Limits...
Strategies for expanding the operational range of channelrhodopsin in optogenetic vision.

Mutter M, Münch TA - PLoS ONE (2013)

Bottom Line: Currently existing variants of channelrhodopsin--engineered for use in neurophysiological research--do not necessarily support the goal of vision restoration optimally, due to two factors: First, the nature of the light stimulus is fundamentally different in "optogenetic vision" compared to "optogenetic neuroscience".In this study, by using a computational model, we investigate properties of channelrhodopsin that might improve successful vision restoration.Furthermore, the computational model used for this study is provided as an interactive tool for the research community.

View Article: PubMed Central - PubMed

Affiliation: Centre for Integrative Neuroscience & Bernstein Center for Computational Biology, University Tübingen, Tübingen, Germany.

ABSTRACT
Some hereditary diseases, such as retinitis pigmentosa, lead to blindness due to the death of photoreceptors, though the rest of the visual system might be only slightly affected. Optogenetics is a promising tool for restoring vision after retinal degeneration. In optogenetics, light-sensitive ion channels ("channelrhodopsins") are expressed in neurons so that the neurons can be activated by light. Currently existing variants of channelrhodopsin--engineered for use in neurophysiological research--do not necessarily support the goal of vision restoration optimally, due to two factors: First, the nature of the light stimulus is fundamentally different in "optogenetic vision" compared to "optogenetic neuroscience". Second, the retinal target neurons have specific properties that need to be accounted for, e.g. most retinal neurons are non-spiking. In this study, by using a computational model, we investigate properties of channelrhodopsin that might improve successful vision restoration. We pay particular attention to the operational brightness range and suggest strategies that would allow optogenetic vision over a wider intensity range than currently possible, spanning the brightest 5 orders of naturally occurring luminance. We also discuss the biophysical limitations of channelrhodopsin, and of the expressing cells, that prevent further expansion of this operational range, and we suggest design strategies for optogenetic tools which might help overcoming these limitations. Furthermore, the computational model used for this study is provided as an interactive tool for the research community.

Show MeSH

Related in: MedlinePlus

Membrane potential of cells expressing different ChR variants.The light stimulus (top) was identical to Fig. 5. The current traces from Fig. 5 are translated into membrane voltage according to the membrane equation −C V’(t) = (V(t) − Vrest)/R+kexpgChR (V(t) − Vreverse) with C = 6 pF, R = 5 GOhm, Vrest = −55 mV, Vreverse = 0 mV, and gChR = (g1O1+g2O2). A: Membrane potential fluctuations caused by currents carried by Variant A (Fig. 5B) and Variant B (Fig. 5C). B: Effect of different expression levels kexp on membrane potential modulation. C: Expressing Variant A and Variant B together in a single cell, at moderate expression levels, leads to modulation of membrane potential over 7 orders of magnitude. In each panel, we show the hypothetical saturation level of the cell (−25 mV). Depolarization beyond this level is indicated by dimly printed voltage traces.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3842264&req=5

pone-0081278-g006: Membrane potential of cells expressing different ChR variants.The light stimulus (top) was identical to Fig. 5. The current traces from Fig. 5 are translated into membrane voltage according to the membrane equation −C V’(t) = (V(t) − Vrest)/R+kexpgChR (V(t) − Vreverse) with C = 6 pF, R = 5 GOhm, Vrest = −55 mV, Vreverse = 0 mV, and gChR = (g1O1+g2O2). A: Membrane potential fluctuations caused by currents carried by Variant A (Fig. 5B) and Variant B (Fig. 5C). B: Effect of different expression levels kexp on membrane potential modulation. C: Expressing Variant A and Variant B together in a single cell, at moderate expression levels, leads to modulation of membrane potential over 7 orders of magnitude. In each panel, we show the hypothetical saturation level of the cell (−25 mV). Depolarization beyond this level is indicated by dimly printed voltage traces.

Mentions: Fig. 6A shows the modulation of the membrane potential of cell expressing either Variant A or Variant B, using the same stimulus as in Fig. 5. Given the high input resistance of the cell, the weak current elicited by Variant A in section −3 of the stimulus (Fig. 5B) already has a sizable effect on membrane voltage (Fig. 6A), and depolarization in section −1 can already reach and exceed our voltage ceiling of −25 mV. Due to the properties of Variant A, the membrane potential decreases in stimulus sections 1 and 2 and almost reaches the resting potential again in section 3. In contrast to Variant A, the membrane depolarization of Variant B is a monotonic function of brightness. In stimulus section 1, the cell is already fully saturated (i.e. depolarized beyond −25 mV). Note that by design, wild-type ChR would behave the same as Variant B, shifted 2 log units to darker intensity values.


Strategies for expanding the operational range of channelrhodopsin in optogenetic vision.

Mutter M, Münch TA - PLoS ONE (2013)

Membrane potential of cells expressing different ChR variants.The light stimulus (top) was identical to Fig. 5. The current traces from Fig. 5 are translated into membrane voltage according to the membrane equation −C V’(t) = (V(t) − Vrest)/R+kexpgChR (V(t) − Vreverse) with C = 6 pF, R = 5 GOhm, Vrest = −55 mV, Vreverse = 0 mV, and gChR = (g1O1+g2O2). A: Membrane potential fluctuations caused by currents carried by Variant A (Fig. 5B) and Variant B (Fig. 5C). B: Effect of different expression levels kexp on membrane potential modulation. C: Expressing Variant A and Variant B together in a single cell, at moderate expression levels, leads to modulation of membrane potential over 7 orders of magnitude. In each panel, we show the hypothetical saturation level of the cell (−25 mV). Depolarization beyond this level is indicated by dimly printed voltage traces.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3842264&req=5

pone-0081278-g006: Membrane potential of cells expressing different ChR variants.The light stimulus (top) was identical to Fig. 5. The current traces from Fig. 5 are translated into membrane voltage according to the membrane equation −C V’(t) = (V(t) − Vrest)/R+kexpgChR (V(t) − Vreverse) with C = 6 pF, R = 5 GOhm, Vrest = −55 mV, Vreverse = 0 mV, and gChR = (g1O1+g2O2). A: Membrane potential fluctuations caused by currents carried by Variant A (Fig. 5B) and Variant B (Fig. 5C). B: Effect of different expression levels kexp on membrane potential modulation. C: Expressing Variant A and Variant B together in a single cell, at moderate expression levels, leads to modulation of membrane potential over 7 orders of magnitude. In each panel, we show the hypothetical saturation level of the cell (−25 mV). Depolarization beyond this level is indicated by dimly printed voltage traces.
Mentions: Fig. 6A shows the modulation of the membrane potential of cell expressing either Variant A or Variant B, using the same stimulus as in Fig. 5. Given the high input resistance of the cell, the weak current elicited by Variant A in section −3 of the stimulus (Fig. 5B) already has a sizable effect on membrane voltage (Fig. 6A), and depolarization in section −1 can already reach and exceed our voltage ceiling of −25 mV. Due to the properties of Variant A, the membrane potential decreases in stimulus sections 1 and 2 and almost reaches the resting potential again in section 3. In contrast to Variant A, the membrane depolarization of Variant B is a monotonic function of brightness. In stimulus section 1, the cell is already fully saturated (i.e. depolarized beyond −25 mV). Note that by design, wild-type ChR would behave the same as Variant B, shifted 2 log units to darker intensity values.

Bottom Line: Currently existing variants of channelrhodopsin--engineered for use in neurophysiological research--do not necessarily support the goal of vision restoration optimally, due to two factors: First, the nature of the light stimulus is fundamentally different in "optogenetic vision" compared to "optogenetic neuroscience".In this study, by using a computational model, we investigate properties of channelrhodopsin that might improve successful vision restoration.Furthermore, the computational model used for this study is provided as an interactive tool for the research community.

View Article: PubMed Central - PubMed

Affiliation: Centre for Integrative Neuroscience & Bernstein Center for Computational Biology, University Tübingen, Tübingen, Germany.

ABSTRACT
Some hereditary diseases, such as retinitis pigmentosa, lead to blindness due to the death of photoreceptors, though the rest of the visual system might be only slightly affected. Optogenetics is a promising tool for restoring vision after retinal degeneration. In optogenetics, light-sensitive ion channels ("channelrhodopsins") are expressed in neurons so that the neurons can be activated by light. Currently existing variants of channelrhodopsin--engineered for use in neurophysiological research--do not necessarily support the goal of vision restoration optimally, due to two factors: First, the nature of the light stimulus is fundamentally different in "optogenetic vision" compared to "optogenetic neuroscience". Second, the retinal target neurons have specific properties that need to be accounted for, e.g. most retinal neurons are non-spiking. In this study, by using a computational model, we investigate properties of channelrhodopsin that might improve successful vision restoration. We pay particular attention to the operational brightness range and suggest strategies that would allow optogenetic vision over a wider intensity range than currently possible, spanning the brightest 5 orders of naturally occurring luminance. We also discuss the biophysical limitations of channelrhodopsin, and of the expressing cells, that prevent further expansion of this operational range, and we suggest design strategies for optogenetic tools which might help overcoming these limitations. Furthermore, the computational model used for this study is provided as an interactive tool for the research community.

Show MeSH
Related in: MedlinePlus