NMDA enhances a depolarization-activated inward current in subthalamic neurons.
Previous studies have shown that N-methyl-D-aspartate (NMDA) receptor stimulation evokes Ca2+- and Na+-dependent burst firing in subthalamic nucleus (STN) neurons. Using whole-cell patch pipettes to record currents under voltage-clamp, we identified a time-dependent depolarization-activated inward current (DIC) that may underlie NMDA-induced burst firing in STN neurons in rat brain slices. Continuous superfusion with NMDA (20 microM) elicited a marked TTX-insensitive inward current when the membrane was depolarized to the level of -70 or -50 mV, from a holding potential of -100 mV. This current had a long duration, and its peak amplitude occurred at a test potential of -60 mV. DIC could not be evoked using the non-NMDA receptor agonist D,L-alpha-amino-3-hydroxy-5-methylisoxalone-4-propionic acid (AMPA). DIC was blocked by either intracellular BAPTA or by removal of extracellular Ca2+, but selective blockers of T-type (mibefradil), L-type (nifedipine) and N-type (omega-conotoxin GVIA) Ca2+ channels did not. Perfusing slices with a low extracellular concentration of sodium abolished the NMDA-induced DIC, implying that both Ca2+ and Na+ are necessary for the expression of DIC. Transient receptor potential (TRP) channel blockers flufenamic acid and SKF96365 severely reduced DIC amplitude, whereas NMDA-gated currents were either increased or were unchanged. These results suggest that the activation of NMDA receptors enhances a Ca2+-activated non-selective cation current that may be mediated by a member of the TRP channel family in STN neurons.
Department of Neurology, Oregon Health & Science University, Portland, OR 97239, USA.
Zi-Tao
ZT
Zhu
Adam
A
Munhall
Ke-Zhong
KZ
Shen
Steven W
SW
Johnson
D000818:Animals; D002118:Calcium / Q000502:physiology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004594:Electrophysiology; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology*; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D007473:Ion Channels / Q000187:drug effects; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D016202:N-Methylaspartate / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects*; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism; D020530:Subthalamus / Q000166:cytology / Q000187:drug effects / Q000502:physiology*
D002121:Calcium Channel Blockers; D002614:Chelating Agents; D018690:Excitatory Amino Acid Agonists; D007473:Ion Channels; D016194:Receptors, N-Methyl-D-Aspartate; D015222:Sodium Channels; D004533:Egtazic Acid; D016202:N-Methylaspartate; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium