title: Distinct inhibition of voltage-activated Ca2+ channels by delta-opioid agonists in dorsal root ganglion neurons devoid of functional T-type Ca2+ currents.
abstract: Both mu- and delta-opioid agonists selectively inhibit nociception but have little effect on other sensory modalities. Voltage-activated Ca(2+) channels in the primary sensory neurons are important for the regulation of nociceptive transmission. In this study, we determined the effect of delta-opioid agonists on voltage-activated Ca(2+) channel currents (I(Ca)) in small-diameter rat dorsal root ganglion (DRG) neurons that do and do not bind isolectin B(4) (IB(4)). The delta-opioid agonists [d-Pen(2),d-Pen(5)]-enkephalin (DPDPE) and deltorphin II produced a greater inhibition of high voltage-activated I(Ca) in IB(4)-negative than IB(4)-positive neurons. Furthermore, DPDPE produced a greater inhibition of N-, P/Q-, and L-type I(Ca) in IB(4)-negative than IB(4)-positive neurons. However, DPDPE had no significant effect on the R-type I(Ca) in either type of cells. We were surprised to find that DPDPE failed to inhibit either the T-type or high voltage-activated I(Ca) in all the DRG neurons with T-type I(Ca). Double immunofluorescence labeling showed that the majority of the delta-opioid receptor-immunoreactive DRG neurons had IB(4) labeling, while all DRG neurons immunoreactive to delta-opioid receptors exhibited Cav(3.2) immunoreactivity. Additionally, DPDPE significantly inhibited high voltage-activated I(Ca) in Tyrode's or N-methyl-d-glucamine solution but not in tetraethylammonium solution. This study provides new information that delta-opioid agonists have a distinct effect on voltage-activated Ca(2+) channels in different phenotypes of primary sensory neurons. High voltage-activated Ca(2+) channels are more sensitive to inhibition by delta-opioid agonists in IB(4)-negative than IB(4)-positive neurons, and this opioid effect is restricted to DRG neurons devoid of functional T-type Ca(2+) currents.
authors.affiliation: Department of Anesthesiology and Pain Medicine, Unit 110, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA.
authors.forename: Z-Z
authors.initials: ZZ
authors.lastname: Wu
authors.forename: S-R
authors.initials: SR
authors.lastname: Chen
authors.forename: H-L
authors.initials: HL
authors.lastname: Pan
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020747:Calcium Channels, T-Type / Q000502:physiology*; D004307:Dose-Response Relationship, Radiation; D004347:Drug Interactions; D004558:Electric Stimulation / Q000379:methods; D020881:Enkephalin, D-Penicillamine (2,5)- / Q000494:pharmacology*; D005727:Ganglia, Spinal / Q000166:cytology*; D006023:Glycoproteins / Q000378:metabolism; D037102:Lectins / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000528:radiation effects; D009271:Naltrexone / Q000031:analogs & derivatives / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009433:Neural Inhibition / Q000187:drug effects*; D009475:Neurons, Afferent / Q000187:drug effects*; D009842:Oligopeptides / Q000494:pharmacology*; D018408:Patch-Clamp Techniques / Q000379:methods; D051381:Rats; D017207:Rats, Sprague-Dawley; D017465:Receptors, Opioid, delta / Q000378:metabolism; D053675:Versicans; D020866:omega-Conotoxin GVIA / Q000494:pharmacology
chemical_list: D000701:Analgesics, Opioid; C509958:Cacna1h protein, rat; D002121:Calcium Channel Blockers; D020747:Calcium Channels, T-Type; D006023:Glycoproteins; D037102:Lectins; D009292:Narcotic Antagonists; D009842:Oligopeptides; D017465:Receptors, Opioid, delta; C508324:Vcan protein, rat; C060209:deltorphin II, Ala(2)-; D053675:Versicans; D009271:Naltrexone; D020881:Enkephalin, D-Penicillamine (2,5)-; D020866:omega-Conotoxin GVIA; C055382:naltrindole