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Neurosci Res. 2006 Feb;54(2):85-94. Epub 2005 Nov 17.

Kinetic evaluation of photosensitivity in genetically engineered neurons expressing green algae light-gated channels.

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1
Department of Developmental Biology and Neuroscience, Tohoku University Graduate School of Life Sciences, 2-1 Seiryo-machi, Sendai 980-8575, Japan.

Abstract

Neurons become photosensitive by genetically introducing one of green algae-derived protein, channelrhodopsin-2 (ChR2). Here, we quantitatively investigated the rapidness of the light-gated current of ChR2 expressed in PC12 cells using blue light-emitting diode (LED) light. The light-gated current consists of two components, inactivating and non-inactivating. The magnitude of inactivating component was almost linearly related to the light intensity. The non-inactivating component showed a tendency to saturate at high illumination. Both the activation and inactivation rates of the light-gated current were linearly dependent on the light intensity. However, the activation rate (turning-on rate) is about 10-fold faster than the inactivation rate. Although the turning-off time constant was little dependent on the light intensity, that at the end of 1s light pulse was about two-fold larger than that at 20 ms. Neurons are also made photosensitive by the expression of ChR2 in the living animal. Since both the turning-on and turning-off time constants of light-gated current was smaller than the membrane time constant of neurons, the LED light illumination of the photosensitive neurons was enough to evoke action potentials in a pulse-to-pulse manner in an acute slice of hippocampus.

PMID:
16298005
DOI:
10.1016/j.neures.2005.10.009
[Indexed for MEDLINE]
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