Thermal activation of the visual transduction mechanism in retinal rods [16]

INVERTEBRATE photoreceptors show electrical changes which apparently result from isomerisation of single rhodopsin molecules by light or thermal energy^1-3. Observation of corresponding phenomena in vertebrates has been prevented by intercellular electrical coupling, which averages membrane potential over many photoreceptors^4-6. Recently, however, recordings of membrane current from individual rod outer segments have revealed responses to single photons^7,8. Here we report that similar electrical events occasionally occur in darkness, perhaps because of thermal isomerisation of rhodopsin.