Inhibitory effect of adenosine on transmission in sympathetic ganglia

The effect of bath-applied adenosine on transmission in the isolated superior cervical ganglion of the rat was investigated. The compound post ganglionic action potential was recorded as an index of ganglionic transmission. Adenosine and 2-chloroadenosine were equipotent in producing a dose-dependent inhibition of the amplitude of the compound action potential. At the highest concentration tested (1 mM) adenosine and 2-chloroadenosine produced about 30% decrease in the amplitude of the compound action potential. This inhibitory effect was antagonized by theophylline (1 and 100 microM) which by itself had no significant effect on ganglionic transmission. The adenosine uptake blocker dipyridamole (1 and 100 microM) failed to potentiate the inhibitory action of adenosine. Both 4-aminopyridine (20 microM) and high frequencies of stimulation (3, 10 and 20 Hz) were effective in nearly completely abolishing the inhibitory effect of adenosine on ganglionic transmission. The results suggest that the inhibitory effect of adenosine on ganglionic transmission may be the result of activation of presynaptic adenosine receptors in the ganglion.