Limits...
Cellular elements for seeing in the dark: voltage-dependent conductances in cockroach photoreceptors.

Salmela I, Immonen EV, Frolov R, Krause S, Krause Y, Vähäsöyrinki M, Weckström M - BMC Neurosci (2012)

Bottom Line: Two voltage-dependent potassium conductances were found in the photoreceptors: a delayed rectifier type (KDR) and a fast transient inactivating type (KA).However, larger KA conductances were found in smaller and rapidly adapting photoreceptors, where KA could have a functional role.In general, the varying deployment of stereotypical K+ conductances in insect photoreceptors highlights their functional flexibility in neural coding.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physics, University of Oulu, Oulu, Finland.

ABSTRACT

Background: The importance of voltage-dependent conductances in sensory information processing is well-established in insect photoreceptors. Here we present the characterization of electrical properties in photoreceptors of the cockroach (Periplaneta americana), a nocturnal insect with a visual system adapted for dim light.

Results: Whole-cell patch-clamped photoreceptors had high capacitances and input resistances, indicating large photosensitive rhabdomeres suitable for efficient photon capture and amplification of small photocurrents at low light levels. Two voltage-dependent potassium conductances were found in the photoreceptors: a delayed rectifier type (KDR) and a fast transient inactivating type (KA). Activation of KDR occurred during physiological voltage responses induced by light stimulation, whereas KA was nearly fully inactivated already at the dark resting potential. In addition, hyperpolarization of photoreceptors activated a small-amplitude inward-rectifying (IR) current mediated at least partially by chloride. Computer simulations showed that KDR shapes light responses by opposing the light-induced depolarization and speeding up the membrane time constant, whereas KA and IR have a negligible role in the majority of cells. However, larger KA conductances were found in smaller and rapidly adapting photoreceptors, where KA could have a functional role.

Conclusions: The relative expression of KA and KDR in cockroach photoreceptors was opposite to the previously hypothesized framework for dark-active insects, necessitating further comparative work on the conductances. In general, the varying deployment of stereotypical K+ conductances in insect photoreceptors highlights their functional flexibility in neural coding.

Show MeSH

Related in: MedlinePlus

Outward currents in photoreceptors. Voltage-clamp recordings revealed of voltage-dependent outward currents that could be activated with depolarization the cell. The outward current consisted of at least two components, the amount of which varied between cells. A) A photoreceptor with large transient current B) A photoreceptor with both transient and sustained currents C) The sustained current did not inactivate during a 10 s long voltage clamp. Voltage was clamped from -47 mV to +3 mV with 10 mV intervals after a -117 mV prepulse. D) Depolarizing pulses from -57 to +3 mV given after a hyperpolarizing -117 mV pre-pulse elicited both a sustained and a transient outward current E) Positive prepulse inactivated the transient component, and subsequent depolarization activated only the sustained current. F) The transient current could be isolated by subtraction of the currents from protocols in D) and E). The scale bar applies for panels D, E, and F.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3472236&req=5

Figure 2: Outward currents in photoreceptors. Voltage-clamp recordings revealed of voltage-dependent outward currents that could be activated with depolarization the cell. The outward current consisted of at least two components, the amount of which varied between cells. A) A photoreceptor with large transient current B) A photoreceptor with both transient and sustained currents C) The sustained current did not inactivate during a 10 s long voltage clamp. Voltage was clamped from -47 mV to +3 mV with 10 mV intervals after a -117 mV prepulse. D) Depolarizing pulses from -57 to +3 mV given after a hyperpolarizing -117 mV pre-pulse elicited both a sustained and a transient outward current E) Positive prepulse inactivated the transient component, and subsequent depolarization activated only the sustained current. F) The transient current could be isolated by subtraction of the currents from protocols in D) and E). The scale bar applies for panels D, E, and F.

Mentions: Voltage clamp experiments revealed a voltage-activated outward current (Figure 2) responsible for the rectification observed at depolarized voltages in current clamp recordings (Figure 1E). Kinetics and amplitude of the outward current varied from cell to cell (Figure 2A-B). In approximately half of the photoreceptors, the current clearly consisted of two components: a fast-activating transient current and a slow-activating sustained current (Figure 2B). The sustained current showed no inactivation during prolonged voltage pulses (Figure 2C).


Cellular elements for seeing in the dark: voltage-dependent conductances in cockroach photoreceptors.

Salmela I, Immonen EV, Frolov R, Krause S, Krause Y, Vähäsöyrinki M, Weckström M - BMC Neurosci (2012)

Outward currents in photoreceptors. Voltage-clamp recordings revealed of voltage-dependent outward currents that could be activated with depolarization the cell. The outward current consisted of at least two components, the amount of which varied between cells. A) A photoreceptor with large transient current B) A photoreceptor with both transient and sustained currents C) The sustained current did not inactivate during a 10 s long voltage clamp. Voltage was clamped from -47 mV to +3 mV with 10 mV intervals after a -117 mV prepulse. D) Depolarizing pulses from -57 to +3 mV given after a hyperpolarizing -117 mV pre-pulse elicited both a sustained and a transient outward current E) Positive prepulse inactivated the transient component, and subsequent depolarization activated only the sustained current. F) The transient current could be isolated by subtraction of the currents from protocols in D) and E). The scale bar applies for panels D, E, and F.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3472236&req=5

Figure 2: Outward currents in photoreceptors. Voltage-clamp recordings revealed of voltage-dependent outward currents that could be activated with depolarization the cell. The outward current consisted of at least two components, the amount of which varied between cells. A) A photoreceptor with large transient current B) A photoreceptor with both transient and sustained currents C) The sustained current did not inactivate during a 10 s long voltage clamp. Voltage was clamped from -47 mV to +3 mV with 10 mV intervals after a -117 mV prepulse. D) Depolarizing pulses from -57 to +3 mV given after a hyperpolarizing -117 mV pre-pulse elicited both a sustained and a transient outward current E) Positive prepulse inactivated the transient component, and subsequent depolarization activated only the sustained current. F) The transient current could be isolated by subtraction of the currents from protocols in D) and E). The scale bar applies for panels D, E, and F.
Mentions: Voltage clamp experiments revealed a voltage-activated outward current (Figure 2) responsible for the rectification observed at depolarized voltages in current clamp recordings (Figure 1E). Kinetics and amplitude of the outward current varied from cell to cell (Figure 2A-B). In approximately half of the photoreceptors, the current clearly consisted of two components: a fast-activating transient current and a slow-activating sustained current (Figure 2B). The sustained current showed no inactivation during prolonged voltage pulses (Figure 2C).

Bottom Line: Two voltage-dependent potassium conductances were found in the photoreceptors: a delayed rectifier type (KDR) and a fast transient inactivating type (KA).However, larger KA conductances were found in smaller and rapidly adapting photoreceptors, where KA could have a functional role.In general, the varying deployment of stereotypical K+ conductances in insect photoreceptors highlights their functional flexibility in neural coding.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physics, University of Oulu, Oulu, Finland.

ABSTRACT

Background: The importance of voltage-dependent conductances in sensory information processing is well-established in insect photoreceptors. Here we present the characterization of electrical properties in photoreceptors of the cockroach (Periplaneta americana), a nocturnal insect with a visual system adapted for dim light.

Results: Whole-cell patch-clamped photoreceptors had high capacitances and input resistances, indicating large photosensitive rhabdomeres suitable for efficient photon capture and amplification of small photocurrents at low light levels. Two voltage-dependent potassium conductances were found in the photoreceptors: a delayed rectifier type (KDR) and a fast transient inactivating type (KA). Activation of KDR occurred during physiological voltage responses induced by light stimulation, whereas KA was nearly fully inactivated already at the dark resting potential. In addition, hyperpolarization of photoreceptors activated a small-amplitude inward-rectifying (IR) current mediated at least partially by chloride. Computer simulations showed that KDR shapes light responses by opposing the light-induced depolarization and speeding up the membrane time constant, whereas KA and IR have a negligible role in the majority of cells. However, larger KA conductances were found in smaller and rapidly adapting photoreceptors, where KA could have a functional role.

Conclusions: The relative expression of KA and KDR in cockroach photoreceptors was opposite to the previously hypothesized framework for dark-active insects, necessitating further comparative work on the conductances. In general, the varying deployment of stereotypical K+ conductances in insect photoreceptors highlights their functional flexibility in neural coding.

Show MeSH
Related in: MedlinePlus