Fig. 5.
The cannabinoid receptor inverse agonist SR 141716A blocks the effect of norepinephrine on the Ca2+ current. A, Application of 10 μm norepinephrine (NE, open bar) inhibited the Ca2+ current in an uninjected SCG neuron. A subsequent application of 1 μm SR 141716A (SR, filled bar) had no effect on the Ca2+current. A second application of norepinephrine again inhibited the Ca2+ current. Right, Superimposed current traces in the absence (Control) and in the presence of norepinephrine (NE), SR 141716A (SR), and again in the presence of norepinephrine (NE after SR). B, In an SCG neuron microinjected with 50 ng/μl hCB1 cDNA, norepinephrine (NE, open bar) reversibly decreased the Ca2+current. A subsequent application of 1 μm SR 141716A (SR, filled bar) increased both the control (open circle) and facilitated (filled circle) Ca2+ current. The Ca2+ current remained enhanced after superfusion with external solution. A subsequent application of norepinephrine now failed to inhibit the Ca2+ current. Right, Superimposed current traces in the absence (Control) and presence of the first application of norepinephrine (NE), SR 141716A (SR), and the second application of norepinephrine (NE after SR).C, Summary of the changes in the control Ca2+ current amplitude in uninjected SCG neurons (filled bars) and in neurons microinjected with 50 ng/μl hCB1 cDNA (open bars). The effect of norepinephrine (NE, open bar) was abolished (**p < 0.001) after the application of SR 141716A (NE after SR, open bar). SR 141716A significantly increased (**p < 0.001) the Ca2+ current in neurons microinjected with 50 ng/μl hCB1 cDNA (SR, open bar) compared to uninjected SCG neurons (SR, filled bar). SR 141716A (NE after SR, filled bar) had no effect on the Ca2+ current inhibition by norepinephrine (NE, filled bar) in uninjected neurons. Number of neurons tested is indicated. D, SR 141716A increased the control Ca2+ current to a greater extent in SCG neurons microinjected with 100 ng/μl hCB1 cDNA than in neurons microinjected with 50 ng/μl hCB1 cDNA. The number of neurons tested is indicated.