Activation of NMDA receptors linked to modulation of voltage-gated ion channels and functional implications.
Catfish (Ictalurus punctatus) cone horizontal cells contain N-methyl-d-aspartate (NMDA) receptors, the function of which has yet to be determined. In the present study, we have examined the effect of NMDA receptor activation on voltage-gated ion channel activity. NMDA receptor activation produced a long-term downregulation of voltage-gated sodium and calcium currents but had no effect on the delayed rectifying potassium current. NMDA's effect was eliminated in the presence of AP-7. To determine whether NMDA receptor activation had functional implications, isolated catfish cone horizontal cells were current clamped to mimic the cell's physiological response. When horizontal cells were depolarized, they elicited a single depolarizing overshoot and maintained a depolarized steady state membrane potential. NMDA reduced the amplitude of the depolarizing overshoot and increased the depolarized steady-state membrane potential. Both effects of NMDA were eliminated in the presence of AP-7. These results support the hypothesis that activation of NMDA receptors in catfish horizontal cells may affect the type of visual information conveyed through the distal retina.
Davis
S F
SF
Louisiana State University Health Sciences Center, Neuroscience Center of Excellence, New Orleans 70112, USA.
Linn
C L
CL
D000818:Animals; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000378:metabolism; D003035:Cobalt / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000378:metabolism*; D007059:Ictaluridae / Q000033:anatomy & histology / Q000378:metabolism*; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D016202:N-Methylaspartate / Q000494:pharmacology; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010775:Photic Stimulation; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects / Q000378:metabolism*; D012160:Retina / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology; D014785:Vision, Ocular / Q000187:drug effects / Q000502:physiology
D020746:Calcium Channels, L-Type; D018691:Excitatory Amino Acid Antagonists; D007473:Ion Channels; D016194:Receptors, N-Methyl-D-Aspartate; D015222:Sodium Channels; D003035:Cobalt; D018698:Glutamic Acid; D013779:Tetrodotoxin; D016202:N-Methylaspartate