The Journal of Neuroscience, December 1, 2001, 21(23):9168-9174
P2X2 Receptor Mediates Stimulation of Parasensory
Cation Absorption by Cochlear Outer Sulcus Cells and Vestibular
Transitional Cells
Jun Ho
Lee,
Toshihiko
Chiba, and
Daniel C.
Marcus
Department of Anatomy and Physiology, Kansas State University,
Manhattan, Kansas 66506
Cochlear outer sulcus cells (OSC) and vestibular transitional cells
(VTC) are part of the parasensory epithelium in the inner ear and are
located in homologous positions between the sensory hair cells and the
cation secretory epithelial cells in the cochlea and the vestibular
labyrinth. OSC are known to sustain a reabsorptive transepithelial
current and to contain an immunoreactivity for P2X2
purinergic receptors. This study addresses whether OSC and VTC share
functional similarities and extends this hypothesis to the question of
whether both cell types contain functional P2X2 receptors.
The current density (Isc) was
recorded with the vibrating probe technique and was found to be similar
in VTC and OSC. Both gadolinium and flufenamic acid reduced
Isc in VTC, as reported previously for OSC.
Isc was stimulated by extracellular ATP but
not by selective agonists of P2Y receptors. Purinergic receptor
agonists increased Isc with a potency
order of ATP > 2'- and
3'-O-(4-benzoyl-benzoyl)adenosine
5'-triphosphate 
,
-methyleneadenosine 5'-triphosphate in both OSC and VTC. In the presence of suramin (100 µM) or gadolinium (100 µM), the
responses of ATP were inhibited significantly in both OSC and VTC. This
pharmacological profile is consistent with that of the P2X2
receptor. These results demonstrate that VTC participate in vestibular
parasensory cation absorption and that both OSC and VTC regulate their
parasensory cation flux via P2X2 receptors, which would
regulate the endolymphatic concentration of the current-carrying ion
species in auditory and vestibular transduction.
Key words:
voltage-sensitive vibrating probe; regulation of
transduction; P2X receptor; inner ear; cochlea; vestibular end
organ
Copyright © 2001 Society for Neuroscience 0270-6474/01/21239168-07$05.00/0
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