ATPase Activity at the Functional Contacts between Retinal Cells which produce S-potential

Abstract

ACCORDING to Cajal¹, the horizontal cells of the teleost retina are arranged in three superimposed tangential layers formed by the external, medial and internal horizontal cells. Cajal classified the horizontal cells as short axon (Golgi II) cells and showed that radially oriented apical processes make contact with the receptor endings. Golgi studies and ultrastructural studies on the teleost retina (refs. 2 and 3 and unpublished results of V. Parthe and myself) confirm Cajal's description of these cells which in certain teleosts are enormous compared with the bipolar cells in the same retinal layer. Thin tangentially oriented extensions were not found in the external horizontal cells in Parthe's Golgi material. Such extensions of the medial and internal horizontal cells do not exceed in length the diameter of the cell body. Axon-like structures were not seen by Parthe or myself in any of the horizontal cell layers. In ultra-structural work⁴ each row of horizontal cells appears as a reticulum in which the cells are interconnected by membrane to membrane apposition of their lateral processes. Yamada and Ishikawa³ described in the carp, shark and ray retinae “fused membrane structures” at the apposition areas between the short lateral processes of the horizontal cells. But specialized junctions were not seen between horizontal cells belonging to different layers. These findings have been confirmed (Fig. 1) and similar fused membrane structures have been seen between stellate amacrine cells and between interstitial amacrine cells, in the regions where membrane to membrane contacts are formed between adjacent cells (my unpublished work). Light and electron microscopy shows that all the cells, which are of a giant size in certain teleost retinae, form tangential networks which are continuous throughout the retina (ref. 5 and unpublished results of V. Parthe and myself). Synaptic vesicles have not been observed in the region of the fused membrane structures (Fig. 1).