Journal of Neuroscience, Vol 12, 4234-4242, Copyright © 1992 by Society for Neuroscience
Energy requirements of glutamatergic pathways in rabbit retina
A Ames 3d and YY Li
Neurosurgical Service, Massachusetts General Hospital, Boston 02114.
In vitro rabbit retina was used as an example of CNS tissue in experiments
designed to measure the energy requirements associated with the activation
of different types of glutamate receptors. Retinas were exposed to
glutamate and to four analogs: kainate, 2-amino-4- phosphonobutyric acid
(APB), 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), and
2-amino-5-phosphonovaleric acid (APV). The changes in O2 consumption and
lactate production were determined using a recently developed experimental
system that permitted simultaneous measurements of the rates at which O2
was removed from the medium and acid was added. The glutamatergic agents
had relatively little effect on oxidative metabolism, but they caused large
changes in glycolysis. Kainate increased retinal lactate production by 50%,
whereas APB, CNQX, and APV reduced it by 23%, 19%, and 35%, respectively.
Glutamate increased lactate production by 16% when administered after APB,
but decreased it by 12% when administered after CNQX. The changes in energy
metabolism coincided with changes in electrophysiological function. Since
the energy metabolism of many retinal cells was presumably not much
affected by the glutamatergic agents, the changes measured as a percent of
total retinal glycolysis must have reflected considerably larger fractional
changes in the cells most affected. From the response to inhibitors, it
seems probable that even under resting conditions in darkness, activity in
glutamatergic pathways is responsible for more than 50% of the
glycolytically derived energy used by the cells involved. It also seems
probable (particularly from the response to kainate) that under some
circumstances the cells' energy metabolism and/or transport capability
cannot meet the requirements imposed by glutamate-induced increases in
function.(ABSTRACT TRUNCATED AT 250 WORDS)