Abstract
The transient receptor potential vanilloid 1 (TRPV1) channel is highly expressed in a subset of sensory neurons in the dorsal root ganglia (DRG) and trigeminal ganglia of experimental animals, responsible for nociception. Many researches have revealed that some TRPV1-positive neurons co-express the transient receptor potential ankyrin 1 (TRPA1) channel whose activities are closely modulated by TRPV1 channel. However, it is less investigated whether the activities of TRPV1 channel are modulated by the presence of TRPA1 channel in primary sensory neurons. This study clarified the difference in electrophysiological responses induced by TRPV1 channel activation between TRPA1-positive and TRPA1-negative DRG. TRPV1 and TRPA1 channel activations were evoked by capsaicin (1 μM), a TRPV1 agonist, and allyl isothiocyanate (AITC; 500 μM), a TRPA1 agonist, respectively. Capsaicin perfusion for 15 s caused a large inward current without a desensitization phase at a membrane potential of −70 mV in AITC-insensitive DRG (current density; 29.6 ± 5.6 pA/pF, time constant of decay; 12.8 ± 1.8 s). The capsaicin-induced currents in AITC-sensitive DRG had a small current density (12.7 ± 2.9 pA/pF) with a large time constant of decay (24.3 ± 5.4 s). In calcium imaging with Fura-2, the peak response by capsaicin was small and duration reaching the peak response was long in AITC-sensitive neurons. These electrophysiological differences were completely eliminated by HC-030031, a TRPA1 antagonist, in an extracellular solution or 10 mM EGTA, a Ca2+ chelator, in an internal solution. Capsaicin perfusion for 120 s desensitized the inward currents after a transient peak. The decay during capsaicin perfusion was notably slow in AITC-sensitive DRG; ratio of capsaicin-induced current 60 s after the treatment per the peak current in AITC-sensitive neurons (78 ± 9%) was larger than that in AITC-insensitive neurons (48 ± 5%). The capsaicin-induced current in the desensitization phase was attenuated by HC-030031 in AITC-insensitive DRG. These results indicate that (1) TRPV1-mediated currents in TRPA1-positive neurons characterize small current densities with slow decay, which is caused by TRPA1 channel activities and intracellular Ca2+ mobilization and (2) desensitization of TRPV1-mediated current in TRPA1-positive neurons is apparently slow, due to appending TRPA1-mediated current.
Highlights
Takayoshi Masuoka *, Makiko Kudo, Yuka Yamashita, Junko Yoshida, Noriko Imaizumi, Ikunobu Muramatsu, Matomo Nishio and Takaharu Ishibashi
We clarified the difference in kinetics of current responses to transient receptor potential vanilloid 1 (TRPV1) channel activation between transient receptor potential ankyrin 1 (TRPA1)-negative and TRPA1-positive dorsal root ganglia (DRG) neurons using whole-cell recording
TRPA1-negative and TRPA1positive DRG neurons were distinguished by responsiveness to perfusion of 500 μM allyl isothiocyanate (AITC) for 30 s, >5 min after capsaicin perfusion
Summary
Takayoshi Masuoka *, Makiko Kudo, Yuka Yamashita, Junko Yoshida, Noriko Imaizumi, Ikunobu Muramatsu, Matomo Nishio and Takaharu Ishibashi. Many researches have revealed that some TRPV1-positive neurons co-express the transient receptor potential ankyrin 1 (TRPA1) channel whose activities are closely modulated by TRPV1 channel. It is less investigated whether the activities of TRPV1 channel are modulated by the presence of TRPA1 channel in primary sensory neurons. The capsaicin-induced current in the desensitization phase was attenuated by HC-030031 in AITC-insensitive DRG These results indicate that (1) TRPV1-mediated currents in TRPA1-positive neurons characterize small current densities with slow decay, which is caused by TRPA1 channel activities and intracellular Ca2+ mobilization and (2) desensitization of TRPV1-mediated current in TRPA1-positive neurons is apparently slow, due to appending TRPA1-mediated current. We examined the differences in the kinetics of current responses induced by TRPV1 channel activation in TRPA1-positive and TRPA1-negative DRG neurons to elucidate the modulating effect of TRPA1 channels on TRPV1 channel activities
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