Evidence that mitochondria buffer physiological Ca²⁺ loads in lizard motor nerve terminals

Abstract

Changes in cytosolic and mitochondrial [Ca2+] produced by brief trains of action potentials were measured in motor nerve terminals using a rapidly scanning confocal microscope. Cytosolic [Ca2+] was measured using ionophoretically injected Oregon Green BAPTA 5N (OG‐5N). Mitochondrial [Ca2+] was measured using rhod‐2, bath loaded as dihydrorhod‐2. In response to 100‐250 stimuli at 25‐100 Hz the average cytosolic [Ca2+] showed an initial rapid increase followed by a much slower rate of increase. Mitochondrial [Ca2+] showed no detectable increase during the first fifteen to twenty stimuli, but after this initial delay also showed an initially rapid rise followed by a slower rate of increase. The onset of the increase in mitochondrial [Ca2+] coincided with the slowing of the rate of rise of cytosolic [Ca2+]. The peak levels of cytosolic and mitochondrial [Ca2+] both increased with increasing frequencies of stimulation. When stimulation terminated, the initial rate of decay of cytosolic [Ca2+] was much more rapid than that of mitochondrial [Ca2+]. After addition of carbonyl cyanide m‐chlorophenyl hydrazone (CCCP, 1‐2 μm) to dissipate the proton electrochemical gradient across the mitochondrial membrane, cytosolic [Ca2+] rose rapidly throughout the stimulus train, reaching levels much higher than normal. CCCP inhibited the increase in mitochondrial [Ca2+]. These results suggest that mitochondrial uptake of Ca2+ contributes importantly to buffering presynaptic cytosolic [Ca2+] during normal neuromuscular transmission.

Release of Ca2+ from the sarcoplasmic reticulum increases mitochondrial [Ca2+] in rat pulmonary artery smooth muscle cells

“…1997; David et al 1998) and mitochondrially targeted aequorin (Rizzuto et al 1998;Nakazaki et al 1998) Fig. 2C).…”

Mechanisms of Prolonged Presynaptic Ca2+Signaling and Glutamate Release Induced by TRPV1 Activation in Rat Sensory Neurons

“…It is generally agreed that Ca 2ϩ uptake by presynaptic mitochondria is mediated by the mitochondrial Ca 2ϩ uniporter (Tang and Zucker, 1997;David et al, 1998;Billups and Forsythe, 2002). Which mechanisms are responsible for Ca 2ϩ efflux from mitochon- dria is less clear.…”

Target Cell-Specific Involvement of Presynaptic Mitochondria in Post-Tetanic Potentiation at Hippocampal Mossy Fiber Synapses

“…2؉ buffering during HFS at large and small MFBs Mitochondria have been suggested as a Ca 2ϩ sequestration mechanism at the axon terminals of many synapses (Tang and Zucker, 1997;David et al, 1998;David and Barrett, 2000;Billups and Forsythe, 2002;Suzuki et al, 2002;Kim et al, 2005;GarciaChacon et al, 2006 (Fig. 3Aa,Ab, black traces).…”