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Query: CAS:7440-70-2 (calcium)
 333,191 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Immature skeletal muscle cells, both in vivo and in vitro, express a high density of T type calcium current and a relatively low density of the dihydropyridine receptor, the protein thought to function as the Islow calcium channel and as the voltage sensor for excitation-contraction coupling. Although the role of the voltage sensor in eliciting elevations of myoplasmic, free calcium (calcium transients) has been examined, the role of the T type current has not. In this study we examined calcium transients associated with the T type current in cultured myotubes from normal and dysgenic mice, using the whole cell configuration of the patch clamp technique in conjunction with the calcium indicator dye Fluo-3. In both normal and dysgenic myotubes, the T type current was activated by weak depolarizations and was maximal for test pulses to approximately -20 mV. In normal myotubes that displayed T type calcium current, the calcium transient followed the amplitude and the integral of the current at low membrane potentials (-40 to -20 mV) but not at high potentials, where the calcium transient is caused by SR calcium release. The amplitude of the calcium transient for a pulse to -20 mV measured at 15 ms after depolarization represented, on average, 4.26 +/- 0.68% (n = 19) of the maximum amplitude of the calcium transient elicited by strong, 15-ms test depolarizations. In dysgenic myotubes, the calcium transient followed the integral of the calcium current at all test potentials, in cells expressing only T type current as well as in cells possessing both T type current and the L type current Idys. Moreover, the calcium transient also followed the amplitude and time course of current in dysgenic myotubes expressing the cardiac, DHP-sensitive calcium channel. Thus, in those cases where the transient appears to be a consequence of calcium entry, it has the same time course as the integral of the calcium current. Inactivation of the T type calcium current with 1-s prepulses, or block of the current by the addition of amiloride (0.3-1.0 mM) caused a reduction in the calcium transient which was similar in normal and dysgenic myotubes. To allow calculation of expected changes of intracellular calcium in response to influx, myotubes were converted to a roughly spherical shape (myoballs) by adding 0.5 microM colchicine to culture dishes of normal cells. Calcium currents and calcium transients recorded from myoballs were similar to those in normal myotubes.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Calcium transients associated with the T type calcium current in myotubes. 769 66

A confocal spot detection optical setup was used to record fluorescence signals in response to calcium pulses, elicited by flash photolysis of DM-nitrophen, with the calcium indicators CaOrange-5N and Fluo-3. Our results yield the following conclusions: [Ca2+] changes are almost perfect spikes at pCa 9 and broader transients followed by a step at pCa 7. The [Ca2+] spikes were used to measure the dissociation rate constant of the Ca2+ dyes. Experiments at pCa 7 were used to verify the kinetic rate constants of the dyes and to obtain those of DM-nitrophen. The association rate constant of this compound was found to be more than one order of magnitude faster than that suggested previously. CaOrange-5N was able to track changes in [Ca2+] more accurately than Fluo-3. This latter dye introduced severe distortions which preclude a quantitative deconvolution of the fluorescence transients into changes in the free [Ca2+].
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PMID:Detection of Ca(2+)-transients elicited by flash photolysis of DM-nitrophen with a fast calcium indicator. 775 92

Using a flow cytometric assay, conjugate formation between human peripheral blood mononuclear cells (PBMC) and three different human tumour cell lines has been analysed. Changes in the intracellular calcium levels of PBMC were monitored using the calcium sensitive dye Fluo-3. Target cell populations were distinguished by forward scatter or following loading with the fluorescent dye, SNARF-1. Intracellular calcium was expressed as a ratio of fluorescence of conjugated to unconjugated PBMC and followed for ten minutes after initiation of conjugation. The results demonstrate an apparent increase in intracellular calcium in PBMC conjugated to the NK-sensitive cell line K562, and that the kinetics and magnitude of this response varied considerably between individuals. Tumour cells which were resistant to lysis (as determined in a 4 h chromium release assay) were also capable of eliciting a calcium response from PBMC. Although the induction of a rise in intracellular calcium was therefore not correlated with cytotoxicity, it was greater in IL-2-activated PBMC upon exposure to the same target cell lines as PBMC.
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PMID:Flow cytometric determination of intracellular calcium changes in human peripheral blood mononuclear cells during conjugation to tumour cell lines. 783 85

The suprachiasmatic nucleus (SCN) of the hypothalamus contains a circadian pacemaker responsible for several circadian rhythms. Retinal cell projections to the SCN carry light information that phase shifts the pacemaker through the release of excitatory amino acids. To study this pathway, the Ca(2+)-sensitive dyes Fluo-3 and Fura-2 were used in organotypic slice cultures of rat SCN to visualize changes in intracellular Ca2+ of individual cells. After at least two weeks of culture, Ca2+ responses were measured in response to agonists of glutamate receptors in the presence of tetrodotoxin (TTX). Cells that showed a Ca2+ increase in response to N-methyl-D-aspartate (NMDA) and non-NMDA agonists also showed immunoreactivity towards vasoactive intestinal peptide (VIP), providing further evidence that VIP-containing neurons receive direct retinal input. The cells differed in their responses to the NMDA and non-NMDA agonists, suggesting that the cells contain differing densities of glutamate receptor subtypes.
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PMID:Calcium imaging in organotypic cultures of the rat suprachiasmatic nucleus. 784 72

The expression of GABAB receptors in cultured mouse cerebellar granule cells was investigated in binding experiments using [3H](S,R)-baclofen as well as in functional assessment of the ability of (R)-baclofen to interact with depolarization (15-40 mM KCl) coupled changes in intracellular Ca2+ homeostasis and neurotransmitter release. In the latter case a possible functional coupling between GABAA and GABAB receptors was investigated. The binding studies showed that the granule cells express specific binding sites for (R)-baclofen. The number of binding sites could be increased by exposure of the cells to the GABAA receptor agonist THIP (4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol) during the culture period. Pretreatment of the neurons with pertussis toxin showed that the GABAB receptors are coupled to G-proteins. This coupling was, however, less pronounced when the cells had been cultured in the presence of THIP. When 45Ca2+ uptake was measured or the intracellular Ca2+ concentration ([Ca2+]i) determined using the fluorescent Ca2+ chelator Fluo-3 it could be demonstrated that culturing the neurons in THIP influences intracellular Ca2+ homeostasis. Moreover, this homeostasis was found to be functionally coupled to the GABAB receptors as (R)-baclofen inhibited depolarization-induced increases in 45Ca2+ uptake and [Ca2+]i. (R)-Baclofen also inhibited K(+)-induced transmitter release from the neurons as monitored by the use of [3H]D-aspartate which labels the neurotransmitter pool of glutamate. Using the selective GABAA receptor agonist isoguvacine it could be demonstrated that the GABAB receptors are functionally coupled to GABAA receptors in the neurons leading to a disinhibitory action of GABAB receptor agonists.
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PMID:Role of GABAB receptors in intracellular Ca2+ homeostasis and possible interaction between GABAA and GABAB receptors in regulation of transmitter release in cerebellar granule neurons. 789

To determine the spatiotemporal pattern of hippocampal pyramidal cell activity during development, we examined cytosolic Ca2+ dynamics in tissue slices derived from early postnatal rats. After a brief (12-60 h) culture period, slices were stained with a calcium-sensitive dye, Fluo-3. Fluorescence imaging of the Fluo-3-stained slices with a scanning laser confocal microscope afforded simultaneous observation of many cells at high spatial resolution. Time-lapse imaging revealed spontaneous Ca2+ transients in the somata dendrites of many pyramidal cells in areas CA1 and CA3. For the most part, Ca2+ activity in neighboring pyramidal cells appeared to be uncorrelated, although we occasionally observed synchronous Ca2+ transients in adjacent cells. The transients were blocked by both tetrodotoxin (1 microM) and a mixture of the glutamate receptor antagonists, APV (50 microM) + CNQX (10 microM). Thus, spontaneous Ca2+ transients appear to be a consequence of activity-dependent release of glutamate acting postsynaptically through ionotropic glutamate receptors. Although gamma-aminobutyric acid (GABA) is thought to be an excitatory neurotransmitter during hippocampal development (Cherubini et al., 1991, Trends Neurosci. 14 (12):515-519), the spontaneous Ca2+ transients were not blocked by the GABAA receptor antagonist picrotoxin (100 microM). Furthermore, application of GABA (50 microM) abolished the spontaneous Ca2+ events, possibly via GABAB receptor-mediated inhibition of postsynaptic cells. The present results join other recent observations suggesting that isolated neural tissues support spontaneous activity, although the patterns and mechanisms of the activity reported here appear to differ from those of previous studies. Differences in the patterns of spontaneous activity during development may contribute to variations in the functional organization of different regions of CNS tissue.
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PMID:Spontaneous Ca2+ transients in developing hippocampal pyramidal cells. 791 Aug 45

Confocal laser scanning microscopy was used to analyze alterations in nuclear free calcium (Ca2+n) levels induced by platelet-derived growth factor (PDGF) isoforms in BALB/c3T3 fibroblasts loaded with the calcium-sensitive fluorescent indicator Fluo-3. Both AA-PDGF and BB-PDGF caused a transient increase in Ca2+n. Analysis of PDGF-induced Ca2+n alterations as a function of time revealed that BB-PDGF stimulation resulted in the generation of Ca2+n oscillations that diminished over time. The frequency of BB-PDGF-stimulated oscillations was modulated by extracellular Ca2+ and could not be mimicked by increasing intracellular inositol 1,4,5-trisphosphate levels in the absence of growth factor stimulation. Caffeine alone had no effect on Ca2+n levels, but exposure of cells to caffeine after BB-PDGF stimulation augmented Ca2+n oscillations, either by increasing the frequency or reinitiating preexisting oscillations. The genesis of these oscillations in Ca2+n appears to be in the region just outside of the nucleus, as perinuclear cytoplasmic free calcium (Ca2+i) increased just prior to Ca2+n. In contrast, AA-PDGF stimulation resulted in the generation of one or two irregular, transient Ca2+n spikes. Caffeine pretreatment followed by AA-PDGF stimulation resulted in Ca2+n oscillations very similar to those produced by BB-PDGF alone. Additionally, the AA-PDGF and BB-PDGF isoforms appeared to modulate distinct pools of cellular Ca2+, as BB-PDGF was still capable of inducing Ca2+n oscillations subsequent to prior induction of oscillations by AA-PDGF/caffeine. These PDGF isoform-specific changes in nuclear free Ca2+ could serve as a mechanism by which isoform-specific cellular signaling pathways may be manifested by the growth factors.
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PMID:Isoform-specific induction of nuclear free calcium oscillations by platelet-derived growth factor. 792 53

1. Ionic currents and the cytosolic free calcium concentration ([Ca2+]i) were recorded in rat hippocampal neurons in culture using the whole-cell configuration of the patch-clamp technique and confocal laser scanning microscopy with the fluorescent Ca2+ indicator Fluo-3 or dual-emission microspectrofluorimetry with the fluorescent Ca2+ indicator Indo-1. The excitatory amino acids, kainate and N-methyl-D-aspartate (NMDA), were repeatedly applied to the neurons using either a fast perfusion system or pressure-ejection from micropipettes. 2. Conditioning (1-10 s) applications of NMDA induced desensitization of NMDA currents. Recovery from desensitization, estimated from analysis of the amplitudes of short (20-50 ms) test NMDA currents, was double exponential. The time constant of the first phase was < 2 s and for the second phase it was in the range 10-50 s. 3. Conditioning applications of kainate decreased the amplitude of NMDA currents. Recovery of NMDA currents from kainate-induced inactivation was slow and could be fitted with a single exponential. The time constant of recovery was in the range 10-50 s and increased with prolongation of the conditioning pulse of kainate. 6-Cyano-7-nitroquinoxaline-2,3-dione (CNQX; 20 microM) prevented kainate-induced inactivation of NMDA currents. 4. Depolarizing voltage pulses (1-10 s) also induced an inactivation of NMDA currents with a slow recovery. The time course of the recovery increased with prolongation of depolarizing pulses and with an elevation of external calcium. Cadmium, a blocker of voltage-gated channels, prevented development of the depolarization-induced inactivation of NMDA currents. 5. Simultaneous recording of ionic currents and fluorescence of Ca(2+)-sensitive dyes showed that application of kainate, NMDA, or depolarizing pulses resulted in a rise of [Ca2+]i. Cadmium (100 microM) reversibly blocked [Ca2+]i transients induced by depolarizing pulses without modification of kainate-induced rise in fluorescence intensity. 6. For equal inward currents the elevation of [Ca2+]i was approximately 3.5-fold higher for applications of NMDA than for kainate. 7. Strong buffering of [Ca2+]i prevented the inactivation of NMDA currents induced by kainate or by depolarization. 8. Our results suggest that in the hippocampal neurons kainate produces inactivation of NMDA currents via an elevation of [Ca2+]i.
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PMID:Kainate-induced inactivation of NMDA currents via an elevation of intracellular Ca2+ in hippocampal neurons. 796 27

1. We investigated the effects of metabotropic glutamate (mGlu) receptor activation on intracellular Ca2+ concentration ([Ca2+]i) in the soma and dendrites of hippocampal CA1 pyramidal neurons. Changes in [Ca2+]i were measured using confocal imaging simultaneously with whole-cell recording techniques. Differences in [Ca2+]i were visualized as changes in the fluorescence of the Ca(2+)-sensitive dye Fluo-3. 2. Brief application of the specific mGlu receptor agonist (1S,3R)-ACPD to either the apical or basal dendrites produced initially localized increases in [Ca2+]i that subsequently propagated as waves throughout much of the neuron. These Ca2+ waves, which propagated at approximately 40 microns/s, were shown not to reflect intracellular Ca2+ diffusion or extracellular diffusion of ACPD and were always accompanied by small outward membrane currents. 3. Repetitive application of ACPD failed to trigger further Ca2+ release. We found that a threshold level of voltage-gated Ca2+ entry during trains of action potentials was needed to prime further mGlu-stimulated Ca2+ release. In contrast, the passage of time alone did not cause the mGlu-release system to reactivate--restoration of ACPD-stimulated Ca2+ release. The spike-mediated Ca2+ signal was unaffected by mGlu-stimulated depletion of intracellular stores. 4. These experiments demonstrate that specific mGlu receptor activation can mobilize Ca2+ in dendrites of CA1 neurons and trigger waves of Ca(2+)-induced Ca(2+)-release throughout the cell. A use-dependent relationship between voltage-gated Ca2+ entry during trains of action potentials and mGlu-stimulated Ca2+ release is suggested.
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PMID:Metabotropic glutamate receptor activation induces calcium waves within hippocampal dendrites. 796 30

1. The fluorescent dye fluo-3, in its permeant acetoxymethyl form, was used to monitor calcium transients during twitch and tetanus of single fibres isolated from the anterior tibialis muscle of Rana temporaria (2-5 degrees C). 2. Fluo-3 was loaded into the muscle fibre by diffusion. Under the experimental conditions used, approximately 45% of maximal fluorescence was reached during a 1 s fused isometric tetanus. Fluo-3 had no detectable effect on the mechanical response of the fibre. 3. The free calcium concentration in the myoplasm, [Ca2+]i, and its variation with time, was calculated from the fluorescence signal by accounting for the on- and off-rate constants for the binding of calcium to the dye. The time course of the calcium transient during twitch and tetanus determined in this way agreed well with previous measurements based on fast-reacting calcium-sensitive dyes. 4. [Ca2+]i declined steeply during the initial phase of force relaxation in both twitch and tetanus, but exhibited a secondary rise that closely coincided with the pseudoexponential fall of tension after the shoulder in the tetanus myogram. The rate of decay of [Ca2+]i during relaxation and the rate of decline of force both became progressively reduced by repetitive stimulation. 5. Stretch and shortening ramps performed during the plateau of an isometric tetanus had no detectable effect upon the calcium transient during the movement. By contrast, shortening and stretch imposed during the linear phase of relaxation both led to an increase of [Ca2+]i and to a steepening of the relaxation phase. 6. The results strongly suggest that the non-uniform length changes that are known to occur along a muscle fibre during relaxation enhance the release of calcium from the contractile system. The calcium mobilized in this way probably accounts for the transitory increase of [Ca2+]i that is observed during the latter part of force relaxation.
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PMID:Variation in myoplasmic Ca2+ concentration during contraction and relaxation studied by the indicator fluo-3 in frog muscle fibres. 796 29


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