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F. Muller, J. Berthold, E. Ivanova, B. Kaupp; Differential Expression of HCN Channels in the Retinae of Rat and Mouse . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4144.
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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. In previous studies, currents carried by HCN channels were termed If, Ih, or Iq. Four genes encoding HCN channels (HCN1-4) have been cloned from mammals. The purpose of this study is to compare the expression of HCN channels in the retinae of rat and mouse. Methods: We localized HCN channels using immunohistochemistry with subtype specific antibodies. Results: All four HCN channel isoforms are expressed in the rat and in the mouse retina. In general, HCN channel distribution is rather similar in the retinae of the two species. Rods and cones express HCN1 in the inner segment, soma and axon. HCN3 was found at cone pedicles. HCN4 was strongly expressed in type 3 bipolar cells. We found both HCN1 and HCN4 in type 5 and type 6 bipolar cells. In rat retina, HCN2 is highly localized to the axon terminal systems of rod bipolar cells (and type 7, 8, and 9 bipolar cells). In contrast, in mouse retina, HCN1 instead of HCN2 was found at the axon terminal of rod bipolar cells. HCN1, HCN2 and HCN4 are also expressed in some amacrine cells and ganglion cells. Conclusions: In summary, HCN channels are differentially expressed in various cell types of the retina and may be involved in retinal signal processing at different levels. The HCN channel expression patterns provide the basis for studies on HCN channel function in the retinal network using the patch-clamp technique and channel knock-out strategies.
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