Tonic transmitter release in a graded potential synapse.
Uusitalo, Raimo O., Mikko Juusola, Eero Kouvalainen and Matti Weckstrom.
Department of Physiology, University of Oulu, Oulu, Finland.
APStracts 2:0122N, 1995.
SUMMARY AND CONCLUSIONS
1. We studied graded synaptic transmission in the fly photoreceptor-
interneuron synapse by using intracellular in situ recordings from pre- and
post-synaptic cells. 2. A large pre-synaptic hyperpolarization after light
adaptation, caused by the activation of the electrogenic Na + /K + -pump,
drastically reduced the conspicuous post-synaptic dark noise. In the same time
the post-synaptic neurons depolarized with an increase of the input resistance
by 5 to 10 M[omega]. 3. The spectral characteristics of the post-
synapticmembrane noise in dark and during noise reduction, together with the
other results, suggested that the transmitter release decreased dramatically
ca. 12 mV below the resting potential of the pre-synaptic photoreceptors. 4.
During the post-synaptic noise reduction the saturated and subsaturated LMC
responses were increased up to 9 ? mV with a time constant of recovery of
about 10 s. This increase was shown to be caused by the negative shift of the
reversal potential of the transmitter-gated (mainly Cl - ) conductance, caused
apparently by the reduced transmitter input. 5. The results strongly suggest
that the photoreceptor transmitter release in fly is tonic, even in dark, and
further support the modulation of the synaptic voltage transfer by
postsynaptic Cl - -extrusion.
Received 18 November 1994; accepted in final form 3 April 1995.
APS Manuscript Number J729-4.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 1 May 1995.