THE MOLECULAR MECHANISM OF VISUAL EXCITATION AND ITS RELATION TO THE STRUCTURE AND COMPOSITION OF THE ROD OUTER SEGMENT

Abstract

The idea that mediates is a conceptual thread that has woven through biological research for decades. The molecules in biological superstructures such as membranes are vectorially oriented in both space and time. As with the code provided by the Rosetta Stone, if we could learn to recognize the meaning of the vectorial arrows and follow them through their causally interconnected junctions, we would indeed understand how function is mediated through the dynamic structure of the component molecules. Few processes have as many structural signposts suggesting causal interpretation as does vertebrate vision. Rod and cone outer segments are so structurally specialized for the translation of optical into ionic events that even their enormous concentration of mitochondria (that are essential for driving the large light-modulated current in photoreceptors) are relocated in an adjacent chamber. The rod disk and cytoplasmic transduction apparatus of the receptor outer segment is axially repeated a thousand times with great precision. At the level of a single axial unit, which consists of a disk membrane