Intracellular calcium signals mediated by the activation of voltage-gated calcium channels (VGCC) play a key role in cellular function in health and disease. There is ample evidence that VGCC can be modulation via G-protein coupled receptors. One of these receptors is the cannabinoid receptor CB1, while CB2 receptor poorly modulates VGCCs. In this study we have analyzed the effect of the highly specific CB2 receptor agonist JWH-133 (K_D = 3.4 nM) on VGCC in sensory neurons from wt and CB receptor knockout mice. The agonist is currently used in many studies to analyze CB2 receptor mediated signalling in various tissues. In mouse dorsal root ganglion (DRG) neurons, JWH-133 inhibited high threshold activated (HVA) calcium currents in a concentration-dependent manner. A typical experiment is shown on the left where 200 nM inhibited ~50% of the barium currents through calcium channels. Maximum block developed within 1 sec and block was fully reversible upon washout. Calcium channel block was on L, N, P/Q and R-type. Low threshold activated (LVA) calcium currents were not significantly affected by JWH-133 up to 10 mM. Similar results were obtained when G-proteins were maximally activated by intracellular application of GTP-g-S (1 mM). The effect of JWH-133 was also observed on barium currents through calcium channels from mice lacking CB receptors. Our findings strongly suggest that JWH-133 besides its actions on CB2 receptors directly and selectively affects neuronal HVA calcium channels. Therefore one should be cautious when using this agent to analyse specific effects on CB2 receptors in nanomolar concentrations.

Figure 1