Activation of NMDA receptors linked to modulation of voltage-gated ion channels and functional implications

• Published in: American Journal of Physiology: Cell Physiology 2003-03, Vol.284 (3), p.C757-C768
• Main Authors: Davis, S. F, Linn, C. L
• Format: Article
• Language: English
• Subjects: Animals; Calcium Channels, L-Type - drug effects; Calcium Channels, L-Type - metabolism; Cobalt - pharmacology; Excitatory Amino Acid Antagonists - pharmacology; Glutamic Acid - metabolism; Ictaluridae - anatomy & histology; Ictaluridae - metabolism; Ion Channels - drug effects; Ion Channels - metabolism; Membrane Potentials - drug effects; Membrane Potentials - physiology; N-Methylaspartate - pharmacology; Neurons - cytology; Neurons - drug effects; Neurons - metabolism; Photic Stimulation; Reaction Time - drug effects; Reaction Time - physiology; Receptors, N-Methyl-D-Aspartate - drug effects; Receptors, N-Methyl-D-Aspartate - metabolism; Retina - cytology; Retina - drug effects; Retina - metabolism; Sodium Channels - drug effects; Sodium Channels - metabolism; Synaptic Transmission - drug effects; Synaptic Transmission - physiology; Tetrodotoxin - pharmacology; Vision, Ocular - drug effects; Vision, Ocular - physiology
• ISSN: 0363-6143; 1522-1563
• DOI: 10.1152/ajpcell.00252.2002

1  Louisiana State University Health Sciences Center, Neuroscience Center of Excellence, New Orleans, Louisiana 70112; and 2  Western Michigan University, Department of Biological Sciences, Kalamazoo, Michigan 49008 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. neuromodulation; excitatory amino acid; sensory system; ionotropic; patch-clamp technique