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

Neuronal cannabinoid receptors (CB1) are coupled to inhibition of voltage-s ensitive Ca2+ channels (VSCCs) in several cell types. The purpose of these studies was to characterize the interaction between endogenous CB1 receptor s and VSCCs in cerebellar granule neurons (CGN). Ca2+ transients were evoke d by KCI-induced depolarization and imaged using fura-2. The CB1 receptor a gonists CP55940, Win 55212-2 and N-arachidonylethanolamine (anandamide) pro duced concentration-related decreases in peak amplitude of the Ca2+ respons e and total Ca2+ influx. Pre-treatment of CGN with pertussis toxin abolishe d agonist-mediated inhibition. The inhibitory effect of Win 55212-2 on Ca2 influx was additive with inhibition produced by omega -agatoxin IVA and ni fedipine but not with omega -conotoxin GVIA, indicating that N-type VSCCs a re the primary effector. Paradoxically, the CB1 receptor antagonist, SR1417 16, also inhibited KCI-induced Ca2+ influx into CGN in a concentration-rela ted 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 expressio n on CGN plasma membranes, including the neuritic processes. These data dem onstrate that the CB1 receptor is highly expressed by CGN and agonists serv e as potent and efficacious inhibitory modulators of Ca2+ influx through N- type VSCC.