| Popis: |
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)-tetrahydrocannabinolic acid (THCA), the natural nonpsychoactive 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 pEC(50)s of 6.0±0.7 and 5.6±0.4, respectively. THC (1 μM) 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% (10 μM) 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 through T-type calcium channel modulation without the unwanted psychoactive effects associated with THC. |
