(Endo)cannabinoid signaling in human bronchial epithelial and smooth muscle cells

We investigated the pathways used by various (endo)cannabinoids in regulating intracellular calcium homeostasis, adenylyl cyclase and ERK signaling, in bronchial epithelial cells as well as smooth muscle cells. In DDT1 MF2 smooth muscle cells the synthetic cannabinoid CP55,940 increases [Ca2+]i by a CB1-receptor-dependent signaling pathway which is mediated by arachidonic acid. In 16HBE14o- bronchial epithelial cells, the cannabinoids Δ9-THC, CP55,940 and (low concentrations of) virodhamine increase [Ca2+]i, via mobilization from internal stores and subsequent capacitive calcium entry (CCE). Higher concentrations of virodhamine increase [Ca2+]i in these epithelial cells via a non-CB1-receptor, non-CB2-receptor dependent NCCE, presumably involving TRPV1, TRPV4 and TRPC6 channels. In these epithelial cells CB1- and CB2-receptors differentially modulate adenylyl cyclase. Virodhamine and CP55,940 predominantly inhibit cAMP accumulation, which is mediated by CB2-receptors, coupled to Gi/o-proteins. After pertussis toxin treatment a Gs-mediated activation of adenylyl cyclase was unmasked, enhancing cAMP accumulation. Activation of the dominant inhibitory CB2-receptor signaling pathway diminished cAMP accumulation and TNFα-induced interleukin-8 (IL-8) release at similar cannabinoid concentrations. Cell survival of bronchial epithelial cells is attenuated by virodhamine, independent of CB1- and CB2-receptor mediated changes in cAMP levels and [Ca2+]i. CB1- and CB2-receptors reciprocally modulate virodhamine-induced attenuation of cell survival; these effects converge on the level of ERK1/2 activation.