2003 Fiscal Year Final Research Report Summary
Physiological analyses of voltage-gated ion channels and their molecular identifications in sensory neurons.
| Project/Area Number |
14580779
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Neuroscience in general
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| Research Institution | Fujita Health University |
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Principal Investigator |
MIYACHI Ei-ichi Fujita Health University, School of Medicine, Professor, 医学部, 教授 (90129685)
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| Co-Investigator(Kenkyū-buntansha) |
HORIGUCHI Masayuki Fujita Health University, School of Medicine, Professor, 医学部, 教授 (70209295)
OHKUMA Ahito Fujita Health University, School of Medicine, Research Associate, 医学部, 助手 (50329710)
KAWAI Fusao Fujita Health University, School of Medicine, Associate professor, 医学部, 助教授 (20300725)
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| Project Period (FY) |
2002 – 2003
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| Keywords | sensory organ / retina / photoreceptor / retinal bipolar cell / olfactory cell / voltage-gated sodium channel / voltage-gated calcium channel / h channel |
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| Research Abstract |
All vertebrate photoreceptors, including those of humans, respond to light stimuli with a graded hyperpolarization, and are commonly thought to be non-spiking neurons. To examine whether human photoreceptors can elicit action potentials, we studied surgically excised human retina using the whole-cell patch-clamp recording technique. A small piece (diameter less than 1 mm) of retina was excised from patients with retinal detachment during the surgical procedure to re-attach the retina. All experiments were performed in compliance with the guideline of the Declaration of Helsinki and approved by the ethics committee of our institute. We found that photoreceptors express voltage-gated Na^+ channels, and generate Na^+ action potentials in response to membrane de polarization. This suggests that Na spikes might be elicited at the termination of a bright light stimulus. The Na action potentials would serve to amplify the release of neurotransmitter at the sudden offset of a bright light, and thus selectively amplify the "OFF" part of the light signal.
We also examined whether human rod photoreceptors express hyperpolarization-activated cationic currents (Ih). The slow inward current induced by hyperpolarization was markedly reduced by bath application of 3 mM Cs^+, a blocker of Ih,. Bath application of 3 mM Cs^+ also blocked the steady inward current. Our findings suggest that Ih becomes activated during large hyperpolarizations generated by bright illumination and may modify the waveform of the photovoltage.
The sense of vision in humans is quite robust and visual flickering is rarely experienced. Under current-clamp conditions, blockage by Cs^+, Tl^+ and ZD7288 of an h current hyperpolarized the resting potentials of cones and rods by 〜10-15 mV, and surprisingly generated spontaneous action potentials. We suggest that the h current may contribute to preventing visual flickering by inhibiting the generation of spontaneous Na^+ spikes in human cones and rods.
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