Cyclic nucleotides injected intracellularly into rat superior cervical ganglion cells.

Intracellular iontophoresis of either adenosine 3',5'-monophosphate or guanosine 3',5'-monophosphate produces a membrane depolarization and an increased membrane conductance in sympathetic ganglion cells of the rat superior cervical ganglion. Since adenosine 3',5'-monophosphate did not cause a membrane hyperpolarization, it is difficult to assign it a second messenger role in the mediation of the slow inhibitory postsynaptic potential. However, these results do not rule out the possibility that the cyclic nucleotides, at the intracellular concentrations attained in these experiments, participate in cellular processes that contribute to conductance changes which result in depolarization of the ganglion cell membrane.