Calcium-dependent inhibition of T-type calcium channels by TRPV1 activation in rat sensory neurons

Abstract

We studied the inhibitory effects of transient receptor potential vanilloid-1 (TRPV1) activation by capsaicin on low-voltage-activated (LVA, T-type) Ca 2+ channel and highvoltage-activated (HVA; L, N, P/Q, R) currents in rat DRG sensory neurons, as a potential mechanism underlying capsaicin-induced analgesia. T-type and HVA currents were elicited in whole-cell clamped DRG neurons using ramp commands applied before and after 30-s exposures to 1 μM capsaicin. T-type currents were estimated at the first peak of the I-V characteristics and HVA at the second peak, occurring at more positive potentials. Small and medium-sized DRG neurons responded to capsaicin producing transient inward currents of variable amplitudes, mainly carried by Ca 2+. In those cells responding to capsaicin with a large Ca 2+ influx (59% of the total), a marked inhibition of both T-type and HVA Ca 2+ currents was observed. The percentage of T-type and HVA channel inhibition was prevented by replacing Ca 2+ with Ba 2+ during capsaicin application or applying high doses of intracellular BAPTA (20 mM), suggesting that TRPV1-mediated inhibition of T-type and HVA channels is Ca 2+ -dependent and likely confined to membrane nanomicrodomains. Our data are consistent with the idea that TRPV1-induced analgesia may derive from indirect inhibition of both T-type and HVA channels which, in turn, would reduce the threshold of nociceptive signals generation (T-type channel inhibition) and nociceptive synaptic transmission (HVA-channels inhibition).

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

“…Previous studies have described T‐type Ca 2+ current inhibition by low doses of TRPV1‐agonists in DRG neurons (Comunanza et al, ; Kerckhove et al, ). In the present study, this observation was verified and expanded in detail through co‐expression experiments of TRPV1 and Ca v 3.1 in HEK293 cells.…”

“…Furthermore, differential effects of other TRPV1‐active molecules like Palvanil, resiniferatoxin, or AMG9810 that were unable to modulate Ca v 3 function can rule out major endogenous TRPV1‐mediated effect in our heterologous system. Previous studies have described irreversible T‐type Ca 2+ current inhibition by low concentrations of TRPV1‐agonists in DRG neurons (Comunanza et al, ; Kerckhove et al, ). In this study, we show that this inhibition depends strictly on Ca 2+ , likely via Ca 2+ entry through capsaicin‐activated TRPV1 triggering intracellular feedback mechanisms as proposed elsewhere (Cazade et al, ; Comunanza et al, ; Kerckhove et al, ).…”

“…Previous studies have described irreversible T‐type Ca 2+ current inhibition by low concentrations of TRPV1‐agonists in DRG neurons (Comunanza et al, ; Kerckhove et al, ). In this study, we show that this inhibition depends strictly on Ca 2+ , likely via Ca 2+ entry through capsaicin‐activated TRPV1 triggering intracellular feedback mechanisms as proposed elsewhere (Cazade et al, ; Comunanza et al, ; Kerckhove et al, ). Therefore, in tissues where TRPV1 and Ca v 3 channels coexist, low concentrations of TRPV1 activators (AM404 and capsaicin) irreversibly decrease T‐type current by a TRPV1‐mediated intracellular Ca 2+ increase.…”

“…However, many reports have been based on native low voltage-activated (LVA) calcium currents without expression system verification, and therefore, a direct effect of these compounds over Ca v 3-mediated currents is missing. It has been suggested that the modulation of LVA and high voltage-activated calcium currents in DRG neurons induced by a lowconcentration capsaicin occurs via a TRPV1-mediated mechanism (Comunanza, Carbone, Marcantoni, Sher, & Ursu, 2011;Kerckhove et al, 2014;Wu, Chen, & Pan, 2005). This has recently been shown to occur via an intracellular calcium-dependent mechanism (Cazade, Bidaud, Lory, & Chemin, 2017;Comunanza et al, 2011), leading to inhibition of Ca v 3-mediated currents, caused by the influx of Ca 2+ through activated TRPV1.…”

Phosphoinositide signaling in somatosensory neurons

“…The role of phosphoinositide depletion however was not examined in either of these cases. There are several reports showing that capsaicin inhibits VGCC in TRPV1 positive DRG neurons (Bleakman et al, 1990; Hagenacker et al, 2005; Wu et al, 2005, 2006) (Docherty et al, 1991; Comunanza et al, 2011), but the role of phosphoinositide signaling was not examined in any of the papers. Given the clear dependence of N-type channels on PI(4,5)P 2 and the robust depletion of PI(4,5)P 2 induced by TRPV1 activation (Lukacs et al, 2013b) this mechanism is feasible, at least for inhibition of N-type channels.…”