Light-induced fluctuations in membrane current of single toad rod outer segments

Abstract

VERTEBRATE photoreceptors respond to illumination with a reduction in the steady current of Na ions which in darkness flows inwards across the outer segment membrane; this results in hyperpolarisation of the cells1. The light responses of the receptors can be studied by measuring extracellular voltage gradients2 or by intracellular recording1, but these methods can only provide information averaged over many photoreceptors owing respectively to high extracellular conductivity and to the presence of electrical coupling between cells3-6. This averaging and the presence of dark voltage noise in photoreceptors6,7 have prevented observation of the electrical effects of individual photoisomerisations. To try to record these elementary events and to localise the source of the dark noise, we have developed a method for recording the membrane current of a single rod outer segment. The technique is based on that used by Neher and Sakmann 8 on muscle fibres. Show more