Hypoxia-induced [(3)H]D-aspartate release from isolated bovine retina: modulation by calcium-channel blockers and glutamatergic agonists and antagonists.

Abstract

PURPOSE:

The aim of the present study was two-fold: (a) to examine the effect of hypoxia on [(3)H]D-aspartate release from isolated bovine and human retinae, and (b) to investigate the regulation of hypoxia-induced neurotransmitter release by glutamate receptor agonists and antagonists.

METHODS:

Isolated neural retinae were incubated in oxygenated Krebs buffer solution containing [(3)H]D-aspartate and then prepared for studies of neurotransmitter release using the superfusion method. Release of [(3)H]D-aspartate was evoked by K(+) (50 mM) applied at 90 minutes (S(1)) and hypoxia (induced by exposure of tissues to solutions pregassed with 95%N(2): 5% CO(2) for 60 minutes) at 108 minutes (S(2)) after onset of superfusion.

RESULTS:

Under hypoxic conditions, pO(2) in normal Krebs buffer solution was reduced from 14.53 +/- 0.26 ppm (n = 6) to 0.54 +/- 0.04 ppm (n = 9) after one hour of gassing with 95% N(2): 5% CO( 2). Exposure to hypoxia elicited an overflow of [(3)H]D-aspartate yielding S(2)/S(1) ratios of 0.62 +/- 0.06 (n = 12) and 0.54 +/- 0.03 (n = 8) in bovine and human tissues respectively. In isolated bovine retinae, L- and N-calcium-channel antagonists diltiazem, nitrendipine, verapamil and omega-conotoxin significantly (p < 0.01 or higher) attenuated hypoxia-induced [(3)H]D-aspartate release. L-glutamate (30 microM) significantly (p < 0.001) potentiated hypoxia-induced [(3)H]D-aspartate release whereas kainate (30 microM) inhibited this response. NMDA (in concentrations up to 1 mM) had no effect on hypoxia-induced [(3)H]D-aspartate release. Antagonists of glutamate receptors and the polyamine site on the NMDA receptor inhibited hypoxia-induced release of [(3)H]D-aspartate in bovine retina with the following rank order of activity: ifenprodil congruent with MCPG > L-AP3 > MK-801. At an equimolar concentration (10 microM), L-AP3 but not ifenprodil, MCPG, MK 801 or arcaine, caused a significant (p < 0.001) inhibition of hypoxia-induced [(3)H]D-aspartate release from human retinae.

CONCLUSIONS:

Hypoxia can induce the release of [( 3)H]D-aspartate from isolated bovine retinae by a calcium-dependent process. Hypoxia-induced [(3)H]D-aspartate release from isolated bovine retinae can be regulated by glutamate receptor agonists/antagonists and blockers of polyamine site on the NMDA receptor.

• Authors: S E Ohia, O S Awe, C A Opere, A M LeDay, L C Harris, N A Sharif
• Journal: Current eye research (Curr Eye Res) Vol. 23 Issue 5 Pg. 386-92 (Nov 2001) ISSN: 0271-3683 [Print] England
• PMID: 11910529 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Calcium Channel Blockers
• Excitatory Amino Acid Agonists
• Excitatory Amino Acid Antagonists
• Receptors, Neurotransmitter
• glutamine receptor
• D-Aspartic Acid
• Potassium

Topics

• Adult
• Aged
• Animals
• Calcium Channel Blockers (pharmacology)
• Cattle
• D-Aspartic Acid (metabolism)
• Excitatory Amino Acid Agonists (pharmacology)
• Excitatory Amino Acid Antagonists (pharmacology)
• Humans
• Hypoxia (metabolism)
• Middle Aged
• Potassium (pharmacology)
• Receptors, Neurotransmitter (metabolism)
• Retina (drug effects, metabolism)