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- Title
Na<sup>+</sup>/Ca<sup>2+</sup> Exchange and Ca<sup>2+</sup> Homeostasis in Axon Terminals of Mammalian Central Neurons.
- Authors
LEE, SUK‐HO; KIM, MYOUNG‐HWAN; LEE, JU‐YOUNG; LEE, SANG HUN; LEE, DOYUN; PARK, KYEONG HAN; HO, WON‐KYUNG
- Abstract
We investigated Ca2+ clearance mechanisms (CCMs) at the axon terminals of mammalian central neurons: neurohypophysial (NHP) axon terminals and calyces of Held. Ca2+ transients were evoked by applying a short depolarization pulse via a patch pipette containing Ca2+ indicator dye. Quantitative analysis of the Ca2+ decay phases revealed that Na+/Ca2+ exchange (Na/CaX) is a major CCM at both axon terminals. In contrast, no Na/CaX activity was found in the somata of NHP axon terminals (supraoptic magnocellular neurons), indicating that the distribution of Na+/Ca2+ exchangers is polarized. Intracellular dialysis of axon terminals with a K+-free pipette solution attenuated the Na/CaX activities by 90% in the NHP axon terminals and by 60% at the calyx of Held, indicating that K+-dependent Na+/Ca2+ exchangers are involved. Studying the effects of specific inhibitors of smooth endoplasmic reticulum Ca2+-ATPase (SERCA) and plasma membrane Ca2+-ATPase (PMCA) on the Ca2+ decay rate revealed that PMCA contributed 23% of total Ca2+ clearance, but that SERCA made no contribution at the calyx of Held. The contribution of mitochondria was negligible for small Ca2+ transients, but became apparent at peak Ca2+ levels higher than 2.5 μM. When mitochondrial function was inhibited, the dependence of CCMs on [Ca2+] i at the calyx of Held showed saturation kinetics with K1/2= 1.7 μM, suggesting that the Na/CaX activity is saturated at high [Ca2+] i. The presynaptic Na+/Ca2+ exchanger activity, which competes for cytosolic Ca2+ with mitochondria, may contribute to nonplastic synaptic transmission at these axon terminals.
- Subjects
CALCIUM in the body; SODIUM; CELL physiology; HOMEOSTASIS; NEURAL physiology; MAMMALS; SUPRAOPTIC nucleus; MITOCHONDRIA
- Publication
Annals of the New York Academy of Sciences, 2007, Vol 1099, p396
- ISSN
0077-8923
- Publication type
Article
- DOI
10.1196/annals.1387.011