Electrophysiology of glutamate and sodium co‐transport in a glial cell of the salamander retina.

Electrophysiology of glutamate and sodium co‐transport in a glial cell of the salamander retina. 1. Müller cells were isolated from salamander retinas and their membrane voltage was controlled with a whole‐cell voltage clamp. External D‐aspartate, L‐aspartate and L‐glutamate each induced a membrane current. D‐Glutamate, kainate, quisqualate and N‐methyl‐D‐aspartate were more than 100x less effective than L‐aspartate. Kynurenic acid had no effect on the current produced by L‐glutamate, L‐aspartate or D‐aspartate. 2. The current induced by an acidic amino acid (AAA) was completely dependent on the presence of external Na+. Neither Li+, Cs+, choline nor TEA+ were able to substitute for Na+. The relationship between external Na+ concentration and current amplitude can be explained if the binding of three Na+ ions enabled transport. The apparent affinity constant for Na+ binding was 41 mM. Altering K+, H+ and Cl‐ concentrations demonstrated that these ions are not required for transport. 3. The shape of the current‐voltage relation did not depend on the external amino acid concentration. The relationship between D‐aspartate concentration and current amplitude can be described by the binding of D‐aspartate to a single site with an apparent affinity constant of 20 microM. 4. Influx and efflux of AAA were not symmetric. Although influx was electrogenic, efflux did not produce a current. Moreover, influx stimulated efflux; but efflux inhibited influx. 5. Removing external Na+ demonstrated that Na+ carried a current in the absence of an AAA. Li+ was a very poor substitute for Na+. This current may be due to the uncoupled movement of Na+ through the transporter. The relationship between the external Na+ concentration and the amplitude of the uncoupled current can be explained if the binding of two or three Na+ ions enabled the translocation of Na+ in the absence of an AAA. The apparent affinity constant for Na+ binding was approximately 90 mM. 6. The temperature dependence of the AAA‐induced current had a Q10 between 8 and 18 degrees C of 1.95. The Q10 is consistent with a rate constant for influx of 10(4) s‐1 (at ‐70 mV and 20 degrees C). The maximum rate of influx was measured following a concentration jump produced by the photolysis of ‘caged’ L‐glutamate. The onset of the observed current was limited by the 1.3 ms resolution of the recording system. Hence, the rate constant for influx must be faster than 10(3) s‐1.(ABSTRACT TRUNCATED AT 400 WORDS) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of Physiology Wiley

Electrophysiology of glutamate and sodium co‐transport in a glial cell of the salamander retina.

The Journal of Physiology, Volume 426 (1) – Jul 1, 1990

Loading next page...
 
/lp/wiley/electrophysiology-of-glutamate-and-sodium-co-transport-in-a-glial-cell-QbsbUWHn0T
Publisher
Wiley
Copyright
© 2014 The Physiological Society
ISSN
0022-3751
eISSN
1469-7793
D.O.I.
10.1113/jphysiol.1990.sp018126
Publisher site
See Article on Publisher Site

Abstract

1. Müller cells were isolated from salamander retinas and their membrane voltage was controlled with a whole‐cell voltage clamp. External D‐aspartate, L‐aspartate and L‐glutamate each induced a membrane current. D‐Glutamate, kainate, quisqualate and N‐methyl‐D‐aspartate were more than 100x less effective than L‐aspartate. Kynurenic acid had no effect on the current produced by L‐glutamate, L‐aspartate or D‐aspartate. 2. The current induced by an acidic amino acid (AAA) was completely dependent on the presence of external Na+. Neither Li+, Cs+, choline nor TEA+ were able to substitute for Na+. The relationship between external Na+ concentration and current amplitude can be explained if the binding of three Na+ ions enabled transport. The apparent affinity constant for Na+ binding was 41 mM. Altering K+, H+ and Cl‐ concentrations demonstrated that these ions are not required for transport. 3. The shape of the current‐voltage relation did not depend on the external amino acid concentration. The relationship between D‐aspartate concentration and current amplitude can be described by the binding of D‐aspartate to a single site with an apparent affinity constant of 20 microM. 4. Influx and efflux of AAA were not symmetric. Although influx was electrogenic, efflux did not produce a current. Moreover, influx stimulated efflux; but efflux inhibited influx. 5. Removing external Na+ demonstrated that Na+ carried a current in the absence of an AAA. Li+ was a very poor substitute for Na+. This current may be due to the uncoupled movement of Na+ through the transporter. The relationship between the external Na+ concentration and the amplitude of the uncoupled current can be explained if the binding of two or three Na+ ions enabled the translocation of Na+ in the absence of an AAA. The apparent affinity constant for Na+ binding was approximately 90 mM. 6. The temperature dependence of the AAA‐induced current had a Q10 between 8 and 18 degrees C of 1.95. The Q10 is consistent with a rate constant for influx of 10(4) s‐1 (at ‐70 mV and 20 degrees C). The maximum rate of influx was measured following a concentration jump produced by the photolysis of ‘caged’ L‐glutamate. The onset of the observed current was limited by the 1.3 ms resolution of the recording system. Hence, the rate constant for influx must be faster than 10(3) s‐1.(ABSTRACT TRUNCATED AT 400 WORDS)

Journal

The Journal of PhysiologyWiley

Published: Jul 1, 1990

There are no references for this article.

You’re reading a free preview. Subscribe to read the entire article.


DeepDyve is your
personal research library

It’s your single place to instantly
discover and read the research
that matters to you.

Enjoy affordable access to
over 18 million articles from more than
15,000 peer-reviewed journals.

All for just $49/month

Explore the DeepDyve Library

Search

Query the DeepDyve database, plus search all of PubMed and Google Scholar seamlessly

Organize

Save any article or search result from DeepDyve, PubMed, and Google Scholar... all in one place.

Access

Get unlimited, online access to over 18 million full-text articles from more than 15,000 scientific journals.

Your journals are on DeepDyve

Read from thousands of the leading scholarly journals from SpringerNature, Elsevier, Wiley-Blackwell, Oxford University Press and more.

All the latest content is available, no embargo periods.

See the journals in your area

DeepDyve

Freelancer

DeepDyve

Pro

Price

FREE

$49/month
$360/year

Save searches from
Google Scholar,
PubMed

Create folders to
organize your research

Export folders, citations

Read DeepDyve articles

Abstract access only

Unlimited access to over
18 million full-text articles

Print

20 pages / month

PDF Discount

20% off