EFFECTS OF PHOSPHODIESTERASE INHIBITORS AND FORSKOLIN ON CYCLIC GMP-ACTIVATED CHANNELS IN INTACT ISOLATED CELLS OF THE CHICK PINEAL-GLAND

Application of the phosphodiesterase inhibitors isobutylmethylxanthine (100 mu M) caused activation of low-conductance cationic channels in intact acutely-isolated chick pineal cells. This effect required conti nued contact between the cytoplasmic face of the patch membrane and th e cytoplasm. The biophysical properties of the channels were identical to those of cyclic GMP-activated channels described previously in exc ised patches. Application of 40 mu M forskolin did not cause activatio n of the low-conductance channels. A second population of spontaneousl y active large-conductance cationic channels was observed in some patc hes. Gating of large-conductance channels was not affected by phosphod iesterase inhibitors of forskolin. These results support the theory th at phototransduction cascades similar to those of the vertebrate retin a are also present in chick pineal cells.