Figure 2.

Concentration-dependent regulation of HCN1 current by THC and CBD. (A) Steady-state current values from a representative cell following repetitive pulses to −130 mV from V_H = 0 mV with the addition of 0, 10, 20, 30, and 50 μM CBD. (B) Concentration dependence of HCN1 activation by CBD (■) at −130 mV (n = 13). This activation of HCN1 persists in the presence of the CB1R antagonist 10 μM AM-251 (°) (n = 5). A total of 50% Max response (EC₅₀) for CBD is elicited at 28.5 μM, with a 91% maximal increase in current. (C) CBD has no effects on uninjected oocytes, indicating that we are not observing effects on background currents. (D) CBD activated currents can be fully inhibited by 500 μM ZD7288. This indicates that CBD is only activating HCN1 currents, and not activating a background current in oocytes. (E) Steady-state currents from a representative cell following repetitive pulses to −130 mV in 0, 10, 25, and 50 μM THC. (F) Steady-state currents from a representative cell following repetitive pulses to −130 mV in the presence of the quantity of methanol used as a vehicle for 0, 10, 25, and 50 μM CBD/THC. (G) Concentration dependence of HCN1 inhibition by THC (■) or methanol (□) at −130 mV (n = 5). THC induces a 63% maximal block of HCN1 currents, with a half-maximal response (Relative IC₅₀) of 21.8 μM. 50% block of total current (Absolute IC₅₀) occurs at 28.9 μM. Methanol induces < a 5% decrease in current at concentrations above 20 μM (n = 4).