Inhibition of human recombinant T-type calcium channels by N-arachidonoyl 5-HT

Background and purpose: N-arachidonoyl 5-HT (NA-5HT) has anti-nociceptive effects reported to be mediated by inhibitory actions at the transient receptor potential vanilloid receptor 1 (TRPV1) and fatty acid amide hydrolase (FAAH). Anandamide and N-arachidonoyl dopamine (NA-DA), endocannabinoids that activate TRPV1 or are metabolized by FAAH, also inhibit T-type calcium channels (/Ca). T-type /Ca are expressed by many excitable cells, including neurons involved in pain detection and processing. We sought to determine whether NA-5HT also modulates T-type /Ca. Experimental approach: Human recombinant T-type /Ca (Ca⌄3 channels) expressed in HEK 293 cells were examined using standard whole-cell voltage-clamp electrophysiology techniques. Key results: NA-5HT completely inhibited Ca⌄3 channels with a rank order of potency (pEC₅₀) of Ca⌄3.1(7.4)>Ca⌄3.3(6.8)≥Ca⌄3.2 (6.6). The effects of NA-5HT were voltage-dependent, and it produced significant hyperpolarizing shifts in Ca⌄3 steady-state inactivation relationships. NA-5HT selectively affected Ca⌄3.3 channel kinetics. Conclusions and implications: NA-5HT increases the steady-state inactivation of Ca⌄3 channels, reducing the number of channels available to open during depolarization. These effects occur at NA-5HT concentrations at or below those at which NA-5HT affects TRPV1 receptors and FAAH. NA-5HT is one of the most potent inhibitors of T-type /Ca described to date, and it is likely to exert some of its biological effects, including anti-nociception, via inhibition of these channels.13 page(s