Cytosolic calcium elevation induced by orexin/hypocretin in granule cell domain cells of the rat cochlear nucleus in vitro.
Using rat brain slice preparations, we examined the effect of orexin on cytosolic Ca(2+) concentrations ([Ca(2+)](i)) in the granule cell domain (GCD) cells of the cochlear nucleus that carry non-auditory information to the dorsal cochlear nucleus. Application of orexin concentration-dependently increased [Ca(2+)](i), and in two thirds of GCD cells these increases persisted in the presence of tetrodotoxin. There was no significant difference between the dose-response curve for orexin-A and that for orexin-B. Extracellular Ca(2+) removal abolished the [Ca(2+)](i) elevation induced by orexin-B, whereas depletion of intracellular Ca(2+) stores had no effect. The orexin-B-induced elevation of [Ca(2+)](i) was not blocked by inhibitors of reverse-mode Na(+)/Ca(2+) exchanger (NCX) and nonselective cation channel, whereas it was blocked by lowering the extracellular Na(+) or by applying inhibitors of forward-mode NCX and voltage-gated R- and T-type Ca(2+) channels. The ORX-B-induced increase in [Ca(2+)](i) was also blocked by inhibitors of adenylcyclase (AC) and protein kinase A (PKA), but not by inhibitors of phosphatidylcholine-specific and phosphatidylinositol-specific phospholipase C. In electrophysiological experiments using whole-cell patch clamp recordings, half of GCD cells were depolarized by orexin-B, and the depolarization was abolished by a forward-mode NCX inhibitor. These results suggest that orexin increases [Ca(2+)](i) postsynaptically via orexin 2 receptors, and the increase in [Ca(2+)](i) is induced via the AC-PKA-forward-mode NCX-membrane depolarization-mediated activation of voltage-gated R- and T-type Ca(2+) channels. The results further support the hypothesis that the orexin system participates in integrating neural systems that are involved in arousal, sensory processing, energy homeostasis and autonomic function.
Nakamura
Yuki
Y
Division of Bio-Information Engineering, Faculty of Engineering, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan.
Miura
Shinya
S
Yoshida
Takashi
T
Kim
Juhyon
J
Sasaki
Kazuo
K
D000067956:Adenylyl Cyclase Inhibitors; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020908:Calcium Channels, R-Type / Q000378:metabolism; D020747:Calcium Channels, T-Type / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects; D017626:Cochlear Nucleus / Q000187:drug effects / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D047908:Intracellular Signaling Peptides and Proteins / Q000037:antagonists & inhibitors / Q000502:physiology*; D007473:Ion Channels / Q000037:antagonists & inhibitors; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009479:Neuropeptides / Q000037:antagonists & inhibitors / Q000502:physiology*; D000068797:Orexins; D009994:Osmolar Concentration; D020033:Protein Isoforms / Q000037:antagonists & inhibitors / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors; D013779:Tetrodotoxin / Q000494:pharmacology; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors
D000067956:Adenylyl Cyclase Inhibitors; D002121:Calcium Channel Blockers; D020908:Calcium Channels, R-Type; D020747:Calcium Channels, T-Type; D004791:Enzyme Inhibitors; D047908:Intracellular Signaling Peptides and Proteins; D007473:Ion Channels; D009479:Neuropeptides; D000068797:Orexins; D020033:Protein Isoforms; D019831:Sodium-Calcium Exchanger; C491711:nonselective cation channel protein, rat; D013779:Tetrodotoxin; D017868:Cyclic AMP-Dependent Protein Kinases; D010738:Type C Phospholipases