Single photon responses in locust photoreceptors: the effects of stimulus location on amplitude and time course

Pece, A. E. C.; French, Andrew S.

doi:10.1007/bf00612996

Cited by 3 publications

(5 citation statements)

References 17 publications

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“…In Limulus photoreceptors the average delay of single photon responses ("bumps") is twice their average duration, which has been shown to be incompatible with any cascade model in which there is gain at or before the first rate-limiting step (Schnakenberg and Keiper, 1986). However, the ratio between these two parameters is quite different for bumps from locust photoreceptors, for which the average delay is about equal to the average halfduration (Howard, 1983;Pece and French, 1989). The phototransduction process is much faster in insects than it is in Limulus, so that even if the biochemical components are the same, the detailed kinetic parameters are certainly quite different.…”

Section: Discussionmentioning

confidence: 99%

Nonlinear mechanisms for gain adaptation in locust photoreceptors

Pece

French

Korenberg

et al. 1990

Biophysical Journal

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Intracellular membrane potential responses were recorded from locust photoreceptors under two stimulus conditions: pairs of flashes to dark-adapted receptors, and white-noise modulated light at a range of background intensities from 500 to 15,000 effective photons per second. Nonlinear analysis of the input-output relationships were performed by estimating the Volterra and Wiener kernels of the system. The Volterra kernels obtained from the double-flash experiments were similar to the Wiener kernels obtained from the white-noise experiments, except for a change of time scale. The structure of the second-order kernels obtained with either method gave evidence for a gain control mechanism acting at an early stage of the cascade. Both feedforward and feedback nonlinearities could account for the observed system behavior at any one background level. The differences in amplitude between the kernels obtained at different background levels could be accounted for by an adaptation process which further decreased the gain of the system, acting on a slower time scale, also at some early stage of the cascade.

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Section: Discussionmentioning

confidence: 99%

Nonlinear mechanisms for gain adaptation in locust photoreceptors

Pece

French

Korenberg

et al. 1990

Biophysical Journal

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“…2 and 3 provide direct evidence for the fast spread of interaction between two flashes. Given the long electrotonic length constant of a locust photoreceptor (about 400 ~tm, according to Payne 1982, andFrench 1989), light-induced depolarization is almost uniform (within 5% between the two sites that we stimulated -Pece and French 1989) and therefore voltage-activated conductances are activated uniformly within the cell. Even if any kind of shunting conductance were to be activated locally, the long length constant would again ensure that it would provide an effective shunt for light responses occurring anywhere within the photoreceptor.…”

Section: Discussionmentioning

confidence: 99%

“…2 and 3 is that the stimuli were not localized because light scattering made the effective stimuli uniform in intensity over the length of the photoreceptor. Several pieces of evidence presented in a previous study (Pece and French 1989) indicate that the stimulus is localized in this preparation. However, since light scattering could seriously compromise the validity of the above experiment, we tried to obtain more evidence of stimulus localization.…”

Section: Localized Adaptationmentioning

confidence: 90%

“…2 and 3. By contrast, membrane depolarization spreads very fast, since the cell length constant is about 400 ~tm (Payne 1982;Pece and French 1989) and its time constant about 10 ms. Depolarization could mediate the observed depression in several different ways. The lightactivated conductance itself produces some self-shunting, but this is not sufficient to account for the observed depression, as was pointed out in the Introduction.…”

Section: Interaction Between Current Injection and Lightmentioning

confidence: 93%

“…For the in vitro experiments, the technique developed by Payne (1980Payne ( , 1982, as modified by Pece and French (1989) was used. Briefly, the head was isolated, then the upper part of the head was separated from the lower part and split with a sharp razor blade across both eyes, so that in each eye an array of photoreceptors were exposed across their length.…”

Section: Methodsmentioning

confidence: 99%

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Sublinear summation of responses in locust photoreceptors

Pece

French

1992

J Comp Physiol A

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Summary. The response of a locust, Locusta miyratoria,photoreceptor to a simultaneous pair of dim flashes is smaller than the sum of the responses to the individual component flashes, even when the photon absorption sites are separated by a distance of 120 ~tm, which should prevent them from interacting biochemically. A similar depression is observed when a flash is paired with a depolarizing current instead of a second flash, irrespective of whether the flash response precedes or follows the current response. These results indicate that the sublinear summation is caused by the activation of a voltageactivated shunting conductance. This conductance is not blocked by low intracellular concentrations of tetraethylammonium chloride, and is therefore different from the conductance which causes the decrease of the receptor's step response from transient to steady-state.

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Voltage-activated outward currents in adult and nymphal locust photoreceptors

Weckström

1994

J Comp Physiol A

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The membrane properties of dark-adapted green sensitive photoreceptors of adult and nymphal desert locust (Schistocerca gregaria) were investigated in situ with single electrode (discontinuous) current and voltage clamp techniques. The photoreceptors had a resting potential of about -70 mV. The membrane rectified strongly in response to depolarizing current pulses at and above the resting potential. Two outward currents could be distinguished on the basis of different kinetics. The first, a transient current, was inactivating between -40 mV and -100 mV, and activated above -90 mV. The second, a sustained current had a similar activation range. The inactivating current could be blocked by application of 50 mM TEA into the retinal extracellular space. Both currents were expressed in nymphal photoreceptors already in the 1st instar larva and have similar properties as in the adults, although the behaviour of adults and nymphs is different. The conductances underlying these currents could be shown to modify the frequency response of the photoreceptor membrane.

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Single photon responses in locust photoreceptors: the effects of stimulus location on amplitude and time course

Cited by 3 publications

References 17 publications

Nonlinear mechanisms for gain adaptation in locust photoreceptors

Nonlinear mechanisms for gain adaptation in locust photoreceptors

Sublinear summation of responses in locust photoreceptors

Voltage-activated outward currents in adult and nymphal locust photoreceptors

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