Journal
PAIN
Volume 109, Issue 3, Pages 443-452Publisher
LIPPINCOTT WILLIAMS & WILKINS
DOI: 10.1016/j.pain.2004.02.021
Keywords
calcium imaging; glutamate receptor channel; glutamate receptor subtype; NMDA receptor; NMDA receptor antagonist; NMDA receptor channel; primary afferent neuron; whole cell patch clamp
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Funding
- NIDDK NIH HHS [P50 DK64539-01, R01 DK58173] Funding Source: Medline
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In the peripheral nervous system, N-methyl-D-aspartate receptors (NMDAR) expressed on the central and peripheral terminals of primary afferent neurons are involved in nociception. We used single cell imaging of intracellular calcium concentration ([Ca2+](i)) and patch clamp techniques to characterize the functional properties of NMDARs on adult rat dorsal root ganglia (DRG) neurons in primary culture and selectively on those innervating the distal colon. In Mg2+-free extracellular solution, rapid perfusion of DRG neurons with 250 muM NMDA and 10 muM glycine caused a significant increase in [Ca2+](j), and elicited inward currents in whole cell patch clamp recordings when the holding potential was - 60 mV. Both effects were reversibly inhibited by 200 muM ketamine in a use-dependent manner. The EC50 values for NMDA and glycine were 64 and 1.9 muM with Hill slope coefficients of 1.4 and 1.3, respectively. At negative potentials, extracellular Mg2+ blocked currents in a concentration- and voltage-dependent manner. The IC50 for Mg2+ at a holding potential of - 100 mV was 2.0 muM. The NMDAR subtype-selective antagonist, ifenprodil, inhibited 94% of the NMDA and glycine-induced cur-rent with an IC50 of 2.6 muM. There was no evidence of multiple binding sites for ifenprodil. There was no significant difference in the NMDAR current density on DRG neurons that had innervated the colon, nor was there a difference in the EC50 for ifenprodil. These results demonstrate that functional NMDARs expressed by DRG neurons innervating both somatic and visceral tissues of adult rats are composed predominantly of NR2B subunits. (C) 2004 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.
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