Background and purpose:
N-arachidonoyl dopamine (NADA) has complex effects on nociception mediated via cannabinoid CB1 receptors and the transient receptor potential vanilloid receptor 1 (TRPV1). Anandamide, the prototypic CB1/TRPV1 agonist, also inhibits T-type voltage-gated calcium channel currents (ICa). These channels are expressed by many excitable cells, including neurons involved in pain detection and processing. We sought to determine whether NADA and the prototypic arachidonoyl amino acid, N-arachidonoyl glycine (NAGly) modulate T-type ICa
Human recombinant T-type ICa (CaV3 channels) expressed in HEK 293 cells and native mouse T-type ICa were examined using standard whole-cell voltage clamp electrophysiology techniques.
N-arachidonoyl dopamine completely inhibited CaV3 channels with a rank order of potency (pEC50) of CaV3.3 (6.45) ≥ CaV3.1 (6.29) > CaV3.2 (5.95). NAGly (10 µmol·L−1) inhibited CaV3 ICa by approximately 50% or less. The effects of NADA and NAGly were voltage- but not use-dependent, and both compounds produced significant hyperpolarizing shifts in CaV3 channel steady-state inactivation relationships. By contrast with anandamide, NADA and NAGly had modest effects on CaV3 channel kinetics. Both NAGly and NADA inhibited native T-type ICa in mouse sensory neurons.
Conclusions and implications:
N-arachidonoyl dopamine and NAGly increase the steady-state inactivation of CaV3 channels, reducing the number of channels available to open during depolarization. These effects occur at NADA concentrations at or below to those affecting CB1 and TRPV1 receptors. Together with anandamide, the arachidonoyl neurotransmitter amides, NADA and NAGly, represent a new family of endogenous T-type ICa modulators.
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