Inhibition of human recombinant T‐type calcium channels by phytocannabinoids in vitro

Abstract

Background and Purpose T‐type Ca channels ( I Ca ) regulate neuronal excitability and contribute to neurotransmitter release. The phytocannabinoids Δ 9 ‐tetrahydrocannabinol and cannabidiol effectively modulate T‐type I Ca , but effects of other biologically active phytocannabinoids on these channels are unknown. We thus investigated the modulation of T‐type I Ca by low abundance phytocannabinoids. Experimental Approach A fluorometric (fluorescence imaging plate reader [FLIPR]) assay was used to investigate modulation of human T‐type I Ca (Ca V 3.1, 3.2 and 3.3) stably expressed in FlpIn‐TREx HEK293 cells. The biophysical effects of some compounds were examined using whole‐cell patch clamp recordings. Key Results In the FLIPR assay, all 11 phytocannabinoids tested modulated T‐type I Ca , with most inhibiting Ca V 3.1 and Ca V 3.2 more effectively than Ca V 3.3. Cannabigerolic acid was the most potent inhibitor of Ca V 3.1 ( p IC 50 6.1 ± 0.6) and Ca V 3.2 ( p IC 50 6.4 ± 0.4); in all cases, phytocannabinoid acids were more potent than their corresponding neutral forms. In patch clamp recordings, cannabigerolic acid inhibited Ca V 3.1 and 3.2 with similar potency to the FLIPR assay; the inhibition was associated with significant hyperpolarizing shift in activation and steady‐state inactivation of these channels. In contrast, cannabidiol, cannabidivarin, and cannabigerol only affected channel inactivation. Conclusion and Implications Modulation of T‐type calcium channels is a common property of phytocannabinoids, which all increase steady‐state inactivation at physiological membrane potentials, with some also affecting channel activation. Thus, T‐type I Ca may be a common site of action for phytocannabinoids, and the diverse actions of phytocannabinoids on channel gating may provide insight into structural requirement for selective T‐type I Ca modulators.

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