Patch-clamp recording of human retinal photoreceptors and bipolar cells.
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., Neuron 30 [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 microM 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.
Ohkuma
Mahito
M
Department of Physiology, School of Medicine, Fujita Health University, Toyoake, Aichi, Japan. m-ohkuma@fujita-hu.ac.jp
Kawai
Fusao
F
Horiguchi
Masayuki
M
Miyachi
Ei-Ichi
E
D000328:Adult; D006801:Humans; D066298:In Vitro Techniques; D015640:Ion Channel Gating; D008564:Membrane Potentials; D018408:Patch-Clamp Techniques; D018462:Photobiology; D051245:Retinal Bipolar Cells / Q000378:metabolism* / Q000528:radiation effects; D017949:Retinal Cone Photoreceptor Cells / Q000166:cytology / Q000378:metabolism* / Q000528:radiation effects; D015398:Signal Transduction; D015222:Sodium Channels / Q000378:metabolism
D015222:Sodium Channels