Abstract
Abstract: :
Purpose: Hyperpolarization–activated and cyclic nucleotide–gated (HCN) channels play an important role in the generation of rhythmic activity and in the shaping of cellular responses. The purpose was to reveal the expression of HCN channels in the mouse retina. Methods: Antibodies specific for the four isoforms HCN1 – HCN4 were used for immunocytochemical detection of HCN channels in the adult and developing mouse retina. HCN currents were recorded in identified cells in mouse retinal slices with the patch clamp technique. Results: All four HCN channel isoforms are expressed in the adult mouse retina. HCN1–immunoreactivity is strongest in rods, cones, and type 5 cone bipolar cells. HCN1 is localized in a punctiform fashion at the axon terminals of rod bipolar cells. HCN2–immunoreactivity is found throughout the inner plexiform layer, but is strongest in a subpopulation of large putative OFF–ganglion cells. HCN3–positive processes are ramifying in the OFF–sublamina of the IPL. HCN4 is strongly expressed in type 3 cone bipolar cells. All HCN isoforms are expressed in some amacrine and ganglion cells. In photoreceptors HCN1–immunoreactivity is observed at birth and increases in intensity during postnatal development. In the inner retina expression of all four HCN channel isoforms starts at postnatal days 6 – 8. The analysis of HCN currents recorded in photoreceptors and bipolar cells agrees well with the immunohistochemical expression pattern. Conclusions: HCN channels are differentially expressed in various cell types of the retina and may be involved in retinal signal processing at different levels.
Keywords: retina: proximal (bipolar, amacrine, and ganglion cells) • bipolar cells • ion channels