scholarly journals Changes in Intracellular Free Calcium Concentration during Illumination of Invertebrate Photoreceptors

1974 ◽  
Vol 64 (6) ◽  
pp. 643-665 ◽  
Author(s):  
J. E. Brown ◽  
J. R. Blinks
Keyword(s):  
Light Adaptation ◽  
Light Stimulus ◽  
Electrical Response ◽  
Bright Light ◽  
Photoreceptor Cells ◽  
Ion Concentration ◽  
Free Calcium ◽  
Undetectable Level ◽  
Sequence Of Events ◽  
Intracellular Calcium Ion

Aequorin, which luminesces in the presence of calcium, was injected into photoreceptor cells of Limulus ventral eye. A bright light stimulus elicited a large increase in aequorin luminescence, the aequorin response, indicating a rise of intracellular calcium ion concentration, Cai. The aequorin response reached a maximum after the peak of the electrical response of the photoreceptor, decayed during a prolonged stimulus, and returned to an undetectable level in the dark. Reduction of Cao reduced the amplitude of the aequorin response by a factor no greater than 3. Raising Cao increased the amplitude of the aequorin response. The aequorin response became smaller when membrane voltage was clamped to successively more positive values. These results indicate that the stimulus-induced rise of Cai may be due in part to a light-induced influx of Ca and in part to release of Ca from an intracellular store. Our findings are consistent with the hypothesis that a rise in Cai is a step in the sequence of events underlying light-adaptation in Limulus ventral photoreceptors. Aequorin was also injected into photoreceptors of Balanus. The aequorin responses were similar to those recorded from Limulus cells in all but two ways: (a) A large sustained aequorin luminescence was measured during a prolonged stimulus, and (b) removal of extracellular calcium reduced the aequorin response to an undetectable level.

scholarly journals Timing of Ca2+ Release from Intracellular Stores and the Electrical Response of Limulus Ventral Photoreceptors to Dim Flashes

2000 ◽  
Vol 115 (6) ◽  
pp. 735-748 ◽  
Author(s):  
Richard Payne ◽  
James Demas
Keyword(s):  
Latent Period ◽  
Electrical Response ◽  
Cyclopiazonic Acid ◽  
Receptor Potential ◽  
Ion Concentration ◽  
Free Calcium ◽  
Flash Intensity ◽  
Stochastic Variation ◽  
Highly Correlated ◽  
Indicator Dyes

Light-induced release of Ca2+ from stores in Limulus ventral photoreceptors was studied using confocal fluorescence microscopy and the Ca2+ indicator dyes, Oregon green-5N and fluo-4. Fluorescence was collected from a spot within 4 μm of the microvillar membrane. A dual-flash protocol was used to reconstruct transient elevations of intracellular free calcium ion concentration (Cai) after flashes delivering between 10 and 5 × 105 effective photons. Peak Cai increased with flash intensity to 138 ± 76 μM after flashes delivering ∼104 effective photons, while the latent period of the elevation of Cai fell from ∼140 to 21 ms. The onset of the light-induced elevation of Cai was always highly correlated with that of the receptor potential. The time for Cai to exceed 2 μM was approximately equal to that for the receptor potential to exceed 8 mV (mean difference; 2.2 ± 6.4 ms). Cai was also measured during steps of light delivering ∼105 effective photons/s to photoreceptors that had been bleached with hydroxylamine so as to reduce their quantum efficiency. Elevations of Cai were detected at the earliest times of the electrical response to the steps of light, when a significant receptor potential had yet to develop. Successive responses exhibited stochastic variation in their latency of up to 20 ms, but the elevation of Cai and the receptor potential still rose at approximately the same time, indicating a shared process generating the latent period. Light-induced elevations of Cai resulted from Ca2+ release from intracellular stores, being abolished by cyclopiazonic acid (CPA), an inhibitor of endoplasmic reticulum Ca2+ pumps, but not by removal of extracellular Ca2+ ions. CPA also greatly diminished and slowed the receptor potential elicited by dim flashes. The results demonstrate a rapid release of Ca2+ ions that appears necessary for a highly amplified electrical response to dim flashes.

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.

scholarly journals An Electrogenic Sodium Pump in Limulus Ventral Photoreceptor Cells

1972 ◽  
Vol 59 (6) ◽  
pp. 720-733 ◽  
Author(s):  
J. E. Brown ◽  
J. E. Lisman
Keyword(s):  
Sodium Pump ◽  
Light Stimulus ◽  
Bright Light ◽  
Receptor Potential ◽  
Photoreceptor Cells ◽  
Intracellular Accumulation ◽  
Light Responses ◽  
Electrogenic Sodium Pump ◽  
Electrogenic Na Pump ◽  
Intracellular Ca

A hyperpolarization can be recorded intracellularly following either a single bright light stimulus or the intracellular injection of Na+. This after-hyperpolarization is abolished by bathing in 5 x 10-6 M strophanthidin or removal of extracellular K+. Both treatments also lead to a small, rapid depolarization of the dark-adapted cell. When either treatment is prolonged, light responses can still be elicited, although with repetitive stimuli the responses are slowly and progressively diminished in size. The rate of diminution is greater for higher values of [Ca++]out; with [Ca++]out = 0.1 mM, there is almost no progressive diminution of repetitive responses produced by either K+-free seawater or strophanthidin. We propose that an electrogenic Na+ pump contributes directly to dark-adapted membrane voltage and also generates the after-hyperpolarizations, but does not directly generate the receptor potential. Inhibition of this pump leads to intracellular accumulation of sodium ions, which in turn leads to an increase in intracellular Ca++ (provided there is sufficient extracellular Ca++). This increase in intracellular calcium probably accounts for the progressive decrease in the size of the receptor potential seen when the pump is inhibited.

Confocal imaging of calcium in intact ventricular muscle provides a new view of excitation-contraction coupling

1996 ◽  
Vol 54 ◽  
pp. 738-739
Author(s):  
W.G. Wier
Keyword(s):  
Local Control ◽  
Cardiac Tissue ◽  
Cell Function ◽  
Isolated Heart ◽  
Cardiac Cells ◽  
Confocal Imaging ◽  
Ion Concentration ◽  
Heart Cell ◽  
Free Calcium ◽  
Heart Cells

A fundamentally new understanding of cardiac excitation-contraction (E-C) coupling is being developed from recent experimental work using confocal microscopy of single isolated heart cells. In particular, the transient change in intracellular free calcium ion concentration ([Ca2+]i transient) that activates muscle contraction is now viewed as resulting from the spatial and temporal summation of small (∼ 8 μm3), subcellular, stereotyped ‘local [Ca2+]i-transients' or, as they have been called, ‘calcium sparks'. This new understanding may be called ‘local control of E-C coupling'. The relevance to normal heart cell function of ‘local control, theory and the recent confocal data on spontaneous Ca2+ ‘sparks', and on electrically evoked local [Ca2+]i-transients has been unknown however, because the previous studies were all conducted on slack, internally perfused, single, enzymatically dissociated cardiac cells, at room temperature, usually with Cs+ replacing K+, and often in the presence of Ca2-channel blockers. The present work was undertaken to establish whether or not the concepts derived from these studies are in fact relevant to normal cardiac tissue under physiological conditions, by attempting to record local [Ca2+]i-transients, sparks (and Ca2+ waves) in intact, multi-cellular cardiac tissue.

scholarly journals Injection of inositol trisphosphorothioate into Limulus ventral photoreceptors causes oscillations of free cytosolic calcium.

1991 ◽  
Vol 97 (6) ◽  
pp. 1165-1186 ◽  
Author(s):  
R Payne ◽  
B V Potter
Keyword(s):  
Membrane Potential ◽  
Calcium Release ◽  
Feedback Inhibition ◽  
Initial Response ◽  
Periodic Variation ◽  
Cytosolic Calcium ◽  
Ion Concentration ◽  
Free Calcium ◽  
Calcium Stores ◽  
Calcium Ion Concentration

Limulus ventral photoreceptors contain calcium stores sensitive to release by D-myo-inositol 1,4,5 trisphosphate (InsP3) and a calcium-activated conductance that depolarizes the cell. Mechanisms that terminate the response to InsP3 were investigated using nonmetabolizable DL-myo-inositol 1,4,5 trisphosphorothioate (InsPS3). An injection of 1 mM InsPS3 into a photoreceptor's light-sensitive lobe caused an initial elevation of cytosolic free calcium ion concentration (Cai) and a depolarization lasting only 1-2 s. A period of densensitization followed, during which injections of InsPS3 were ineffective. As sensitivity recovered, oscillations of membrane potential began, continuing for many minutes with a frequency of 0.07-0.3 Hz. The activity of InsPS3 probably results from the D-stereoisomer, since L-InsP3 was much less effective than InsP3. Injections of 1 mM InsP3 caused an initial depolarization and a period of densensitization similar to that caused by 1 mM InsPS3, but no sustained oscillations of membrane potential. The initial response to InsPS3 or InsP3 may therefore be terminated by densensitization, rather than by metabolism. Metabolism of InsP3 may prevent oscillations of membrane potential after sensitivity has recovered. The InsPS3-induced oscillations of membrane potential accompanied oscillations of Cai and were abolished by injection of ethyleneglycol-bis (beta-aminoethyl ether)-N,N'-tetraacetic acid. Removal of extracellular calcium reduced the frequency of oscillation but not its amplitude. Under voltage clamp, oscillations of inward current were observed. These results indicate that periodic bursts of calcium release underly the oscillations of membrane potential. After each burst, the sensitivity of the cell to injected InsP3 was greatly reduced, recovering during the interburst interval. The oscillations may, therefore, result in part from a periodic variation in sensitivity to a constant concentration of InsPS3. Prior injection of calcium inhibited depolarization by InsPS3, suggesting that feedback inhibition of InsPS3-induced calcium release by elevated Cai may mediate desensitization between bursts and after injections of InsPS3.

Bile canalicular contraction in the isolated hepatocyte doublet is related to an increase in cytosolic free calcium ion concentration

2008 ◽  
Vol 8 (3) ◽  
pp. 178-183 ◽  
Author(s):  
Sumio Watanabe ◽  
Masahiro Tomono ◽  
Makoto Takeuchi ◽  
Tsuneo Kitamura ◽  
Miyoko Hirose ◽  
...  
Keyword(s):  
Calcium Ion ◽  
Ion Concentration ◽  
Free Calcium ◽  
Cytosolic Free Calcium ◽  
Bile Canalicular Contraction ◽  
Calcium Ion Concentration

scholarly journals The gravistimulation-induced very slow Ca2+ increase in Arabidopsis seedlings requires MCA1, a Ca2+-permeable mechanosensitive channel

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Masataka Nakano ◽  
Takuya Furuichi ◽  
Masahiro Sokabe ◽  
Hidetoshi Iida ◽  
Hitoshi Tatsumi
Keyword(s):  
Calcium Ion ◽  
Channel Blocker ◽  
Upright Position ◽  
Ion Concentration ◽  
Early Event ◽  
Free Calcium ◽  
Permeable Channel ◽  
Mechanosensitive Ion Channel ◽  
And Function ◽  
Calcium Ion Concentration

AbstractGravity is a critical environmental factor affecting the morphology and function of plants on Earth. Gravistimulation triggered by changes in the gravity vector induces an increase in the cytoplasmic free calcium ion concentration ([Ca2+]c) as an early process of gravity sensing; however, its role and molecular mechanism are still unclear. When seedlings of Arabidopsis thaliana expressing apoaequorin were rotated from the upright position to the upside-down position, a biphasic [Ca2+]c-increase composed of a fast-transient [Ca2+]c-increase followed by a slow [Ca2+]c-increase was observed. We find here a novel type [Ca2+]c-increase, designated a very slow [Ca2+]c-increase that is observed when the seedlings were rotated back to the upright position from the upside-down position. The very slow [Ca2+]c-increase was strongly attenuated in knockout seedlings defective in MCA1, a mechanosensitive Ca2+-permeable channel (MSCC), and was partially restored in MCA1-complemented seedlings. The mechanosensitive ion channel blocker, gadolinium, blocked the very slow [Ca2+]c-increase. This is the first report suggesting the possible involvement of MCA1 in an early event related to gravity sensing in Arabidopsis seedlings.

Integrin receptor-mediated mobilisation of intranuclear calcium in rat osteoclasts

1993 ◽  
Vol 105 (1) ◽  
pp. 61-68 ◽  
Author(s):  
G. Shankar ◽  
I. Davison ◽  
M.H. Helfrich ◽  
W.T. Mason ◽  
M.A. Horton
Keyword(s):  
Cell Function ◽  
Bone Cells ◽  
Dynamic Equilibrium ◽  
Bone Matrix ◽  
Ion Concentration ◽  
Calcium Signal ◽  
Free Calcium ◽  
Integrin Receptor ◽  
Vitronectin Receptor ◽  
Alpha V Beta 3

Cell-matrix interactions have been shown to play an important role in regulating cell function and behaviour. In bone, where calcified matrix formation and resorption events are required to be in dynamic equilibrium, regulation of adhesive interactions between bone cells and their matrix is critical. The present study focuses on the osteoclast, the bone resorbing cell, as well as integrins, which are cell surface adhesion receptors that mediate osteoclast attachment to bone matrix. In osteoclasts, the most abundant integrin receptor is the vitronectin receptor (VNR, alpha v beta 3). The objective of the study was to investigate changes in intracellular calcium, a regulator of osteoclast function, following addition of peptides that bind integrins, in particular the alpha v beta 3 form of the vitronectin receptor (VNR), which is highly expressed in osteoclasts. The study demonstrated a unique spatial localisation of the calcium signal in response to cell membrane receptor occupancy by integrin ligands in rat osteoclasts. Addition of peptides with the Arg-Gly-Asp (RGD) sequence such as BSP-IIA, GRGDSP and GRGDS to rat osteoclasts evoked an immediate increase in free calcium ion concentration [Ca2+]i, localised to the nuclei and to the thin cytoplasmic skirt. These responses were inhibited by F11, a monoclonal antibody to the rat integrin beta 3 chain, as well as echistatin, a snake venom shown to colocalise with the alpha v chain in osteoclasts, suggesting that the calcium signal is mediated by the alpha v beta 3 form of VNR.(ABSTRACT TRUNCATED AT 250 WORDS)

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