Ionic mechanisms of phototransduction in photoreceptor cells from the epistellar body of the octopus eledone cirrhosa

1999 ◽  
Vol 202 (8) ◽  
pp. 977-986
Author(s):  
C.S. Cobb ◽  
R. Williamson
Keyword(s):  
Time Course ◽  
Sea Water ◽  
Light Flash ◽  
Receptor Potential ◽  
Photoreceptor Cells ◽  
Evoked Response ◽  
Na Channel ◽  
External Application ◽  
Ionic Mechanisms ◽  
Potential Activity

Intracellular recordings were made from extraocular photoreceptor cells within isolated epistellar bodies of the lesser or northern octopus Eledone cirrhosa. The cells had resting potentials around −41+/−5 mV (mean +/− s.d., N=60) and showed light-flash-induced membrane depolarisation. The evoked response to a brief light flash consisted of a transient peak depolarisation, followed by a plateau component. The magnitude of the light-induced peak depolarisation response was decreased by bathing the epistellar body in artificial sea water (ASW) low in Na+, where choline+ replaced Na+, or by passing steady depolarising current. Replacement of external Na+ by Li+ had no effect on the light-stimulated response. The external application of the Na+ channel blocker tetrodotoxin (3 micromol l-1) increased the light-evoked response, but this was accompanied by a loss of action potential activity. The amplitude and duration of the response to a light flash was increased by bathing the epistellar body in ASW low in Ca2+, or in ASW containing 10 mmol l-1 Co2+, and after intracellular microinjection of the Ca2+ buffer EGTA. Intracellular microinjection of Ca2+ or inositol 1,4,5-trisphosphate, or external application of the phospholipase C inhibitor U-73122, had no apparent effect on the light-evoked response. These results are consistent with the interpretation that (1) the majority of the light-induced inward current is carried by Na+, probably via a non-selective cation channel, and (2) an increase in the intracellular free Ca2+ concentration, mediated by the phototransduction process, is involved in regulating the light-induced inward photocurrent and thus, in effect, determines the amplitude, time course and sensitivity of the receptor potential.

Photoreceptor cells with unusual functional properties on the ventral nerve of Limulus

1999 ◽  
Vol 16 (6) ◽  
pp. 1191-1197 ◽  
Author(s):  
KÁROLY NAGY ◽  
MARLIES DORLÖCHTER ◽  
SVENJA KLÄSEN ◽  
DANNY STEINBUSCH
Keyword(s):  
Time Course ◽  
Single Photon ◽  
Receptor Potential ◽  
Photoreceptor Cells ◽  
Light Sensitivity ◽  
Atpase Inhibitor ◽  
Decay Kinetics ◽  
Normal Cells ◽  
Inward Current ◽  
Low Efficiency

Normal photoreceptor cells on the ventral nerve of Limulus respond to a moderately intense flash with a large receptor potential or current. Occasionally, cells are found in which the same flash evokes only a small receptor potential or current. Our investigations reveal physiological reasons for the poor light sensitivity in these “unusual cells.” In unusual cells prolonged illumination with intense light evokes a step-like inward current with an amplitude of some nanoamperes, but without a large transient peak. The current appears to be summed up of single photon responses with amplitudes smaller than about 50 pA. Their time course is similar to that of small single photon responses forming the so-called macroscopic C1 component in normal cells. The macroscopic current evoked by an intense flash has slow activation and deactivation kinetics and reaches a saturated amplitude of about 4–5 nanoamperes. The light-intensity dependence of the current evoked by flashes or by prolonged illumination has a slope of about 1 in log–log plots. The decay kinetics of the current is similar to that of the C1 component measured in normal cells after the block of the C2 component. Occasionally, the step-like current is superposed by large standard bumps. These bumps are blocked by the Ca2+-ATPase inhibitor cyclopiazonic acid, while the sustained inward current persists. We conclude that in unusual cells the light-activated current is identical to the C1 component of normal cells. The phospholipase C pathway that in normal cells presumably gives rise to the C2 component functions only with a low efficiency in unusual cells.

scholarly journals Electrophysiological properties of isolated photoreceptors from the eye of Lima scabra.

1991 ◽  
Vol 97 (1) ◽  
pp. 17-34 ◽  
Author(s):  
E Nasi
Keyword(s):  
Light Adaptation ◽  
Sea Water ◽  
Bright Light ◽  
Receptor Potential ◽  
Input Resistance ◽  
Photoreceptor Cells ◽  
Continuous Illumination ◽  
Moderate Intensity ◽  
Electrophysiological Properties ◽  
Voltage Dependent

Photoreceptor cells were enzymatically dissociated from the eye of the file clam, Lima scabra. Micrographs of solitary cells reveal a villous rhabdomeric lobe, a smooth soma, and a heavily pigmented intermediate region. Membrane voltage recordings using patch electrodes show resting potentials around -60 mV. Input resistance ranges from 300 M omega to greater than 1 G omega, while membrane capacitance is of the order of 50-70 pF. In darkness, quantum bumps occur spontaneously and their frequency can be increased by dim continuous illumination in a fashion graded with light intensity. Stimulation with flashes of light produces a depolarizing photoresponse which is usually followed by a transient hyperpolarization if the stimulus is sufficiently intense. Changing the membrane potential with current-clamp causes the early phase to invert around +10 mV, while the hyperpolarizing dip disappears around -80 mV. With bright light, the biphasic response is followed by an additional depolarizing wave, often accompanied by a burst of action potentials. Both Na and Ca ions are required in the extracellular solution for normal photoexcitation: the response to flashes of moderate intensity is greatly degraded either when Na is replaced with Tris, or when Ca is substituted with Mg. By contrast, quantum bumps elicited by dim, sustained light are not affected by Ca removal, but they are markedly suppressed in a reversible way in 0 Na sea water. It was concluded that the generation of the receptor potential is primarily dependent on Na ions, whereas Ca is probably involved in a voltage-dependent process that shapes the photoresponse. Light adaptation by repetitive flashes leads to a decrease of the depolarizing phase and a concomitant enhancement of the hyperpolarizing dip, eventually resulting in a purely hyperpolarizing photoresponse. Dark adaptation restores the original biphasic shape of the photoresponse.

The pH Dependence of the Receptor Potential of the Hermit Crab Photoreceptor

1974 ◽  
Vol 29 (3-4) ◽  
pp. 147-156 ◽  
Author(s):  
H. Stieve ◽  
T. Malinowska
Keyword(s):  
Hermit Crab ◽  
Time Course ◽  
Compound Eye ◽  
Ph Dependence ◽  
Receptor Potential ◽  
Photoreceptor Cells ◽  
Alkaline Solutions ◽  
Ph Effects ◽  
Good Reproducibility ◽  
Acidic Environments

Abstract The pH dependence of the receptor potential (ReP) of isolated layers of photoreceptor cells from the hermit crab compound eye (Eupagurus bernhardus L.) was determined. Measurements were performed, using extracellular electrodes, in the range pH 3.5 - 9.5 in three different buffer systems: Tris, glycine, and phosphate. The amplitude of the ReP was highest at pH 7.5 and decreased in more acidic and more alka­line salines (Fig. 4). Relative to the changes in ReP amplitude, the changes in time course and shape of ReP were small. Salines of pH other than 7.5 caused an increase of the latent period but decreased the peak amplitude time and the repolarizing phase (t2). Alkaline salines caused about the same changes in the ReP as acidic salines. The only observed difference was that repolarisation was more strongly influenced by alkaline solutions and that the plateau magnitude was depressed relatively more than the peak magnitude in acidic environments. Of the three buffers used, Tris had the weakest influence on the ReP and phosphate buffer the strongest. In contrast to the good reproducibility of the experimental results, the reversibility of the pH effects was generally poor; the effects with glycine-buffer were more reversible than those with Tris.

The Sensitivity of the Ventral Nerve Photoreceptor of Limulus Recovers after Light Adaptation in Two Phases of Dark Adaptation

1986 ◽  
Vol 41 (5-6) ◽  
pp. 657-667 ◽  
Author(s):  
I. Claßen-Linke ◽  
H. Stieve
Keyword(s):  
Dark Adaptation ◽  
Time Course ◽  
Light Adaptation ◽  
Light Flash ◽  
Light Response ◽  
Receptor Potential ◽  
Second Phase ◽  
Two Phases ◽  
Ventral Nerve Photoreceptor ◽  
External Calcium

The time course of the recovery of the sensitivity of the Limulus ventral nerve photoreceptor was measured during dark adaptation following light adaptation by a bright 1 or 5 s illumination. The stimulus intensity ICR of a 300 μs light flash evoking a response of criterion amplitude (receptor potential or receptor current under voltage clamp conditions) was used as measure of sensitivity.The time course of dark adaptation shows two phases with time constants in the range of 5-9 s and 300-500 s (15 °C). Only the first of the two phases is significantly changed when the extracel- lular Ca2+-concentration is varied.The power function ICR = a·Io-tDA-b gives a good data fit for each of the two phases of dark adaptation. In the first phase the factor ax and the exponent bx are decreased when the external calcium is lowered from 10 mmol/1 to 250 μmol/1. Conversely a1 and b1 are increased when the Ca2+-concentration is raised to 40 mmol/1. For the second phase neither a2 nor b2 is changed significantly upon the changes in calcium concentration in the same experiments.The two phases of dark adaptation reflect the behaviour of the two components C1 and C2 of the electrical light response (receptor potential or receptor current). Under the conditions described here C, determines the size of the light response during the first phase of dark adaptation whereas C2 mainly influences the size of the response during the second phase.Interpretation: The fast first phase of dark adaptation is determined by the change in intracellu- lar Ca2+-concentration. The slower second phase of dark adaptation is not primarily calcium- controlled.

scholarly journals The Ventral Photoreceptor Cells of Limulus

1969 ◽  
Vol 54 (3) ◽  
pp. 310-330 ◽  
Author(s):  
Ronald Millecchia ◽  
Alexander Mauro
Keyword(s):  
Receptor Potential ◽  
Photoreceptor Cells ◽  
Regenerative Process ◽  
Resting Potential ◽  
Transient Phase ◽  
External Concentration ◽  
Slow Potential ◽  
Retinular Cells ◽  
Convenient Model ◽  
State Component

The ventral photoreceptors of Limulus polyphemus are unipolar cells with large, ellipsoidal somas located long both "lateral olfactory nerves." As a consequence of their size and location, the cells are easily impaled with microelectrodes. The cells have an average resting potential of -48 mv. The resting potential is a function of the external concentration of K. When the cell is illuminated, it gives rise to the typical "receptor potential" seen in most invertebrate photoreceptors which consists of a transient phase followed by a maintained phase of depolarization. The amplitude of the transient phase depends on both the state of adaptation of the cell and the intensity of the illumination, while the amplitude of the maintained phase depends only on the intensity of the illumination. The over-all size of the receptor potential depends on the external concentration of Na, e.g. in sodium-free seawater the receptor potential is markedly reduced, but not abolished. On the other hand lowering the Ca concentration produces a marked enhancement of both components of the response, but predominantly of the steady-state component. Slow potential fluctuations are seen in the dark-adapted cell when it is illuminated with a low intensity light. A spike-like regenerative process can be evoked by either the receptor potential or a current applied via a microelectrode. No evidence of impulse activity has been found in the axons of these cells. The ventral photoreceptor cell has many properties in common with a variety of retinular cells and therefore should serve as a convenient model of the primary receptor cell in many invertebrate eyes.

scholarly journals TRP and the PDZ Protein, Inad, Form the Core Complex Required for Retention of the Signalplex in Drosophila Photoreceptor Cells

2000 ◽  
Vol 150 (6) ◽  
pp. 1411-1422 ◽  
Author(s):  
Hong-Sheng Li ◽  
Craig Montell
Keyword(s):  
Transient Receptor Potential ◽  
Direct Interaction ◽  
Light Response ◽  
Receptor Potential ◽  
Photoreceptor Cells ◽  
Macromolecular Complex ◽  
Pdz Domains ◽  
The Core ◽  
Transient Receptor ◽  
Drosophila Photoreceptor

The light response in Drosophila photoreceptor cells is mediated by a series of proteins that assemble into a macromolecular complex referred to as the signalplex. The central player in the signalplex is inactivation no afterpotential D (INAD), a protein consisting of a tandem array of five PDZ domains. At least seven proteins bind INAD, including the transient receptor potential (TRP) channel, which depends on INAD for localization to the phototransducing organelle, the rhabdomere. However, the determinants required for localization of INAD are not known. In this work, we showed that INAD was required for retention rather than targeting of TRP to the rhabdomeres. In addition, we demonstrated that TRP bound to INAD through the COOH terminus, and this interaction was required for localization of INAD. Other proteins that depend on INAD for localization, phospholipase C and protein kinase C, also mislocalized. However, elimination of any other member of the signalplex had no impact on the spatial distribution of INAD. A direct interaction between TRP and INAD did not appear to have a role in the photoresponse independent of localization of multiple signaling components. Rather, the primary function of the TRP/ INAD complex is to form the core unit required for localization of the signalplex to the rhabdomeres.

The Effects of External Salinity on the Drinking Rates of the Larvae of Herring, Plaice and Cod

1988 ◽  
Vol 138 (1) ◽  
pp. 1-15 ◽  
Author(s):  
P. TYTLER ◽  
J. H. BLAXTER
Keyword(s):  
Time Course ◽  
Gadus Morhua ◽  
Sea Water ◽  
Fluorescein Isothiocyanate ◽  
Yolk Sac ◽  
Clupea Harengus ◽  
Larval Stages ◽  
First Feeding ◽  
Fluorescein Isothiocyanate Dextran ◽  
External Salinity

Drinking responses to salinity change in the larvae of herring (Clupea harengus L.), plaice (Pleuronectes platessa L.) and cod (Gadus morhua L.) were measured from the time course of uptake of dextran labelled with tritium, following immersion in solutions of 32‰ and 16‰ sea water. The yolk sac and first feeding larval stages of all three species drink in both salinities. Furthermore, post-yolk sac stages appear to adjust their drinking rates to compensate for different salinities in a manner similar to that of the adults. Drinking rates in 32‰ sea water are approximately double those in 16‰. Mass-related drinking rates of larvae are higher than those in adults, but the differences do not match the differences in surface area to mass ratios, suggesting that larval skin is less permeable to water than is adult gill epithelium. Water absorption is indicated by the evidence of concentration of dextran in the gut. The estimates of drinking rates from tritiated dextran uptake are supported by epifluorescence microscopical measurements of the uptake of fluorescein isothiocyanate dextran.

Laminar excitability cycles in neocortex

1991 ◽  
Vol 65 (4) ◽  
pp. 891-898 ◽  
Author(s):  
D. S. Barth ◽  
S. Di
Keyword(s):  
Time Course ◽  
Microelectrode Array ◽  
Cortical Excitability ◽  
Initial Period ◽  
Current Source ◽  
Conditioning Stimulus ◽  
Principal Component ◽  
Evoked Response ◽  
Rat Somatosensory Cortex ◽  
The Relationship

1. Laminar field potentials produced by paired electrocortical stimuli were recorded with a linear microelectrode array inserted perpendicular to the surface of rat somatosensory cortex. Current source-density (CSD) distributions of the direct cortical response (DCR) were computed from the potential profiles. Principal component analysis (PCA) was used to estimate the time course of evoked transmembrane currents of putative pyramidal cell populations in the supragranular and infragranular layers. 2. Both supra- and infragranular cells displayed an initial period after the conditioning stimulus in which test stimuli produced subnormal evoked response amplitudes. This was followed in both layers by a long period of supernormal then subnormal responses and a second period of supernormal responses. 3. The main laminar difference encountered was a general shortening of all phases of the excitability cycle in the supragranular cells. 4. Excitability cycles in the supra- and infragranular layers closely followed the morphology of average evoked responses to the conditioning stimulus alone. These results and physiological support to the validity of lamina-specific evoked response waveforms derived from combined CSD and PCA analysis of extracellular potential measurements. 5. The relationship between evoked potential amplitude changes and cortical excitability is discussed.

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