Analgesic transient receptor potential vanilloid‐1‐active compounds inhibit native and recombinant T‐type calcium channels

Abstract

Background and Purpose T‐type calcium (Cav3) and transient receptor potential vanilloid‐1 (TRPV1) channels play central roles in the control of excitability in the peripheral nervous system and are regarded as potential therapeutic pain targets. Modulators that either activate or inhibit TRPV1‐mediated currents display analgesic properties in various pain models despite opposing effects on their connate target, TRPV1. We explored the effects of TRPV1‐active compounds on Cav3‐mediated currents. Experimental Approach Whole‐cell patch clamp recordings were used to examine the effects of TRPV1‐active compounds on rat dorsal root ganglion low voltage‐activated calcium currents and recombinant Cav3 isoforms in expression systems. Key Results The classical TRPV1 agonist capsaicin as well as TRPV1 antagonists A‐889425, BCTC, and capsazepine directly inhibited Cav3 channels. These compounds altered the voltage‐dependence of activation and inactivation of Cav3 channels and delayed their recovery from inactivation, leading to a concomitant decrease in T‐type current availability. The TRPV1 antagonist capsazepine potently inhibited Cav3.1 and 3.2 channels (KD < 120 nM), as demonstrated by its slow off rate. In contrast, neither the TRPV1 agonists, Palvanil and resiniferatoxin, nor the TRPV1 antagonist AMG9810 modulated Cav3‐mediated currents. Conclusions and Implications Analgesic TRPV1‐active compounds inhibit Cav3 currents in native and heterologous systems. Hence, their analgesic effects may not be exclusively attributed to their actions on TRPV1, which has important implications in the current understanding of nociceptive pathways. Importantly, our results highlight the need for attention in the experimental design used to address the analgesic properties of Cav3 channel inhibitors.

Molecular and Functional Characterization of Neurogenin-2 Induced Human Sensory Neurons

“…The magnitude of LVA currents in NGN2 iSNs and the relatively low abundance of TRPV1 signal detected (immunofluorescence and qPCR) here suggest a parallel between our cultures and previously described subpopulations of capsaicin insensitive DRG and trigeminal neurons from adult mice (Pearce and Duchen, 1994;Borgland et al, 2001;Fioretti et al, 2011). It is of note, however, that capsaicin inhibits LVA calcium channels indirectly via calcium influx through TRPV1 (Comunanza et al, 2011) in DRG neurons and in HEK293 cells co-expressing Cav3.1 and TRPV1 (McArthur et al, 2019). Furthermore, capsaicin also directly inhibits all T-type channel isoforms with IC 50 s ∼20 µM (McArthur et al, 2019) thus suggesting that the magnitude of T-type calcium currents may be underestimated in the presence of capsaicin.…”

“…It is of note, however, that capsaicin inhibits LVA calcium channels indirectly via calcium influx through TRPV1 (Comunanza et al, 2011) in DRG neurons and in HEK293 cells co-expressing Cav3.1 and TRPV1 (McArthur et al, 2019). Furthermore, capsaicin also directly inhibits all T-type channel isoforms with IC 50 s ∼20 µM (McArthur et al, 2019) thus suggesting that the magnitude of T-type calcium currents may be underestimated in the presence of capsaicin.…”

Spider Venom Peptide Pn3a Inhibition of Primary Afferent High Voltage-Activated Calcium Channels

“…Pore blocking Na v channel toxins cross-react with other targets, include tetrodotoxin (Na v /Ca v ), saxitoxin (Na v /K v /Ca v ) and µ -conotoxin PIIIA (Na v /K v /Na v Bac) ( McArthur et al, 2011 ; Leipold et al, 2017 ; Finol-Urdaneta et al, 2019 ); whereas voltage-sensing domain (VSD) gating modifier toxins like ProTxI (Na v /K v /Ca v /TRPA1) ( Middleton et al, 2002 ; Bosmans et al, 2008 ; Bladen et al, 2014 ; Gui et al, 2014 ), ProTxII (Na v /Ca v ) ( Middleton et al, 2002 ; Bladen et al, 2014 ), kurtoxin (Na v /Ca v ) ( Chuang et al, 1998 ), Hanatoxin (K v /Na v /Ca v ) ( Swartz and MacKinnon, 1995 ; Li-Smerin and Swartz, 1998 ; Bosmans et al, 2008 ), and JZTX-I (Na v /K v ) ( Xiao et al, 2005 ; Yuan et al, 2007 ). Furthermore, small molecule compounds modulating VSDs include capsaicin, and capsazepine (TRPV1/K v /Ca v ) ( Kuenzi and Dale, 1996 ; Caterina et al, 1997 ; McArthur et al, 2019 ) to name a few.…”

Inhibition of transient receptor potential vanilloid type 1 through α₂ adrenergic receptors at peripheral nerve terminals relieves pain

“…Although, we could not find inhibitory effects of JNJ-17203212 on thermal and formalin responses, unfortunately, nociceptive behaviors induced by noxious heat and formalin were inhibited by capsazepine, suggesting a possibility that TRPV1 activation was involved in the nociceptive behaviors evoked by these stimuli. However, since capsazepine has been reported to have inhibitory effects on other molecules, such as low voltage-activated Ca 2+ channels [ 20 ] and HCN channels [ 28 ], we cannot exclude the possibility that nonspecific effects of capsazepine contribute to inhibition of these nociceptive responses to heat and formalin. In the capsaicin test, the inhibitory action of clonidine was reversed by yohimbine.…”