Photoreceptor Plasma Membrane Research Articles

Experimental analysis of a neural system: two modeling approaches.

The retinal neural system in the catfish which transforms light intensity temporal variations into the horizontal cell potential is experimentally analyzed and modeled by two distinct methods. The first method involves testing the system with gaussian white-noisemodulated light intensity and the subsequent derivation of a mathematical model in terms of a Wiener functional series. The second method involves testing of the system by step and sinewave stimuli and the postulation of a set of nonlinear differential equations which are designed to fit these stimulus-response data. In this latter approach, the differential equations describe the usually assumed dynamic behavior of the component subsystems, such as photoreceptor and horizontal cell membranes in terms of properties of membrance resistance and capacitance. The system behavior is found to exhibit certain “small signal” nonlinearities such as dynamic asymmetry in the response as well as certain “large signal” nonlinearities. The two modeling approaches and the resulting models are compared and it is found that the functional model derived from the white-noise experiment, while it does not attempt to describe the underlying system structure as the differential equation does, produced, in general, more satisfactory results as far as the input-output behavior of the system is concerned. It is suggested that combination of the two approaches could be very fruitful in modeling a particular system.

Fatty acid composition and level of diacylglycerols and phosphoglycerides in brain and retina

The fatty acid composition of diacylglycerols of toad brain and retina is reported. In addition, the fatty acid composition of brain and retina phospholipids and of diacylglycerols and phospholipids from choroid is also presented. Retina diacylglycerol content is 7-fold that of the brain; fatty acid acyl groups are also more unsaturated in the former tissue. The diacylglycerols of the retina contain an unusually high amount of docosahexaenoate (42%), while arachidonate represents about 7%. Other major fatty acids are palmitate (19%) and stearate (20%). Brain diacylglycerols contain only 3% docosahexaenoate, while arachidonate represents about 27%. Other components are stearate (24%), palmitate (17%) and oleate (14%). In the retina, the fatty acid composition of phospholipids resembled that of diacylglycerols, and the total unsaturated components were greater than in diacylglycerols. The ratio docosahexaenoate to arachidonate in retina phospholipids and diacylglycerols was similar. On the contrary, the fatty acid composition in the phospholipids from brain and choroid was unlike that observed in their diacylglycerols. It is concluded that the unique characteristics of retina diacylglycerols may be related to a lipid metabolic differentiation developed to sustain the polar lipids of the photoreceptor cell membranes during their renewal process.

The thermal origin of spontaneous activity in the Limulus photoreceptor.

1. Discrete depolarizations of the photoreceptor cell membrane called discrete waves occur spontaneously and in response to illumination in the eye of the horseshoe crab, Limulus. Each light induced discrete wave is caused by the absorption of a single photon.2. The frequencies of spontaneous and light induced discrete waves were studied at different temperatures from 0 to 25 degrees C using a new method of counting them to avoid errors due to their temporal overlap.3. The frequency of spontaneous discrete waves followed the Arrhenius relationship with activation energy equal to 48.6 kcal.4. The frequency of the discrete waves caused by a fixed level of steady illumination was not significantly changed when the temperature of the cell was changed.5. The relationship of the frequency of spontaneous discrete waves to temperature was compared to a prediction based on the relationship of the quantum relative spectral sensitivity of the Limulus eye to the temperature of the eye. The prediction was in good agreement with observation and suggests that spontaneous discrete waves result from thermally induced cis to trans isomerizations of visual pigment molecules.

Über die Ionen-Abhängigkeit des Rezeptorpotentials der Retina von Astacus leptodactylus / The Ion-dependence of the Receptor Potential of the Visual Cell of the Crayfish

The mass response of the photoreceptor cells of the isolated crayfish-retina (Astacus leptodactylus) (receptor potential ReP) resulting from short and long light stimuli, has been measured with external electrodes. The ionic composition of the saline by which the preparation was perfused was changed and the influence of those changes on the ReP was measured under constant stimulus conditions. When all sodium ions are substituted by potassium ions, the height of the ReP is reversibly both decreased and shortened (Figs. 3 and 4). When all sodium ions are almost substituted by choline ions, (the remaining sodium concentration at the photoreceptor cells being less than 1 mMol/Z) the sensitivity to light adaptation is drastically and reversibly increased. Mainly due to light adaptation the ReP becomes smaller and shorter whereas the latency period increases (Figs. 5 - 8). If the concentration of extracellular calcium is reduced to less than 0.1 mMol/l, the decrease of the REP is considerably and reversibly slowed down while the increase of the REP remains almost unchanged (Fig. 9). If magnesium ions are also lacking the effect is even more pronounced (Figs. 10 and 11). All these changes of the ReP are probably due to actions of the ions on the membrane of the photoreceptor cells or its immediate vicinity. The results do not allow an unequivocal decision whether the ReP is due to an increased conductance (CIM) of the photoreceptor cell membrane or due to a change in the action of an electrogenic ion pump (EPM). But considering the results as a whole, and especially those from the low Ca- and low Mg-experiments, it seems unlikely that the ReP is caused by an EPM.

Membrane properties of a barnacle photoreceptor examined by the voltage clamp technique.

1. Electrical properties of the membrane of photoreceptor cells in the lateral ocelli of barnacles, Balanus amphitrite and B. eburneus were investigated by intracellular recording, polarization and voltage-clamp techniques.2. The resting potential of a dark adapted cell was 36.3 +/- 6.6 mV (S.D.) and depended mainly on the external K(+) concentration.3. Current-voltage relations obtained from voltage-clamp experiments in the absence of light were non-linear and varied with time after the onset of a step change in membrane potential; the steady state was reached after about 0.5 sec.4. Illumination resulted in a membrane potential change under current clamp and in a change of membrane current (light-initiated membrane current (L.I.C.): total membrane current with illumination minus current without illumination) under voltage-clamp conditions. Amplitudes and time course of L.I.C. depended on the light intensity as well as membrane potential.5. The L.I.C.-voltage relation was non-linear and corresponded with a slope conductance increase with increasing positive membrane potential.6. The reversal potential of L.I.C. was independent of the light intensity and the time after onset of illumination; the average value obtained in normal saline was +26.9 +/- 5.0 mV.7. The membrane conductance estimated from instantaneous L.I.C.-voltage relations agreed with the chord conductance of the non-linear L.I.C.-voltage relation.8. Decreasing external Na(+) concentration decreased the inward component of L.I.C. but not the outward component.9. Decreasing external Ca(2+) concentration increased the inward as well as the outward component of L.I.C.10. The reversal potential shifted in the negative direction with decreasing external Na(+) concentration (the rate was 10-15 mV for a tenfold change in concentration) and the rate was augmented in the absence of Ca(2+) but did not exceed 21 mV.11. The change of reversal potential with changes of external Ca(2+) concentration was negligible in normal Na(+) media but was significant in the absence of Na(+) (rate as high as 20 mV).12. Alteration of the external K(+) or Cl(-) concentrations did not affect the amplitude or reversal potential of L.I.C.13. The results indicate that illumination increases the membrane permeability mainly to Na(+) ions and that the primary effect of Ca(2+) ions is suppression of the permeability increase; Ca(2+) permeability may increase slightly during illumination.

A role for the sodium pump in photoreception in Limulus.

The membranes of photoreceptor cells in Limulus have an electrogenic sodium pump which contributes directly to membrane potential and whose activity is changed by light. These light-induced changes in pump activity underlie the receptor potential.

Photoelectric potential from photoreceptor cells in ventral eye of Limulus.

Intense colored light from a gas laser evokes a photoelectric potential in the photoreceptor cells of the ventral eye of Limulus. This potential has two components, both of which have the action spectrum of a rhodopsin with an absorbancy maximum at 530 nm. The evidence is consistent with the hypothesis that the photoelectric potential arises directly from the orderly array of rhodopsin molecules which are an integral part of the photoreceptor cell membrane.

Simultaneous recording of photoreceptor potentials and the PIII component of the ERG

Были зaпиcaны фoтopeцeптopныe пoтeнциaлы c пoмoщью микpoэлeкpoдoв oт ceтхaтки Necturus, пocлe изoляции кoмпoнeнтa P III элeктpopeтинoгpaммы (ЭpГ) хлopиcтым нaтpиeм и aзидoм. Пocкoлькy oбa пoтeнциaлa oбнapyживaют нeкoтopыe oбщиe хapaктepиcтики, тaкиe кaк вpeмя нaхaлa и oкoнхaния, пoляpнocть, кoнфигypaцию, peaкцию нa пpepывиcтyю cвeтoвyю cтимyляцию, дeлaeтcя зaклюхeниe o тoм, хтo фoтopeцeптopный пoтeнциaл и P III, oхeнь вepoятнo, являютcя пpoявлeниeм тoгo жe caмoгo пpoцecca. Из этoгo cлeдyeт, хтo фoтopeцe тopный пoтeнциaл мoжeт имeть тecнyю cвязь, ecли нe пpямo oпpeдeляeт вoлны a и d элeктpopeтинoгpaммы. Cиcтeмa элeмeнтoв, кoтopaя гeнepиpyeт эти пoтeнциaлы, вoзмoжнo нe лoкaлизyeтcя в тoй хacти мeмбpaны фoтopeцeптopнoй клeтки, кoтopaя пpoткнyтa зaпиcывaющим микpoэлeктpoдoм, пocкoлькy мaлыe кoлихecтвa pacтвopa KCl дoбaвлeнныe в cтeклoвиднoe тeлo yмeньшaют фoтopeцeптopный пoтeнциaл бeз зaмeтнoгo влияния нa ЭpГ, тoгдa кaк бoльшиe кoлихecтвa KCl, дocтaтoхныe для изoляции кoмпoнeнтa P III, дaют в peзyльтaтe иcхeзнoвeниe фoтopeцeптopнoгo пoтeнциaлa.