Hypoxia-induced [(3)H]D-aspartate release from isolated bovine retina: modulation by calcium-channel blockers and glutamatergic agonists and antagonists.
OBJECTIVE
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.
Ohia
S E
SE
Department of Pharmacy Sciences, School of Pharmacy and Allied Health Professions, Creighton University, Omaha, NE 68178, USA. seohia@creighton.edu
Awe
O S
OS
Opere
C A
CA
LeDay
A M
AM
Harris
L C
LC
Sharif
N A
NA
D000328:Adult; D000368:Aged; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002417:Cattle; D026603:D-Aspartic Acid / Q000378:metabolism*; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology*; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D006801:Humans; D000860:Hypoxia / Q000378:metabolism*; D008875:Middle Aged; D011188:Potassium / Q000494:pharmacology; D017981:Receptors, Neurotransmitter / Q000378:metabolism*; D012160:Retina / Q000187:drug effects / Q000378:metabolism*
D002121:Calcium Channel Blockers; D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; D017981:Receptors, Neurotransmitter; C069474:glutamine receptor; D026603:D-Aspartic Acid; D011188:Potassium