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A functional link between T‐type calcium channels and μ‐opioid receptor expression in adult primary sensory neurons
Author(s) -
Wu ZiZhen,
Cai YouQing,
Pan HuiLin
Publication year - 2009
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.2009.06014.x
Subject(s) - sensory system , neuroscience , link (geometry) , t type calcium channel , receptor , voltage dependent calcium channel , biology , calcium , medicine , computer science , genetics , computer network
J. Neurochem . (2009) 109 , 867–878. Abstract The μ‐opioid receptor agonists have a preferential effect on nociception in adults but their analgesic effect is less selective in neonates. Here we presented our finding that the μ‐opioid receptor agonists had no effect on high voltage‐activated Ca 2+ channels (HVACCs) in adult dorsal root ganglion (DRG) neurons that exhibited a prominent T‐type Ca 2+ current. We also determined the mechanisms underlying the μ‐opioid agonists’ lack of effect on HVACCs in these neurons. The μ‐opioid agonist [ d ‐Ala 2 , N ‐Me‐Phe 4 ,Gly‐ol 5 ]‐enkephalin (DAMGO), morphine, and morphine 6‐β‐D‐glucuronide had no effect on either T‐type or HVACC currents despite the presence of a large N‐type Ca 2+ current in neurons with T‐type Ca 2+ currents. DAMGO still had no effect on HVACC currents when T‐type Ca 2+ channels were blocked in these neurons. However, intracellular dialysis of GTP‐γ‐S to activate G proteins significantly attenuated HVACC currents. DRG neurons with T‐type Ca 2+ currents showed little responses to capsaicin. Single‐cell RT‐PCR analysis revealed that the μ‐opioid receptor mRNA was present only in adult DRG neurons lacking prominent T‐type Ca 2+ currents. In the neonatal DRG, DAMGO inhibited HVACC currents in 31% neurons with T‐type Ca 2+ currents. The μ‐opioid receptor mRNA was detected in all neurons without T‐type Ca 2+ currents and also in 28.6% of neurons with T‐type Ca 2+ currents in the neonatal DRG. Our study provides novel information that adult DRG neurons with prominent T‐type Ca 2+ currents do not express μ‐opioid receptors. Expression of T‐type Ca 2+ (Ca V 3.2) channels and μ‐opioid receptors may be developmentally co‐regulated as some DRG neurons differentiate toward becoming nociceptive neurons.