Intracellular ATP Increases Capsaicin-Activated Channel Activity by Interacting with Nucleotide-Binding Domains

Abstract

Capsaicin (CAP)-activated ion channel plays a key role in generating nociceptive neural signals in sensory neurons. Here we present evidence that intracellular ATP upregulates the activity of capsaicin receptor channel. In inside-out membrane patches isolated from sensory neurons, application of CAP activated a nonselective cation channel (i cap ). Further addition of ATP to the bath caused a significant increase in i cap , with a K 1/2 of 3.3 mM. Capsaicin (CAP), the pungent ingredient of hot peppers, excites small sensory neurons and thereby causes pain or neurogenic inflammation (Bevan and Szolcsanyi, 1990;Szallasi and Blumberg, 1999). In cultured dorsal root ganglion (DRG) neurons, CAP has been shown to activate a nonselective cation channel and produce influx of cations (Bevan and Szolcsanyi, 1990;Oh et al., 1996). The activation of this cation channel is probably responsible for the excitation of a group of sensory neurons. A cDNA, vanilloid receptor 1 (VR1), that encodes a channel sensitive to CAP has recently been cloned (Caterina et al., 1997). A striking property of VR1 is that it is also activated by heat (Caterina et al., 1997;Tominaga et al., 1998). Another interesting property of VR1 is its activation by acid, indicating that protons can activate the channel (Tominaga et al., 1998). It is now known that disruption of VR1 gene reduces inflammation-induced heat hyperalgesia (Caterina et al., 2000;Davis et al., 2000). As a result, the view of the CAP receptor as a potential nociceptive heat and chemical sensor has gained a wide acceptance (Kress and Zeilhofer, 1999;Szallasi and Blumberg, 1999;Caterina et al., 2000;Davis et al., 2000).Recently, endogenous lipids such as anandamide and various metabolic products of lipoxygenases such as 12-hydroperoxyeicosatetraenoic acid and leukotriene B 4 have been shown to activate the CAP channel (Zygmunt et al., 1999;Hwang et al., 2000). The three-dimensional structure of 12-hydroperoxyeicosatetraenoic acid, one of the lipoxygenase products, was found to superimpose reasonably well with that of capsaicin, suggesting that these lipids may potentially act as endogenous capsaicin-like substances (Hwang et al., 2000).During the course of our studies on the CAP channel, we observed that the channel activity in the cell-attached state with CAP in the pipette is always significantly higher than that after formation of the inside-out state. This difference in channel activity could not be explained by a change in membrane potential or ionic composition. Therefore, we speculated that there exists a cytosolic substance that helps to maintain the channel activity at a higher level and that its washout reduces channel activity. Activity of many ion channels is often modulated by phosphorylation (Levitan, 1994). For example, activity of large conductance Ca 2ϩ -activated K ϩ channel in the brain increases after the addition of ATP via phosphorylation mediated by cAMP-dependent protein kinase A (PKA) (Baraban et al., 1985;Chung et al., 1991) or protein kinase C (PKC) (De Peyer ...

Phospholipase C Mediated Modulation of TRPV1 Channels

“…ATP has been shown to bind to the C-terminal "walker motif" of TRPV1 and enhance currents induced by 1 μM capsaicin in excised patches (35). The effect of ATP was independent of protein or lipid phosphorylation, as non-hydrolyzable analogues and ATP in the absence of Mg 2+ had similar effects.…”

Interaction between vanilloid receptors and purinergic metabotropic receptors: Pain perception and beyond

“…It is also possible that two different agonists acting on separate signaling pathways can achieve a similar response. It is worth noting that in a recent study intracellular ATP binding to a Walker-type nucleotide-binding domain sensitized the VR response to capsaicin, suggesting that ATP could function as a coagonist in a fashion similar to glycine acting on the N-methyl-Daspartate receptor (19).…”

Biophysical characterization of the isolated C‐terminal region of the transient receptor potential vanilloid 1

“…The cytosolic C-terminal domain of the TRPV1 (C-TRPV1) possesses two distinct regions, namely, the TRP domain, comprising residues 684-721, and a regulatory region, consisting of amino acids 767-810, being both connected by a flexible linker [13,16,17]. The C terminus has been proposed to include the temperature sensor activity (specifically in the linker segment (amino acids 727-752) [18,19]), tubulin-interacting modules [20] and phosphorylation sites [21]. The TRP domain of the C-TRPV1 has been defined as an association domain involved in the tetramerization of the TRPV1 channel subunits into functional channels [13].…”