title: [Ca2+]i signaling between mitochondria and endoplasmic reticulum in neurons is regulated by microtubules. From mitochondrial permeability transition pore to Ca2+-induced Ca2+ release.
abstract: The positioning and dynamics of organelles depend on membrane-cytoskeleton interactions. Mitochondria relocate along microtubules (MT), but it is not clear whether MT have direct effects on mitochondrial function. Using two-photon microscopy and the mitochondrial fluorescent dyes rhodamine 123 and Rhod-2, we showed that Taxol and nocodazole, which correspondingly stabilize and disrupt MT, decreased potential and Ca(2+) in the mitochondria of brain stem pre-Botzinger complex neurons. Without changing basal cytoplasmic Ca(2+) ([Ca(2+)](i)), Taxol promoted the generation of [Ca(2+)](i) spikes in dendrites. These spikes were abolished after blockade of Ca(2+) influx and after depletion of internal Ca(2+) stores, indicating the involvement of Ca(2+)-induced Ca(2+) release. Nocodazole decreased mitochondrial potential and [Ca(2+)](m) and produced a long lasting increase in [Ca(2+)](i). MT-acting drugs depolarized single immobilized mitochondria and released previously stored Ca(2+). All of these effects were inhibited by pretreatment with blockers of mitochondrial permeability transition pore (mPTP), cyclosporin A, and 2-aminoethoxydiphenyl borate. Induction of mPTP by Taxol and nocodazole was confirmed by using a calcein/Co(2+) imaging technique. Electron and optical microscopy revealed tubulin bound to mitochondria. Mitochondria, MT, and endoplasmic reticulum (ER) showed strong co-localization, the degree of which decreased after MT were disrupted. We propose that changes in the structure of MT by Taxol and nocodazole promote the induction of mPTP. Subsequent Ca(2+) efflux stimulates the Ca(2+) release from the ER that drives spontaneous [Ca(2+)](i) transients. Thus, close positioning of mitochondria to the ER as determined by MT can be essential for the local [Ca](i) signaling in neurons.
authors.affiliation: Institute for Physiology, Georg August University, Humboldtallee 23, 37073 Göttingen, Germany. slm@ukps.gwdg.de
authors.forename: Sergej L
authors.initials: SL
authors.lastname: Mironov
authors.forename: Maxim V
authors.initials: MV
authors.lastname: Ivannikov
authors.forename: Mattias
authors.initials: M
authors.lastname: Johansson
mesh_terms: D000818:Animals; D020013:Calcium Signaling; D002478:Cells, Cultured; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D007473:Ion Channels / Q000378:metabolism; D051379:Mice; D008870:Microtubules / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D009474:Neurons / Q000378:metabolism; D015739:Nocodazole / Q000494:pharmacology; D017239:Paclitaxel / Q000494:pharmacology
chemical_list: D007473:Ion Channels; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D017239:Paclitaxel; D015739:Nocodazole