Stimulation-Evoked Increases in Cytosolic [Ca²⁺] in Mouse Motor Nerve Terminals Are Limited by Mitochondrial Uptake and Are Temperature-Dependent

Abstract

Increases in cytosolic [Ca 2ϩ ] evoked by trains of action potentials (20-100 Hz) were recorded from mouse and lizard motor nerve terminals filled with a low-affinity fluorescent indicator, Oregon Green BAPTA 5N. In mouse terminals at nearphysiological temperatures (30-38°C), trains of action potentials at 25-100 Hz elicited increases in cytosolic [Ca 2ϩ ] that stabilized at plateau levels that increased with stimulation frequency. Depolarization of mitochondria with carbonylcyanide m-chlorophenylhydrazone (CCCP) or antimycin A1 caused cytosolic [Ca 2ϩ ] to rise to much higher levels during stimulation. ] measured with fluorescent indicators increases rapidly at first but then stabilizes at a plateau level until stimulation ceases (Steunkel, 1994;Ravin et al., 1997;David et al., 1998). This stabilization of average cytosolic [Ca 2ϩ ] during continued Ca 2ϩ influx is disrupted by agents that inhibit mitochondrial Ca 2ϩ uptake (Steunkel, 1994;David et al., 1998), suggesting that mitochondrial Ca 2ϩ uptake contributes importantly to sequestration of the Ca 2ϩ loads entering stimulated nerve terminals. Ca 2ϩ uptake via the mitochondrial uniporter is driven by the large negative potential (approximately Ϫ150 to Ϫ200 mV) created by proton transport across the inner mitochondrial membrane (for review, see Gunter and Pfeiffer, 1990).For some secretory cells, additional evidence for mitochondrial Ca 2ϩ uptake has been obtained using fluorescent or luminescent indicators localized within the mitochondrial matrix. Increases in matrix [Ca 2ϩ ] evoked by depolarization and/or hormones have been demonstrated in adrenal chromaffin cells (Babcock et al., 1997;Montero et al., 2000) and lizard motor nerve terminals (David et al., 1998). Mitochondrial Ca uptake has also been demonstrated by electron probe microanalysis of total Ca in frog sympathetic ganglion neurons fast-frozen after a 45 sec bath application of 50 mM K ϩ (Pivovarova et al., 1999). Simultaneous imaging of cytosolic and mitochondrial [Ca 2ϩ ] showed that, in lizard motor nerve terminals, mitochondrial Ca 2ϩ uptake begins after as few as 25-50 action potentials delivered at 50 -100 Hz, at approximately the same time that cytosolic [Ca 2ϩ ] reaches a plateau (David et al., 1998). In this preparation, as in crayfish motor nerve terminals, adrenal chromaffin cells, and several types of neuronal somata, mitochondria have been shown to be the dominant means of sequestering moderate to large Ca 2ϩ loads (Friel and Tsien, 1994;Werth and Thayer, 1994;White and Reynolds, 1995;Herrington et al., 1996;Park et al., 1996;Tang and Zucker, 1997;David, 1999;Colegrove et al., 2000).The present study was undertaken to measure cytosolic [Ca 2ϩ ] transients evoked by physiological stimulation in mammalian (mouse) motor nerve terminals and to determine whether mitochondrial Ca 2ϩ sequestration contributes to limiting the magnitude of these transients. We demonstrate that, at temperatures near physiological (33-38°C), the elevation of average cytosolic [Ca 2ϩ ] stab...

Roles of mitochondria and temperature in the control of intracellular calcium in adult rat sensory neurons

“…Only inhibition of mitochondrial Ca 2+ uptake by 2 μM ruthenium red significantly reversed the reduced [Ca 2+ ] i , τ r , and increased Buffer Index observed at 30 °C providing substantial evidence that mitochondrial Ca 2+ uptake is necessary for the observed temperature-dependencies of [Ca 2+ ] i , τ r , and the Buffer Index in Na + -poor conditions. This observation is consistent with previous work by ourselves [15] and others [16][17][18] pointing to a temperature-sensitivity in mitochondrial control of [Ca 2+ ] i .…”

“…Thus, there is relatively little information on the control of [Ca 2+ ] i in DRG neurons of adult rats, the primary experimental model for studies of somatic sensation including nociception, at warmer temperatures. That temperature might be an important parameter is suggested by reports that warming increases Ca 2+ buffering by mitochondria [15][16][17][18]. A temperature-dependent increase in Ca 2+ buffering by the mitochondria is expected to limit the ability of Ca 2+ influx to raise global [Ca 2+ ] i .…”

Strong Effects of Subphysiological Temperature on the Function and Plasticity of Mammalian Presynaptic Terminals

“…Consistent with our results, a weak tetanus led to a much stronger NMDA-dependent potentiation of Schaffer collaterals in hippocampal slices when applied at 23°C compared with 32°C (McNaughton et al, 1994). This temperature-dependent variability in synaptic plasticity may be attributable to a number of concurrent changes occurring at room temperature, including broadening of action potentials (Thompson et al, 1985;Shen and Schwartzkroin, 1988;Volgushev et al, 2000a,b), larger Ca 2ϩ influx produced by an action potential (Borst and Sakmann, 1998;David and Barrett, 2000;Dinkelacker et al, 2000), and easier removal of the Mg 2ϩ block of NMDA receptor attributable to membrane depolarization (Volgushev et al, 2000a,b). All of these factors are expected to lower the threshold for induction of plastic changes.…”

Synaptic Vesicles: Test for a Role in Presynaptic Calcium Regulation

“…could not be detected Just as the amplitude of the Ca 2ϩ response to stimulation in lizard MN terminals increases when sequestration of Ca 2ϩ by mitochondria is blocked (David and Barrett, 2000) we predicted an increase in the Ca 2ϩ response in Drosophila MN terminals depleted of SVs. However, in response to 80 Hz stimulation, MN terminals depleted of SVs showed no change in the rate of rise in [Ca 2ϩ ] i , the amplitude of the plateau achieved after 1 sec, or the subsequent decay in [Ca 2ϩ ] i relative to nondepleted MN terminal boutons (Fig.…”