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 microM) caused activation of a low-conductance cationic channels in intact acute-isolated chick pineal cells. This effect required continued contact between the cytoplasmic face of the patch membrane and the cytoplasm. The biophysical properties of the channels were identical to those of cyclic GMP-activated channels described previously on excised patches. Application of 40 microM forskolin did not cause activation of the low-conductance channels. A second population of spontaneously active large-conductance cationic channels was observed in some patches. Gating of large-conductance channels was not affected by phosphodiesterase inhibitors of forskolin. These results support the theory that phototransduction cascades similar to those of the vertebrate retina are also present in chick pineal cells.