The stimulatory effect of cannabinoids on calcium uptake is mediated by G_s GTP-binding proteins and cAMP formation

Cannabinoids are neurodepressive drugs that convey their cellular action through G_i/o GTP-binding proteins which reduce cAMP formation and Ca²⁺ influx. However, a growing body of evidence indicates that the stimulatory effects of cannabinoids include the elevation in cAMP and cytosolic Ca²⁺ concentration. The present study expands our previous findings and demonstrates that, in N18TG2 neuroblastoma cells, the cannabinoid agonist desacetyllevonantradol (DALN) stimulates both cAMP formation and Ca ²⁺ uptake. The stimulatory effect of DALN on cAMP formation was not eliminated by blocking Ca²⁺ entry to the cells, while its stimulatory effect on Ca²⁺ uptake was abolished by blocking cAMP-dependent protein kinase. Furthermore, elevating cAMP by forskolin stimulated calcium uptake, while elevating the intracellular Ca²⁺ concentration by ionomycin or KCl failed to stimulate cAMP formation. These findings suggest that cAMP production precedes the influx of Ca²⁺ in the cannabinoid stimulatory cascade. The stimulatory effect of DALN on calcium uptake resisted pertussis toxin treatment, and was completely blocked by introducing anti-G_s antibodies into the cells, indicating that the stimulatory activity of cannabinoids is mediated by G_s GTP-binding proteins. The relevance of the cellular stimulatory activity of DALN to the pharmacological profile of cannabinoid drugs is discussed.