Dopamine, acting via cyclic adenosine 3':5'-monophosphate (cAMP), has been shown to enhance a kainate-gated ionic conductance in white perch retinal horizontal cells in vitro. To determine whether this effect involves stimulation of a protein kinase, kainate-gated currents were observed in cultured horizontal cells that were dialyzed with the catalytic subunit of cAMP-dependent protein kinase. Intracellular application of catalytic subunit or cAMP, but not heat-inactivated catalytic subunit, caused significant enhancement of the kainate-evoked currents. These results suggest that kainate-gated channels in horizontal cells may be modified by a phosphorylation event.