Single Photon-Evoked Events Of The Ventral Nerve Photoreceptor Cell Of Limulus Facilitation, Adaptation And Dependence Of Lowered External Calcium

1991 ◽  
Vol 46 (5-6) ◽  
pp. 461-486 ◽  
Author(s):  
H. Stieve ◽  
H. Reuß ◽  
H. T. Hennig ◽  
J. Klomfaß
Keyword(s):  
Calcium Concentration ◽  
Calcium Release ◽  
Light Adaptation ◽  
Single Photon ◽  
Calcium Deficiency ◽  
Magnesium Concentration ◽  
Calcium Stores ◽  
Calcium Dependent ◽  
Ventral Nerve Photoreceptor ◽  
External Calcium

Bumps, the elementary excitatory events of the Limulus ventral nerve photo receptor following a weak flash of light were recorded under voltage clamp conditions. The statistical distribution of various bump parameters and their changes caused by weak conditioning pre-illumination are described, and the influence of lowered external Ca2+-concentration together with normal or raised Mg2+-concentration (15 °C).1) Weak conditioning pre-illumination causes desensitization: the bump current amplitude, bump duration , bump area (current-integral), and the bump latency are diminished, the more, the stronger the conditioning flash, i.e. the light adaptation. Very weak conditioning pre-illumination causes facilitation, expressed by an increase in number and size of the observed bumps. The average bump latency, however, is already shortened under these conditions.2) Lowering the external Ca2+-concentration from 10 mmol/l to 250 (µmol/1 has its primary effect on the dark -adapted photoreceptor (without substantially reducing the ability for light adaptation ). It causes the following average changes: the amplitudes, durations, current-integrals, and the latencies of current bumps are greatly enlarged and the number of bumps is raised.3) Raised magnesium concentration from 50 to 100 mmol/l can partially compensate for the lack of calcium ; however, it enhances the effect of calcium deficiency on the latency, i.e. it further enlarges the average latencies. The results can be explained on the basis of our model of bump generation by two assumptions.1) Lowering the external calcium concentration causes a decrease in the cytosolic Ca2+-level without substantially reducing the intracellular calcium stores from which the light-adapting calcium release is fed. The lowered cytosolic Ca2+-concentration induces an “extra” dark adaptation resulting in greater bumps and more bumps exceeding the threshold of recognition. The bump latency, however, which behaves differently from all other bump parameters, is determined by a separate calcium -dependent reaction where magnesium competes with calcium antagonistically. 2) Facilitation is due to cooperativity of transmitter binding in order to open the ion channels

The Effect of Changed Extracellular Calcium and Sodium Concentration on the Electroretinogram of the Crayfish Retina

1980 ◽  
Vol 35 (3-4) ◽  
pp. 308-318 ◽  
Author(s):  
H. Stieve ◽  
I. Claßen-Linke
Keyword(s):  
Dark Adaptation ◽  
Time Course ◽  
Calcium Concentration ◽  
Light Adaptation ◽  
Sodium Concentration ◽  
Strong Increase ◽  
Calcium Stores ◽  
Half Time ◽  
Astacus Leptodactylus ◽  
External Calcium

Abstract The electroretinogram (ERG) of the isolated retina of the crayfish Astacus leptodactylus evoked by strong 10 ms light flashes at constant 5 min intervals was measured while the retina was continuously superfused with various salines which differed in Ca2+ -and Na+ -concentrations. The osmotic pressure of test- and reference-saline was adjusted to be identical by adding sucrose. Results: 1. Upon raising the calcium-concentration of the superfusate in the range of 20-150 mmol/l (constant Na+ -concentration: 208 mmol/l) the peak amplitude hmax and the half time of decay t2 of the ERG both decrease gradually up to about 50% in respect to the corresponding value in reference saline. 2. The recovery of the ERG due to dark adaptation following the “weakly light adapted state” is greatly diminished in high external [Ca2+]ex. 3. Lowering the external calcium-concentration (10 →1 mmol/l) causes a small increase in hmax and a strong increase of the half time of decay t2 (about 180%). Upon lowering the calcium concentration of the superfusate to about 1 nmol/l by 1 mmol/l of the calcium buffer EDTA, a slowly augmenting diminution of the ERG height hm SLX occurs. How­ever, a strong retardation of the falling phase of the ERG characterized by an increase in t2 occurs quickly. Even after 90 min stay in the low calcium saline the retina is still not inexcitable; hmax is 5 - 10% of the reference value. The diminution of hmax occurs about six-fold faster when the buffer concentration is raised to 10 mmol/l EDTA. 4. Additional lowering of the Na+ -concentration (208 →20.8 mmol/l) in a superfusate with a calcium concentration raised to 150 mmol/l causes a strong reduction of the ERG amplitude hmax to about 10%. 5. In a superfusate containing 1 nmol/l calcium such lowering of the sodium concentration (208 → 20.8 mmol/l) causes a diminution of the ERG height to about 40% and the shape of the ERG to become polyphasic; at least two maxima with different time to peak values are observed. Interpretation: 1. The similarity of effects, namely raising external calcium concentration and light adaptation on the one hand and lowering external calcium and dark adaptation on the other hand may indicate that the external calcium is acting on the adaptation mechanism of the photoreceptor cells, presumably by influencing the intracellular [Ca2+]. 2. The great tolerance of the retina against Ca2+ -deficiency in the superfusate might be effected by calcium stores in the retina which need high Ca2+ -buffer concentrations in the superfusate to become exhausted. 3. In contrast to the Limulus ventral nerve photoreceptor there does not seem to be an antagonis­ tic effect of sodium and calcium in the crayfish retina on the control of the light channels. 4. The crayfish receptor potential seems to be composed of at least two different processes. Lowering calcium-and lowering external sodium-concentration both diminish the height and change the time course of the two components to a different degree. This could be caused by in­ fluencing the state of adaptation and thereby making the two maxima separately visible.

Differences in Force-Frequency Relationships and Calcium Dependency Between Elasmobranch and Teleost Hearts

1988 ◽  
Vol 140 (1) ◽  
pp. 227-241 ◽  
Author(s):  
WILLIAM R. DRIEDZIC ◽  
HANS GESSER
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Calcium Concentration ◽  
Calcium Release ◽  
Isometric Force ◽  
Calcium Stores ◽  
Force Frequency ◽  
Force Development ◽  
Calcium Storage ◽  
Sea Raven ◽  
External Calcium

Ventricle strips from little skate (Raja erinacea), spiny dogfish (Squalus acanthias), black dogfish (Etmopterus spinax), sea raven (Hemitripterus americanus), cod (Gadus morhua), hagfish (Myxine glutinosa) and white sturgeon (Acipenser transmontanus) were mounted for isometric force recording. Force development was assessed as a function of external calcium concentration and frequency of contraction. Post-rest potentiation was determined in skate and the teleost species to assess indirectly calcium storage capacities. Sea raven and cod preparations were also treated with ryanodine to assess the importance of calcium release from the sarcoplasmic reticulum. Ventricle strips from skate and black dogfish showed a five-fold increase in force development when external calcium was raised from a physiological to a saturating level. Force development by ventricle strips from other species tested increased by only about 50% over the same range of calcium concentration. For all elasmobranchs tested, an elevation in frequency of contraction of ventricle strips resulted first in an increase and subsequently in a decrease in force development. The apices of the curves were well within the physiological range of heart rates exhibited by these species. Preparations from teleosts showed only a decrease in force development when contraction frequency was elevated. Skate ventricle strips exhibited a very marked post-rest potentiation at 3mmoll−1 external calcium. This protocol is considered to reflect the importance of intracellular calcium stores in the beat-to-beat maintenance of contractility. Sea raven and cod ventricle strips did not show any major post-rest potentiation, suggesting that calcium storage in hearts of these species is minimal. Ryanodine treatment had no effect upon sea raven and cod heart preparations. This approach further implies that calcium release from sarcoplasmic reticulum is not critical in these species.

Extracellular Calcium, Magnesium, and Sodium Ion Competition in the Conductance Control of the Photosensory Membrane of Limulus Ventral Nerve Photoreceptor

1978 ◽  
Vol 33 (7-8) ◽  
pp. 574-579 ◽  
Author(s):  
H. Stieve ◽  
M. Bruns
Keyword(s):  
Membrane Potential ◽  
Calcium Concentration ◽  
Sodium Concentration ◽  
Extracellular Calcium ◽  
Magnesium Concentration ◽  
Sodium Ions ◽  
Extracellular Calcium Concentration ◽  
Calcium Magnesium ◽  
Extracellular Sodium ◽  
Ventral Nerve Photoreceptor

Abstract The membrane potential in the dark and the saturated response height of the ventral nerve photoreceptor of Limulus was measured by an intracellular electrode while the external concentration of calcium, magnesium and sodium ions was varied. Decreasing the extracellular calcium concentration from 10-2 mol/l causes a calcium-dependent lowering of the dark membrane potential and at very low concentrations (<10-8 mol/l a reversal to ca. +5 to +11 mV, if the external magnesium concentration is also low. Also, the light response diminishes with decreasing extracellular calcium concentration and disappears at a concentration of 10-9 mol/l. External magnesium can substitute for certain properties of extracellular calcium. Lowering the extracellular sodium concentration from 543 mmol/l to 30 - 50 mmol/1 reduces the dark membrane potential and the light responses at normal calcium concentration, whereas at low calcium concentration it causes a substantial rise of both. Interpretation: The results are in accordance with our working hypothesis that a strong reduction of the external calcium (and magnesium) concentration causes a calcium concentration dependent opening of “ light channels” in the dark. Additional lowering the extracellular sodium concentration counteracts this effect; opening and closing of light channels is controlled by negative binding sites on the cell membrane for which calcium and sodium ions compete with an antagonistic action.

scholarly journals The Effects of HCl and CaCl2 Injections on Intracellular Calcium and pH in Voltage-clamped Snail (Helix aspersa) Neurons

2002 ◽  
Vol 120 (4) ◽  
pp. 567-579 ◽  
Author(s):  
Roger C. Thomas
Keyword(s):  
Intracellular Ph ◽  
Calcium Concentration ◽  
Calcium Release ◽  
Cyclopiazonic Acid ◽  
Initial Response ◽  
Calcium Stores ◽  
Fluorescent Indicators ◽  
Rate Of Recovery ◽  
Ion Sensitive Microelectrodes ◽  
Snail Helix Aspersa

To investigate the mechanisms by which low intracellular pH influences calcium signaling, I have injected HCl, and in some experiments CaCl2, into snail neurons while recording intracellular pH (pHi) and calcium concentration ([Ca2+]i) with ion-sensitive microelectrodes. Unlike fluorescent indicators, these do not increase buffering. Slow injections of HCl (changing pHi by 0.1–0.2 pH units min−1) first decreased [Ca2+]i while pHi was still close to normal, but then increased [Ca2+]i when pHi fell below 6.8–7. As pHi recovered after such an injection, [Ca2+]i started to fall but then increased transiently before returning to its preinjection level. Both the acid-induced decrease and the recovery-induced increase in [Ca2+]i were abolished by cyclopiazonic acid, which empties calcium stores. Caffeine with or without ryanodine lowered [Ca2+]i and converted the acid-induced fall in [Ca2+]i to an increase. Injection of ortho-vanadate increased steady-state [Ca2+]i and its response to acidification, which was again blocked by CPA. The normal initial response to 10 mM caffeine, a transient increase in [Ca2+]i, did not occur with pHi below 7.1. When HCl was injected during a series of short CaCl2 injections, the [Ca2+]i transients (recorded as changes in the potential (VCa) of the Ca2+-sensitive microelectrode), were reduced by only 20% for a 1 pH unit acidification, as was the rate of recovery after each injection. Calcium transients induced by brief depolarizations, however, were reduced by 60% by a similar acidification. These results suggest that low pHi has little effect on the plasma membrane calcium pump (PMCA) but important effects on the calcium stores, including blocking their response to caffeine. Acidosis inhibits spontaneous calcium release via the RYR, and leads to increased store content which is unloaded when pHi returns to normal. Spontaneous release is enhanced by the rise in [Ca2+]i caused by inhibiting the PMCA.

scholarly journals Adaptation and facilitation in the barnacle photoreceptor.

1976 ◽  
Vol 67 (2) ◽  
pp. 235-276 ◽  
Author(s):  
M Hanani ◽  
P Hillman
Keyword(s):  
Calcium Concentration ◽  
Light Adaptation ◽  
High Sensitivity ◽  
Low Calcium ◽  
Channel Blocking ◽  
Time Courses ◽  
Ion Channel Blocking ◽  
Conditioning Intensity ◽  
Internal Calcium ◽  
External Calcium

The barnacle photoreceptor sensitivity may either decrease (light adaptation) or increase (facilitation) after exposure to a conditioning light. The balance between adaptation and facilitation is influenced by at least three factors: initial sensitivity state of the cell, external calcium concentration, and conditioning intensity. Cells of very high sensitivity show mainly adaptation, which appears only for higher conditioning intensities and is suppressed in low-calcium media. Less sensitive cells, or those whose sensitivity is reduced by injury or metabolic decay, exhibit facilitation, expecially in low-calcium media and at intermediate conditioning intensities. Both phenomena show recovery time-courses of seconds-to-minutes. Models are proposed which relate light adaptation, as previously suggested, to increased internal calcium concentration, and facilitation either to decreased internal calcium concentration or to decreased activation "affinity" of ion-channel-blocking sites.

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.

Effects of Calcium and Cyclopiazonic Acid on the Photoresponse in the Limulus Ventral Photoreceptor

1999 ◽  
Vol 54 (5-6) ◽  
pp. 446-455 ◽  
Author(s):  
Marlies Dorlöchter ◽  
Weijia Yuan ◽  
Hennig Stieve
Keyword(s):  
Calcium Concentration ◽  
Light Adaptation ◽  
Single Photon ◽  
Light Flash ◽  
Cyclopiazonic Acid ◽  
Cytosolic Calcium ◽  
Atpase Inhibitor ◽  
Fast Transient ◽  
Transient Elevation ◽  
Prolonged Response

Abstract 1. Single-photon responses (bumps) and small macroscopic photocurrents were studied in ventral photoreceptors of the horseshoe crab Limulus. Lowering the calcium concentration in the bath from 10 mᴍ to 250 μᴍ led to increased bump size. Adaptation of the cells by a moderately bright conditioning flash was not impaired. 2. Pressure-injection of 1.2 mᴍ EGTA into the dark-adapted cells resulted in reduced bump size. EGTA weakened the effect of the conditioning light flash although it did not completely abolish light adaptation. 3. The microsomal calcium-ATPase inhibitor cyclopiazonic acid strongly desensitized the cells, and bumps were suppressed below detection. When the bathing saline contained 10 mᴍ calcium, macroscopic photoresponses after extracellular application of the agent had amplitudes smaller than under control conditions but normal response kinetics: The response to a light step still consisted of a fast transient photocurrent and a much smaller plateau. However, when applied in calcium-free bathing saline, cyclopiazonic acid additionally influenced the waveform of the photoresponse. The clear distinction between transient and plateau was no longer possible, and the photocurrent appeared “square”. 4. Our results support the idea that a transient elevation of the cytosolic calcium concentration is obligatory for light adaptation in the ventral photoreceptor. It is also obligatory for the generation of the so-called C2 component of the photocurrent which is represented by “standard” bumps and the fast transient phase of a prolonged response. However, a rise in cytosolic calcium appears not necessary for the initiation of a slow electrical photoresponse.

scholarly journals Incomplete vesicular docking limits synaptic strength under high release probability conditions

eLife ◽  
2020 ◽  
Vol 9 ◽  
Author(s):  
Gerardo Malagon ◽  
Takafumi Miki ◽  
Van Tran ◽  
Laura C Gomez ◽  
Alain Marty
Keyword(s):  
Synaptic Vesicle ◽  
Synaptic Vesicles ◽  
Calcium Concentration ◽  
Site Occupancy ◽  
Calcium Entry ◽  
Maximum Output ◽  
Calcium Dependent ◽  
Maximum Value ◽  
Voltage Dependent ◽  
External Calcium

Central mammalian synapses release synaptic vesicles in dedicated structures called docking/release sites. It has been assumed that when voltage-dependent calcium entry is sufficiently large, synaptic output attains a maximum value of one synaptic vesicle per action potential and per site. Here we use deconvolution to count synaptic vesicle output at single sites (mean site number per synapse: 3.6). When increasing calcium entry with tetraethylammonium in 1.5 mM external calcium concentration, we find that synaptic output saturates at 0.22 vesicle per site, not at 1 vesicle per site. Fitting the results with current models of calcium-dependent exocytosis indicates that the 0.22 vesicle limit reflects the probability of docking sites to be occupied by synaptic vesicles at rest, as only docked vesicles can be released. With 3 mM external calcium, the maximum output per site increases to 0.47, indicating an increase in docking site occupancy as a function of external calcium concentration.

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