Intracellular recordings were made from S neurons of the submucosal plexus isolated from the guinea pig ileum. Adenosine or its analog 2-chloroadenosine (CADO) depolarized about 80% of neurons; previous work has shown that this results from activation of an A2 receptor. The depolarization was associated with an increase in membrane input resistance, became smaller with membrane hyperpolarization, reversed polarity at the potassium equilibrium potential and was mimicked and occluded by calcium-free solutions or by cadmium, suggesting that it is due to a reduction in a calcium-dependent potassium conductance. Both forskolin (though not 1,9-dideoxyforskolin) and phorbol 12,13-dibutyrate (PDBu) mimicked and occluded the action of CADO. Staurosporine (a nonspecific inhibitor of protein kinases) blocked the depolarization induced by the phorbol ester within 5 min, and blocked the effects of forskolin and CADO in 15-35 min. The depolarization caused by CADO was inhibited by the specific inhibitor of protein kinase A KT5720 [(8R*,9S*,11S*)-(-)-9-hydroxy-9-n-hexylester-8-methyl-2,3,9,10-tet rahydro-8,11-epoxy-1H,8H,11H-2,7b,11a-triazadibenzo[a,g]c ycloocta[cd e]-trin-den-1-one], whereas this inhibitor did not affect the depolarization induced by PDBu. The results are consistent with the control of this potassium conductance by protein kinase C, protein kinase A and intracellular calcium, and they indicate that adenosine reduces the conductance by activating protein kinase A.