Author:
STUART ANN E.,GEBHARDT KELLEY A.,VOGEL STACY N.,RODRIGUEZ OLGA
Abstract
Using autoradiographic and biochemical techniques, we studied
the sodium-dependent forward and reverse transport of the
neurotransmitter histamine in an arthropod photoreceptor in
order to test whether the transporter plays a central role in
visual signal transfer at this synapse. In particular, we asked
whether the histamine transporter might be the important factor
in synaptic adaptation, the process by which the operating range
of the synapse adapts to increasing depolarizations of the
photoreceptor in increasing background light. Drugs known from
electrophysiological observations to interfere with synaptic
adaptation blocked the uptake of [3H]histamine into
photoreceptors. These drugs also blocked the sodium (Na)-triggered
efflux of [3H]histamine, previously loaded into
photoreceptors, via the histamine transporter. Several
lines of evidence showed that efflux of [3H]histamine
did not occur via calcium-dependent exocytosis. First,
efflux occurred when the preparation was bathed in calcium
(Ca)-free/EGTA salines or in cobalt (Co)-containing salines.
Even more importantly, efflux could be elicited from axons,
whose membranes must contain the transporter protein since they
take up [3H]histamine independently from the presynaptic
terminals. Since both adaptation and the histamine transporter
are blocked by the same agents, the transporter may underlie
adaptation by maintaining the cleft histamine concentration
in a particular range independent of light intensity. We also
characterized the transporter further and found that it is
partially dependent on chloride ions, and that neither
[3H]norepinephrine nor [3H]dopamine are
transported (at 20 μM), adding to evidence that the transporter
is highly selective for histamine.
Publisher
Cambridge University Press (CUP)
Subject
Sensory Systems,Physiology
Cited by
6 articles.
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