Sodium-gated cation channel implicated in the activation of lobster
olfactory receptor neurons.
Aslbek B. Zhainazarov, Richard E. Doolin, and Barry W. Ache..
Whitney Laboratory and Depts. of Zoology and Neuroscience, Univ. of
Florida, St. Augustine, FL 32086-8623..
APStracts 4:315N, 1997.
ABSTRACT
The role of Na+-activated channels in cellular function, if any, is still
elusive. Here, we implicate a Na+-activated nonselective cation channel in the
activation of lobster olfactory receptor neurons. We show that a Na+-activated
channel occurs in the transduction compartment (outer dendrite) of the
receptor cells. The channel density in the outer dendrite (17.3 æm-2) is two
orders of magnitude greater than that in the soma of the cells (0.06 æm-2).
The properties of the channel in the outer dendrite are identical to those
described earlier in detail for a Na+-activated channel on the soma of the
cells in culture. The channel is specifically activated by intracellular Na+
in a concentration-dependent manner [EC50= 49.2ñ3.0 (S.E.M.) mM] in cell-free
patches in the absence of both divalent cations and nucleoside triphosphates.
The presence of a Na+-activated channel in a cellular compartment specialized
for odor transduction suggests that the channel functions in odor activation.
Two separate lines of experimental evidence support this view. (1) Two
pharmacological probes (W7 and trifluoperazine) which block the Na+-gated
channel from outside in excised patches [IC50: 16.3ñ1.5 (S.E.M.) æM for W7;
14.4ñ0.9 æM for trifluoperazine], significantly reduce odor-evoked responses
when applied focally to the outer dendrite of the cells. (2) The response of
the cells to odors is specific for Na+. Substituting Na+ with either Li+ or
NH4+, both of which permeate the cell but do not activate the Na+-gated
channel, also significantly reduces the odor-evoked response of the cells,
implying that a substantial part of the odor-evoked depolarization can be
ascribed to a Na+-activated conductance. We hypothesize, therefore, that the
Na+-activated channel amplifies the receptor current as a result of being
secondarily activated by the primary odor transduction pathway.
Received 18 September 1997; accepted in final form 4 November 1997.
APS Manuscript Number J769-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 14 November 1997