacology; D008164:Luminescent Proteins; D008928:Mitochondria / Q000737:chemistry* / Q000187:drug effects; D011188:Potassium / Q000494:pharmacology; D012430:Ruthenium Red / Q000494:pharmacology; D013841:Thiazepines / Q000494:pharmacology
D015220:Calcium Channels; D002135:Calcium-Binding Proteins; D008164:Luminescent Proteins; D013841:Thiazepines; C034703:mitochondrial calcium uniporter; D012430:Ruthenium Red; D000331:Aequorin; D002998:Clonazepam; C079032:CGP 37157; D016572:Cyclosporine; D011188:Potassium; D002118:Calcium