A Persistent Na+ Conductance in Medium-Sized Neostriatal Neurons:
Characterization Using Infrared Videomicroscopy and Whole-cell Patch Clamp
Recordings.
Cepeda, Carlos, Scott H. Chandler, Lincoln W. Shumate and Michael S. Levine.
Mental Retardation Research Center and Department of Physiological Science,
University of California, Los Angeles, Los Angeles, CA 90024-1759.
APStracts 2:0186N, 1995.
SUMMARY AND CONCLUSIONS
1. The present study investigated the expression of a persistent Na +
conductance (I NaP ) in identified medium-sized neostriatal neurons. Nomarski
optics and infrared videomicroscopy were used for cell visualization and
identification in thick slices (350 Nm). Current and voltage clamp recordings
were obtained utilizing whole-cell patch clamp methodology. 2. Application of
depolarizing ramp voltage commands from a holding potential of -70 mV induced
a slow, non-inactivating inward current that occurred prior to and independent
of the rapidly inactivating sodium current that subserves action potential
generation. I NaP began to activate at potentials less negative than -70 mV
and peaked at -34 +/- 1 mV. Its average peak amplitude was -100 +/- 17 pA. I
NaP was abolished by tetrodotoxin (TTX, 0.5-1 NM) or a Na + free solution. In
contrast, it was not affected by Ca 2+ channel blockers. Depolarizing ramp
commands also induced tetraethylammonium (TEA) sensitive outward currents. 3.
Dopamine (DA) (20-100 NM) produced a significant reduction of I NaP . 4. These
results demonstrate the existence of a TTX-sensitive persistent Na +
conductance in medium-sized neostriatal neurons. This conductance is modulated
by DA and could play a role in the generation of rhythmic oscillations and in
supporting repetitive firing.
Received 27 March 1995; accepted in final form 16 June 1995.
APS Manuscript Number J200-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 18 July 1995.