Cannabinoid receptor agonists inhibit depolarization-induced calcium influx in cerebellar granule neurons

Abstract

Neuronal cannabinoid receptors (CB1) are coupled to inhibition of voltage-sensitive Ca2+ channels (VSCCs) in several cell types. The purpose of these studies was to characterize the interaction between endogenous CB1 receptors and VSCCs in cerebellar granule neurons (CGN). Ca2+ transients were evoked by KCl-induced depolarization and imaged using fura-2. The CB1 receptor agonists CP55940, Win 55212-2 and N-arachidonylethanolamine (anandamide) produced concentration-related decreases in peak amplitude of the Ca2+ response and total Ca2+ influx. Pre-treatment of CGN with pertussis toxin abolished agonist-mediated inhibition. The inhibitory effect of Win 55212-2 on Ca2+ influx was additive with inhibition produced by ω-agatoxin IVA and nifedipine but not with ω-conotoxin GVIA, indicating that N-type VSCCs are the primary effector. Paradoxically, the CB1 receptor antagonist, SR141716, also inhibited KCl-induced Ca2+ influx into CGN in a concentration-related manner. SR141716 inhibition was pertussis toxin-insensitive and was not additive with the inhibition produced by Win 55212-2. Confocal imaging of CGN in primary culture demonstrate a high density of CB1 receptor expression on CGN plasma membranes, including the neuritic processes. These data demonstrate that the CB1 receptor is highly expressed by CGN and agonists serve as potent and efficacious inhibitory modulators of Ca2+ influx through N-type VSCC.