Modulation of Recombinant Human T-type calcium Channels by Δ9-tetrahydrocannabinolic acid in vitro

Introduction Low voltage-activated T-type calcium channels (T-type I Ca ), Ca V 3.1, Ca V 3.2, and Ca V 3.3 are opened by small depolarizations from the resting membrane potential in many cells and have been associated with neurological disorders including absence epilepsy and pain. Δ 9 -tetrahydrocannabinol (THC) is the principal psychoactive compound in Cannabis and also directly modulates T-type I Ca , however, there is no information about functional activity of most phytocannabinoids on T-type calcium channels, including Δ 9 -tetrahydrocannabinol acid (THCA), the natural non-psychoactive precursor of THC. The aim of this work was to characterize THCA effects on T-type calcium channels. Materials and Methods We used HEK293 Flp-In-TREx cells stably expressing Ca V 3.1, 3.2 or 3.3. Whole-cell patch clamp recordings were made to investigate cannabinoid modulation of I Ca . Results THCA and THC inhibited the peak current amplitude Ca V 3.1 with a p EC 50 s of 6.0 ± 0.7 and 5.6 ± 0.4, respectively. 1μM THCA or THC produced a significant negative shift in half activation and inactivation of Ca V 3.1 and both drugs prolonged Ca V 3.1 deactivation kinetics. THCA (10 μM) inhibited Ca V 3.2 by 53% ± 4 and both THCA and THC produced a substantial negative shift in the voltage for half inactivation and modest negative shift in half activation of Ca V 3.2. THC prolonged the deactivation time of Ca V 3.2 while THCA did not. THCA inhibited the peak current of Ca V 3.3 by 43% ± 2 (10μM) but did not notably affect Ca V 3.3 channel activation or inactivation, however, THC caused significant hyperpolarizing shift in Ca V 3.3 steady state inactivation. Discussion THCA modulated T-type I Ca currents in vitro , with significant modulation of kinetics and voltage dependence at low μM concentrations. This study suggests that THCA may have potential for therapeutic use in pain and epilepsy via T-type channel modulation without the unwanted psychoactive effects associated with THC.