Was wissen wir über den molekularen Mechanismus der Erregung von Lichtsinneszellen?

The mechanism of transduction of the light stimulus into an electrical response signal is described for visual cells of vertebrates and invertebrates. Absorption of a photon by a rhodopsin molecule in the photosensory membrane of the visual cell leads to a delayed, relatively large single-photon-evoked response, the elementary excitatory response. The rhodopsin molecule starts an enzyme cascade via a G-protein. This leads to a considerably amplified decrease (vertebrates), or increase (invertebrates) of a large number of intracellular messenger molecules. Binding of these messenger molecules causes the opening of the sodium-preferring ion channels in the plasma membrane. Our present knowledge of the molecular mechanisms involved is described.