Patch-clamp Recording of Human Retinal Photoreceptors and Bipolar Cells


  • This paper is part of the Proceedings of the 12th International Conference on Retinal Proteins held at Awaji Island, Hyogo, Japan on 4–8 June 2006.

*email: (Mahito Ohkuma)


Photoreceptors and retinal bipolar cells are considered as nonspiking neurons; however, we recently showed that human rod photoreceptors can generate sodium action potentials in response to membrane depolarization from membrane potentials of −60 or −70 mV (Kawai et al., Neuron30 [2001] 451). We performed patch-clamp recording of human cone photoreceptors and retinal bipolar cells to examine whether functional voltage-gated sodium channels are expressed in these cells as well as rod photoreceptors. Under current-clamp conditions, the injection of depolarizing current steps into a cone photoreceptor-induced marked action potentials. These action potentials were blocked by 1 µM tetrodotoxin, a voltage-gated sodium channel blocker. Under voltage-clamp conditions, depolarizing voltage steps-induced a fast transient inward current in several bipolar cells (n = 4/78). This current was activated from −70 to +20 mV (maximal at −10 mV) and inactivated within 5 ms. The 10–90% rise time of this current was shorter than another inward current (less than one-hundredth). These results indicate that human cones and bipolar cells express voltage-gated sodium channels as rod photoreceptors. Sodium channels may serve to amplify the release of a neurotransmitter and to accelerate the light–dark change in photosignals.