Sodium-level-sensitive sodium channel Na(x) is expressed in glial laminate processes in the sensory circumventricular organs.
Na(x) is an atypical sodium channel that is assumed to be a descendant of the voltage-gated sodium channel family. Our recent studies on the Na(x)-gene-targeting mouse revealed that Na(x) channel is localized to the circumventricular organs (CVOs), the central loci for the salt and water homeostasis in mammals, where the Na(x) channel serves as a sodium-level sensor of the body fluid. To understand the cellular mechanism by which the information sensed by Na(x) channels is transferred to the activity of the organs, we dissected the subcellular localization of Na(x) in the present study. Double-immunostaining and immunoelectron microscopic analyses revealed that Na(x) is exclusively localized to perineuronal lamellate processes extended from ependymal cells and astrocytes in the organs. In addition, glial cells isolated from the subfornical organ, one of the CVOs, were sensitive to an increase in the extracellular sodium level, as analyzed by an ion-imaging method. These results suggest that glial cells bearing the Na(x) channel are the first to sense a physiological increase in the level of sodium in the body fluid, and they regulate the neural activity of the CVOs by enveloping neurons. Close communication between inexcitable glial cells and excitable neural cells thus appears to be the basis of the central control of the salt homeostasis.
Watanabe
Eiji
E
Laboratory of Neurophysiology, National Institute for Basic Biology, 5-1 Higashiyama, Myodaiji-cho, Okazaki, Aichi 444-8787, Japan.
Hiyama
Takeshi Y
TY
Shimizu
Hidetada
H
Kodama
Ryuji
R
Hayashi
Noriko
N
Miyata
Seiji
S
Yanagawa
Yuchio
Y
Obata
Kunihiko
K
Noda
Masaharu
M
D000818:Animals; D002552:Cerebral Ventricles / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009457:Neuroglia / Q000378:metabolism*; D012679:Sense Organs / Q000378:metabolism*; D015222:Sodium Channels / Q000378:metabolism*; D014018:Tissue Distribution; D061566:Voltage-Gated Sodium Channels
C503483:Scn7a protein, mouse; D015222:Sodium Channels; D061566:Voltage-Gated Sodium Channels