Evoked GABA release is not mediated by N-type VDCC in the frontal cortex of awake rats: effects of neomycin.
The purpose of the present study was to analyze the Ca2+ channel involved in GABA release under resting and K(+)-evoked conditions in vivo. We used microdialysis to investigate the effects of the voltage-dependent calcium channel (VDCC) blockers neomycin, kanamycin, and omega-conotoxin GVIA, and the voltage-dependent Na+ channel blocker tetrodotoxin, in the frontal cortex of awake rats. The GABA content in frontal dialysates was analyzed by high performance liquid chromatography coupled to fluorescence detection. Basal GABA release was kanamycin, omega-conotoxin, and tetrodotoxin resistant, whereas neomycin induced a significant increase from the basal level. The K(+)-evoked release of GABA was kanamycin and omega-conotoxin resistant, but tetrodotoxin sensitive. The effects of neomycin were masked by the action of this drug on basal release. These results suggest that neomycin may affect GABA release in the frontal cortex through a mechanism independent of VDCC. In addition, the K(+)-evoked release of GABA in this cortical area was not mediated by the N-type voltage-dependent calcium channels, but was dependent on neural activity or TTX sensitive.
Martínez-Martos
J M
JM
Department of Biochemistry, F. Oloriz Institute of Neurosciences, School of Medicine, University of Granada, Spain.
Iribar
M C
MC
Peinado
J M
JM
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002851:Chromatography, High Pressure Liquid; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D007612:Kanamycin / Q000494:pharmacology; D008297:Male; D017551:Microdialysis; D009355:Neomycin / Q000494:pharmacology*; D010455:Peptides / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D017397:Prefrontal Cortex / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism; D013779:Tetrodotoxin / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*; D020866:omega-Conotoxin GVIA
D000900:Anti-Bacterial Agents; D002121:Calcium Channel Blockers; D004791:Enzyme Inhibitors; D010455:Peptides; D015222:Sodium Channels; D013779:Tetrodotoxin; D005680:gamma-Aminobutyric Acid; D007612:Kanamycin; D020866:omega-Conotoxin GVIA; D009355:Neomycin; D011188:Potassium