[Show abstract][Hide abstract] ABSTRACT: We have investigated the heterodimerization of ORL1 receptors and classical members of the opioid receptor family. All three
classes of opioid receptors could be co-immunoprecipitated with ORL1 receptors from both transfected tsA-201 cell lysate and
rat dorsal root ganglia lysate, suggesting that these receptors can form heterodimers. Consistent with this hypothesis, in
cells expressing either one of the opioid receptors together with ORL1, prolonged ORL1 receptor activation via nociceptin
application resulted in internalization of the opioid receptors. Conversely, μ-, δ-, and κ-opioid receptor activation with
the appropriate ligands triggered the internalization of ORL1. The μ-opioid receptor/ORL1 receptor heterodimers were shown
to associate with N-type calcium channels, with activation of μ-opioid receptors triggering N-type channel internalization,
but only in the presence of ORL1. Furthermore, the formation of opioid receptor/ORL1 receptor heterodimers attenuated the
ORL1 receptor-mediated inhibition of N-type channels, in part because of constitutive opioid receptor activity. Collectively,
our data support the existence of heterodimers between ORL1 and classical opioid receptors, with profound implications for
effectors such as N-type calcium channels.
[Show abstract][Hide abstract] ABSTRACT: N-type calcium channels are essential mediators of spinal nociceptive transmission. The core subunit of the N-type channel is encoded by a single gene, and multiple N-type channel isoforms can be generated by alternate splicing. In particular, cell-specific inclusion of an alternatively spliced exon 37a generates a novel form of the N-type channel that is highly enriched in nociceptive neurons and, as we show here, downregulated in a neuropathic pain model. Splice isoform-specific small interfering RNA silencing in vivo reveals that channels containing exon 37a are specifically required for mediating basal thermal nociception and for developing thermal and mechanical hyperalgesia during inflammatory and neuropathic pain. In contrast, both N-type channel isoforms (e37a- and e37b-containing) contribute to tactile neuropathic allodynia. Hence, exon 37a acts as a molecular switch that tailors the channels toward specific roles in pain.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 07/2007; 27(24):6363-73. DOI:10.1523/JNEUROSCI.0307-07.2007 · 6.34 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Calcium influx into presynaptic nerve terminals via voltage-gated Ca2+ channels is an essential step in neurotransmitter release. The predominant Ca2+ channel species in synaptic nerve terminals are P/Q-type and N-type channels, with their relative levels of expression varying across the nervous system. The different distributions of these two channel subtypes are reflected in their distinct physiological and pathological roles, yet their activity is regulated by common mechanisms and both function as part of larger signaling complexes that enable their precise regulation and subcellular targeting. Here, we provide a broad overview of molecular and cellular mechanisms that regulate Ca2+ channels, and how these cellular signaling pathways are integrated at the level of the channel protein.
Trends in Neurosciences 12/2006; 29(11):617-24. DOI:10.1016/j.tins.2006.08.006 · 13.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The inhibition of N-type calcium channels by opioid receptor like receptor 1 (ORL1) is a key mechanism for controlling the transmission of nociceptive signals. We recently reported that signaling complexes consisting of ORL1 receptors and N-type channels mediate a tonic inhibition of calcium entry. Here we show that prolonged ( approximately 30 min) exposure of ORL1 receptors to their agonist nociceptin triggers an internalization of these signaling complexes into vesicular compartments. This effect is dependent on protein kinase C activation, occurs selectively for N-type channels and cannot be observed with mu-opioid or angiotensin receptors. In expression systems and in rat dorsal root ganglion neurons, the nociceptin-mediated internalization of the channels is accompanied by a significant downregulation of calcium entry, which parallels the selective removal of N-type calcium channels from the plasma membrane. This may provide a new means for long-term regulation of calcium entry in the pain pathway.