Bioluminescence imaging of mitochondrial Ca2+ dynamics in soma and neurites of individual adult mouse sympathetic neurons.
Changes in the cytosolic Ca(2+) concentration ([Ca(2+)](c)) are essential for triggering neurotransmitter release from presynaptic nerve terminals. Calcium-induced Ca(2+) release (CICR) from the endoplasmic reticulum (ER) may amplify the [Ca(2+)](c) signals and facilitate neurotransmitter release in sympathetic neurons. In adrenal chromaffin cells, functional triads are formed by voltage-operated Ca(2+) channels (VOCCs), CICR sites and mitochondria. In fact, mitochondria take up most of the Ca(2+) load entering the cells and are essential for shaping [Ca(2+)](c) signals and exocytosis. Here we have investigated the existence of such functional triads in sympathetic neurons. The mitochondrial Ca(2+) concentration ([Ca(2+)](m)) in soma and neurites of individual mouse superior cervical ganglion (SCG) neurons was monitored by bioluminescence imaging of targeted aequorins. In soma, Ca(2+) entry through VOCCs evoked rapid, near millimolar [Ca(2+)](m) increases in a subpopulation of mitochondria containing about 40% of the aequorin. Caffeine evoked a similar [Ca(2+)](m) increase in a mitochondrial pool containing about 30% of the aequorin and overlapping with the VOCC-sensitive pool. These observations suggest the existence of functional triads similar to the ones described in chromaffin cells. In neurites, mitochondria were able to buffer [Ca(2+)](c) increases resulting from activation of VOCCs but not those mediated by caffeine-induced Ca(2+) release from the ER. The weaker Ca(2+) buffering by mitochondria in neurites could contribute to facilitate Ca(2+)-induced exocytosis at the presynaptic sites.
Núñez
Lucía
L
Instituto de Biología y Genética Molecular, Universidad de Valladolid and Consejo Superior de Investigaciones Cientificas, 47003 Valladolid, Spain. nunezl@ibgm.uva.es
Senovilla
Laura
L
Sanz-Blasco
Sara
S
Chamero
Pablo
P
Alonso
María T
MT
Villalobos
Carlos
C
García-Sancho
Javier
J
D000331:Aequorin / Q000235:genetics; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D005822:Genetic Vectors; D018259:Herpesvirus 1, Human; D008163:Luminescent Measurements; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008928:Mitochondria / Q000378:metabolism*; D016501:Neurites / Q000378:metabolism; D009474:Neurons / Q000378:metabolism*; D017785:Photons; D013564:Sympathetic Nervous System / Q000378:metabolism*
D000331:Aequorin; D002118:Calcium