Biomedical subjects

K G Reymann

Publications and source records attributed to K G Reymann.

At least 37 records · Page 2Linked to original sources

PubMed1999

Protective effect of group I metabotropic glutamate receptor activation against hypoxic/hypoglycemic injury in rat hippocampal slices: timing and involvement of protein kinase C.

Excessive release of glutamate during ischemia leads to sustained neuronal damage. In this study we investigated the influence of metabotropic glutamate receptor (mGluR) activation on neuronal recovery from a hypoxic/hypoglycemic event in hippocampal slices from rats. The slices were transiently exposed to an oxygen- and glucose-free environment in an interface chamber and the synaptically evoked population spike in the CA1 region was taken as a measure of neuronal viability. Under control conditions the population spike amplitude recovered to 41.4% of baseline value within 1 h after hypoxia/hypoglycemia. The specific mGluR group I agonist 3,5-dihydroxyphenylglycine (DHPG, 10 microM) increased the recovery rate to 88.3% of baseline value when applied from 20 min before until 10 min after the event. Similar recovery rates were obtained when DHPG was present only 10 or 20 min before hypoxia/hypoglycemia (89.3% and 79.3% of baseline value, respectively). However, when applied later, DHPG had no protective effect. Co-application of the protein kinase C (PKC) inhibitors staurosporine (100 nM) or chelerythrine (30 microM) prevented the protective effect of DHPG. Our data suggest that group I mGluR agonists are only protective when present prior to the onset of the hypoxic/hypoglycemic event and that the activation of PKC is a critical step of the protective mechanism.

Alkaloids↗

PubMed1999

The novel Na+/Ca2+ exchange inhibitor KB-R7943 protects CA1 neurons in rat hippocampal slices against hypoxic/hypoglycemic injury.

The selective Na+/Ca2+ exchange inhibitor 2-[2-[4-(4-nitrobenzyloxy)phenyl]ethyl]isothiourea methanesulfonate (KB-R7943), significantly improves recovery of population spike amplitudes in rat hippocampal slices after hypoxia/hypoglycemia. Our data suggest that the Na+/Ca2+ exchanger, operating in reverse mode, contributes to hypoxia/hypoglycemia-induced injury in CA1 neurons.

Animals↗

PubMed1999

ACPD-mediated slow-onset potentiation is associated with cell death in the rat CA1 region in vivo.

Slow-onset potentiation of synaptic transmission in the hippocampus in vitro and in vivo is induced by application of the metabotropic glutamate receptor (mGluR) agonist, 1S,3R-amino cyclopentane 2,3-dicarboxylic acid (ACPD). This study investigated the cellular response in the CA1 region of freely moving rats to ACPD application. Drugs were applied via the lateral cerebral ventricle, and measurements were obtained from the CA1 region via permanently implanted electrodes. ACPD (20 nmol/5 microl) produced a dose-dependent slow-onset potentiation in the CA1 region which lasted over 4 h. Histological evaluation at either 4 h or 7 days following ACPD-injection indicated that slow-onset potentiation was associated with gradual but marked cell death in the CA1 region. Whereas 20 nmol ACPD produced significant CAI neurotoxicity, concentrations which did not induce potentiation had little or no neurotoxic effect. Both the general mGluR antagonist R,S-alpha-methyl-carboxyphenylglycine (1 micromol/5 microl), and the group 1 mGluR antagonist (S)-4-carboxyphenylglycine (4CPG, 100 nmol/5 microl) significantly inhibited ACPD-induced neuropathology. In addition, 4CPG inhibited the expression of ACPD-mediated slow-onset potentiation. These results confirm previous findings that in the CA1 region in vivo, slow-onset potentiation is mediated group 1 mGluRs, and indicate that slow-onset potentiation may involve pathological processes.

Animals↗

PubMed1999

Evidence for an ephaptic feedback in cortical synapses: postsynaptic hyperpolarization alters the number of response failures and quantal content.

The amplitude of excitatory postsynaptic potentials and currents increases with membrane potential hyperpolarization. This has been attributed to an increase in the driving force when the membrane potential deviates from the equilibrium potential of the respective ions. Here we report that in a subset of neocortical and hippocampal synapses, postsynaptic hyperpolarization affects traditional measures of transmitter release: the number of failures, coefficient of variation of response amplitudes, and quantal content, suggesting increased presynaptic release. The result is compatible with the hypothesis of Byzov on the existence of electrical (or "ephaptic") linking in purely chemical synapses. The linking, although negligible at neuromuscular junctions, could be functionally significant in influencing transmitter release at synapses with high resistance along the synaptic cleft. Our findings necessitate reconsideration of classical amplitude-voltage relations for such synapses. Thus, synaptic strength may be enhanced by hyperpolarization of the postsynaptic membrane potential. The positive ephaptic feedback could account for "all-or-none" excitatory postsynaptic potentials at some cortical synapses, large evoked and spontaneous multiquantal events and a high efficacy of large "perforated" synapses whose number increases following behavioural learning or the induction of long-term potentiation.

2-Amino-5-phosphonovalerate↗

PubMed1999

Presynaptic group 1 metabotropic glutamate receptors may contribute to the expression of long-term potentiation in the hippocampal CA1 region.

In this study, we investigated the possible contribution of presynaptic group 1 metabotropic glutamate receptor activation to changes in synaptic efficacy by means of analysis of glutamate release in hippocampal synaptosomes. Data were interpreted in the context of group 1 metabotropic glutamate receptor involvement in synaptic plasticity in the CA1 region of freely moving rats. In synaptosomes, 3,5-dihydroxyphenylglycine enhanced diacylglycerol formation and facilitated vesicular Ca(2+)-dependent glutamate release, whereas trans-azetidine-2,4-dicarboxylic acid had no effect on these processes. Trans-azetidine-2,4-dicarboxylic acid enhanced glutamate release, but in a Ca(2+)-independent manner. This effect was mimicked by the L-glutamate uptake inhibitor L-trans-pyrrolidine-2,4-dicarboxylic acid. (R,S)-alpha-Methyl-4-carboxyphenylglycine blocked the effects of 3,5-dihydroxyphenylglycine, but not trans-azetidine-2,4-dicarboxylic acid in synaptosomes. Short-term potentiation (100 Hz, three bursts of 10 stimuli, 0.1 ms stimulus duration, 10 s interburst interval) was induced in the CA1 region in vivo. The metabotropic glutamate receptor agonist 1S,3R-aminocyclopentane-2,3-dicarboxylic acid, or the group 1 metabotropic glutamate receptor agonists, 3,5-dihydroxyphenylglycine and trans-azetidine-2,4-dicarboxylic acid, dose-dependently facilitated short-term potentiation into long-term potentiation, which lasted > 24 h. The facilitation was inhibited by the metabotropic glutamate receptor antagonist, (R,S)-alpha-methyl-4-carboxyphenylglycine, and the group 1 metabotropic glutamate receptor antagonist, (S)-4-carboxy-phenylglycine, but not by the group 2 metabotropic glutamate receptor antagonist, (R,S)-alpha-methylserine-O-phosphate monophenyl ester. L-Trans-pyrrolidine-2,4-dicarboxylic acid dose-dependently facilitated short-term potentiation into long-term potentiation, which lasted < 4 h. These data suggest that activation of group 1 metabotropic glutamate receptors results in presynaptic modulation of glutamate release. This effect may contribute to group 1 metabotropic glutamate modulation of the expression of long-term potentiation in vivo.

Animals↗

PubMed1999

Time-dependent induction of depotentiation in the dentate gyrus of freely moving rats: involvement of group 2 metabotropic glutamate receptors.

Depotentiation comprises a reversal of tetanization-induced long-term potentiation (LTP) which occurs following low-frequency stimulation (LFS) in the hippocampus in vivo. Although depotentiation has been consistently demonstrated in the CA1 region, no positive reports of the existence of depotentiation in the dentate gyrus in vivo have occurred. This study therefore investigated whether depotentiation is possible in the dentate gyrus in vivo. We found that depotentiation can be induced, but it is very tightly dependent on the interval between tetanization and LFS. Thus, LFS given 2 or 5 min following tetanization produced significant depotentiation, whereas LFS given 10-30 min following tetanization had no significant effect on the expression of LTP. Depotentiation occurred in two phases: a transient depression of evoked responses to below pre-tetanization values, which occurred in the first 60 min following LFS, and a recovery of this response to a stable level of synaptic transmission which comprised a significant reduction in the magnitude of LTP. Group 2 metabotropic glutamate receptors (mGluRs) play an important role in the expression of long-term depression in vivo. We therefore investigated whether group 2 mGluRs contribute to depotentiation. The group 2 antagonist (2S)-alpha-ethylglutamic acid (EGLU) inhibited the early transient depression at a concentration which inhibits LTD in vivo, but did not block the expression of depotentiation. EGLU also inhibited the transient depression induced by 5 Hz given alone. Increasing the concentration of EGLU prevented depotentiation, however. The group 2 agonist (S)-4-carboxy-3-hydroxyphenyl- glycine (4C3HPG) inhibited LTP and enhanced depotentiation. These data suggest a role for group 2 mGluRs in depotentiation.

Animals↗

PubMed1998

Long-term potentiation in vivo increases rat hippocampal tenascin-C expression.

We investigated the expression of the extracellular matrix glycoprotein tenascin-C after induction of long-term potentiation (LTP) by high-frequency tetanization (HFT) in the rat dentate gyrus in vivo. Expression of tenascin-C was evaluated at the mRNA and protein levels by in situ hybridization and immunocytochemistry, respectively. Whereas no tenascin-C mRNA was detectable in control animals, an increase in tenascin-C mRNA levels was observed in the granule cell layer of the dentate gyrus 4 h after HFT. At 24 h after HFT, tenascin-C mRNA had returned to control levels. Expression of tenascin-C protein 4 h after HFT followed that of controls in that tenascin was detectable in the strata oriens and radiatum of CA1, in the molecular layer, and within a narrow area at the inner surface of the granule cell layer in the dentate gyrus. However, 24 h after HFT, additional patches of tenascin-C immunoreactivity were observed in the molecular layer of the dentate gyrus. No increase in tenascin mRNA or protein levels was detected in control animals that received no stimulation, low-frequency stimulation, or HFT in the presence of the N-methyl-D-aspartate receptor antagonist D(-)-2-amino-5-phosphonopentanoic acid or the metabotropic glutamate receptor antagonist (R,S)-alpha-methyl-4-carboxyphenylglycine. These observations implicate a role for tenascin-C in N-methyl-D-aspartate and metabotropic glutamate receptor-dependent changes accompanying induction and/or maintenance of LTP.

2-Amino-5-phosphonovalerate↗

PubMed1998

The role of group II metabotropic glutamate receptors in hippocampal CA1 long-term potentiation in vitro.

The role of group II metabotropic glutamate receptors (mGlu receptors) in mechanisms of long-term potentiation was investigated by analysis of excitatory postsynaptic field potentials of the CA1 region in rat hippocampal slices. The application of the group II agonists (2S,1'S,2'S)-2-(carboxycyclopropyl) glycine (L-CCG-I) and (2S,1'R,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl) glycine (DCG IV) resulted in a dose-dependent reduction of long term potentiation in the concentration range 3-50 microM. In contrast to the effects of group II agonists on long-term potentiation, the group II antagonists (RS)-alpha-methyl-3-carboxy-4-hydroxy-phenylglycine (M3C4HPG) and (RS)-alpha-methylserine-O-phosphate monophenyl ester (MSOPPE) elicited a dose-dependent enhancement of long-term potentiation (50-100 microM or 20-50 microM, respectively). We conclude that group II mGlu receptors are not essential for the induction of long-term potentiation; however, they may be involved in feedback mechanisms in long-term potentiation.

Amino Acids, Dicarboxylic↗

PubMed1998

Inhibition of apamin-sensitive calcium dependent potassium channels facilitate the induction of long-term potentiation in the CA1 region of rat hippocampus in vitro.

Using field potential recording in the CA1-region of rat hippocampal slices we investigated the effect of apamin; a specific antagonist of small conductive calcium activated potassium channels on long-term potentiation (LTP). The experiments revealed that LTP of excitatory postsynaptic potentials induced by a single 100 Hz tetanization was intensified by extracellular application of apamin in a concentration range of 1-200 nM. No effects of apamin on LTP induced by triple 100 Hz tetanization were seen. We conclude that the positive modulation of LTP by apamin is effective in a nanomolar concentration range and dependent upon the employed tetanization. Because it has been shown that apamin-binding sites are affected by learning disorders including Alzheimer's disease, our finding suggests that changes in the sensitivity to apamin may result in memory disorders.

Animals↗

PubMed1998

When are class I metabotropic glutamate receptors necessary for long-term potentiation?

The involvement of metabotropic glutamate receptors (mGluRs) in hippocampal long-term potentiation (LTP) is a matter of controversial debate. Using [Ca2+]i measurements by confocal laser scanning microscopy and field recordings of EPSPs (fEPSPs) in the hippocampal CA1-region, we found that the efficacy of the broad-spectrum mGluR-antagonist (S)-alpha-methyl-4-carboxyphenylglycine (MCPG) and of (S)-4-carboxy-phenylglycine (4-CPG), a selective antagonist at class I mGluRs, in LTP is contingent on the tetanization strength and the resulting [Ca2+]i response. As indicated by experiments in which we blocked voltage-dependent calcium channels (VDCCs) and intracellular Ca2+ stores (ICSs), the functional significance of class I mGluRs in LTP is confined to certain types of potentiation, which are induced by weak tetanization protocols and require the release of Ca2+ from ICSs for induction. During strong tetanic stimulation, this Ca2+ source is functionally bypassed by activating VDCCs.

Animals↗

PubMed1998

Semi-automated analysis of NMDA-mediated toxicity in digitised colour images from rat hippocampus.

The evaluation of neuronal cell survival after, for example, mechanical, hypoxic or drug-mediated injury requires the analysis of a high number of histological specimens. Since this is a time-consuming occupation, we have developed a semi-automated analysis routine for the determination of the distribution of live and dead cells. After digitalization of the histological preparations, 8-bit colour bitmaps were assessed using a compiled image-analysis programme of the software package Khoros. In the current study a detailed example of the application of this image-processing approach is described for the investigation of the cell survival after intraventricular application of N-methyl-D-aspartate (NMDA). The samples were prepared as fuchsin acid/toluidine blue stained hippocampal thin slices. The calculated areas of the live and dead cells were highly correlated with manual counts of live and dead cells in the 100 samples examined in this study. Twenty-four hours following NMDA-treatment animals (n = 5) were found to have significantly fewer live and more dead hippocampal cells than the saline-treated animals (n = 5), using either automated or manual examination techniques. The automated technique also revealed that NMDA treatment resulted in a reduction in the density of live cell distribution.

Animals↗

PubMed1998

The mGlu receptor ligand (S)-4C3HPG protects neurons after global ischaemia in gerbils.

(S)-4-Carboxy-3-hydroxy-phenylglycine [(S)-4C3HPG] is a potent competitive antagonist at the metabotropic glutamate receptor 1 subtype (mGlu1 receptor) and an agonist at mGlu2/3 receptor. We evaluated histologically the effect of this compound on transient global ischaemia in gerbils and observed pronounced neuroprotection in the CA1 layer of the hippocampus. When (S)-4C3HPG (1 microM) was administered intra-cerebroventricularly (i.c.v.) 20 min before clamping both common carotid arteries neuronal density was comparable with that in sham-operated animals. A single injection (1 microM) 65 min after ischaemia also significantly reduced neuronal damage. The results suggest that metabotropic glutamate receptors play a role in the deleterious cascade which leads to neuronal damage of pyramidal cells in the CA1 layer of the hippocampus after transient global ischaemia.

Animals↗

PubMed1998

Principal component analysis of minimal excitatory postsynaptic potentials.

'Minimal' excitatory postsynaptic potentials (EPSPs) are often recorded from central neurones, specifically for quantal analysis. However the EPSPs may emerge from activation of several fibres or transmission sites so that formal quantal analysis may give false results. Here we extended application of the principal component analysis (PCA) to minimal EPSPs. We tested a PCA algorithm and a new graphical 'alignment' procedure against both simulated data and hippocampal EPSPs. Minimal EPSPs were recorded before and up to 3.5 h following induction of long-term potentiation (LTP) in CA1 neurones. In 29 out of 45 EPSPs, two (N=22) or three (N=7) components were detected which differed in latencies, rise time (Trise) or both. The detected differences ranged from 0.6 to 7.8 ms for the latency and from 1.6-9 ms for Trise. Different components behaved differently following LTP induction. Cases were found when one component was potentiated immediately after tetanus whereas the other with a delay of 15-60 min. The immediately potentiated component could decline in 1-2 h so that the two components contributed differently into early (< 1 h) LTP1 and later (1-4 h) LTP2 phases. The noise deconvolution techniques was applied to both conventional EPSP amplitudes and scores of separate components. Cases are illustrated when quantal size (upsilon) estimated from the EPSP amplitudes increased whereas upsilon estimated from the component scores was stable during LTP1. Analysis of component scores could show apparent double-fold increases in upsilon which are interpreted as reflections of synchronized quantal releases. In general, the results demonstrate PCA applicability to separate EPSPs into different components and its usefulness for precise analysis of synaptic transmission.

Algorithms↗

PubMed1998

Pharmacological characterisation of metabotropic glutamatergic and purinergic receptors linked to Ca2+ signalling in hippocampal astrocytes.

Intracellular Ca2+ ([Ca2+]i) signals induced by metabotropic glutamate receptor (mGluR) agonists and by purinergic agonists in cultured hippocampal astrocytes were investigated using [Ca2+]-sensitive fluorophores. The mGluR agonists (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD) and (R,S)-3,5-dihydroxyphenylglycine (DHPG) induced [Ca2+]i responses in 76 and 93% of the cells, respectively. The broad-spectrum mGluR antagonist (+)-alpha-methyl-4-carboxyphenylglycine (MCPG) and the mGluR1 antagonists (S)-4-carboxy-3-hydroxyphenylglycine (4C3HPG) and (S)-4-carboxyphenylglycine (4CPG) suppressed the agonist-evoked [Ca2+]i response in about 25% of the cells completely and in about 60% partially, depending on the agonist concentration employed. Together with immunohistochemical receptor localisations these results suggest the presence of at least two subpopulations of class I mGluRs recruited from the truncated splice variants of mGluR1 (mGluR 1b, 1c, 1d) and/or hitherto unknown glial-specific class I mGluRs. Of the hippocampal astrocytes 88, 92 or 83% of the cells responded with a [Ca2+]i elevation (mostly oscillations) to application of ATP, ADP, or 2-methylthio-ATP (2-MeS-ATP), respectively, whereas only 14 and 5% responded to AMP and adenosine, respectively, indicating the predominance of P2 receptors. The ATP-induced [Ca2+]i signal was suppressed by suramin. Release of Ca2+ from intracellular stores was involved in the response to ATP because the cells also exhibited [Ca2+]i elevations in Ca2+-free medium. Cells did not respond to 10 microM UTP. We conclude that the P2Y subtype represents the main [Ca2+]i-linked purinoceptor in hippocampal astrocytes. Sequential application of ATP and DHPG in Ca-free medium showed that metabotropic glutamate and purinergic receptors initiate release of Ca2+ from subsets of cyclopiazonic acid-sensitive Ca2+ stores which are partly independent.

Adenosine↗

PubMed1998

(S)-4C3HPG reduces infarct size after focal cerebral ischemia.

This study investigated whether the metabotropic glutamate receptor ligand (S)-4C3HPG can reduce brain damage after focal ischemia in rats. Application of 1 micromol of (S)-4C3HPG (intracerebroventricularly) 5 min after occlusion of the middle cerebral artery significantly reduced the infarct size by 72.3% of the saline control.

Animals↗

PubMed1998

In vivo electrophysiological investigations into the role of histamine in the dentate gyrus of the rat.

Drugs acting at the three known classes of histamine receptors were injected intracerebroventricularly into the rat. The effects of these drugs upon synaptic potentials recorded from the dentate gyrus of the freely-moving rat were determined. Population spikes and field excitatory postsynaptic potentials were recorded from the granule cell layer of the dentate gyrus following stimulation of the perforant path. Drugs, dissolved in 0.9% NaCl were applied into the lateral cerebral ventricle in a volume of 5 microl over a period of 6 min. The histamine H1 receptor antagonist mepyramine (0.4 or 0.8 microg) had no significant effect on population spikes or field excitatory postsynaptic potentials. In contrast the H2 receptor antagonist cimetidine (3.25, 6.5 or 13 microg) showed a biphasic effect. At the lower doses (3.25 or 6.5 microg) a small (15%) depression of the field excitatory postsynaptic potentials and population spikes was observed beginning about 1 h following the infusion. At the highest dose tested (13 microg) a marked increase of the population spike was observed beginning immediately following the infusion and lasting for 90 min. Application of the H3 receptor agonist R-alpha-methylhistamine (0.2 microg) depressed the field excitatory postsynaptic potentials (15% at 4 h post-injection) and even more strongly the population spike (50%). Surprisingly, at higher doses (0.4 and 0.8 microg) no effect was seen. The H3 receptor antagonist thioperamide (0.41 and 0.82 microg) did not cause an increase in synaptic potentials but rather at the highest dose a small depression occurred at later time points (2-4 h following the infusion). At the lower dose (0.41 microg) thioperamide blocked the effect of R-alpha-methylhistamine (0.2 microg). These results show that the histaminergic system modulates information flow through the dentate gyrus in a complex manner involving both histamine H2 and H1 receptors.

Animals↗

PubMed1998

Interaction between paired-pulse facilitation and long-term potentiation of minimal excitatory postsynaptic potentials in rat hippocampal slices: a patch-clamp study.

Long-term potentiation is an experimental paradigm used to study synaptic plasticity and memory mechanisms. One similarity between long-term potentiation and memory is the existence of several distinct phases. However, our preliminary quantal analysis did not reveal essential differences in expression mechanisms of the early (< 1 h) and later (up to 3 h) phases of long-term potentiation. The data were compatible with presynaptic mechanisms of both phases. Another approach to distinguish between presynaptic and postsynaptic mechanisms is analysis of interaction between long-term potentiation and presynaptic paired-pulse facilitation. Such analysis had been previously done mainly with recordings of field potentials reflecting the activity of large neuronal populations. Only the early potentiation phase had been previously analysed with recordings from single neurons. The results from different groups were contradictory. In the present study, minimal excitatory postsynaptic potentials were recorded from CA1 pyramidal neurons of rat hippocampal slices. Paired-pulse facilitation ratios were calculated for various periods (up to 2-3 h) following induction of long-term potentiation. The ratio persistently decreased in the majority of neurons following long-term potentiation induction. The decrease in the paired-pulse facilitation ratio correlated with the magnitude of long-term potentiation and with the initial (pretetanic) facilitation ratio. Therefore, the general results of the present analysis was similar with the results of the quantal analysis: it is consistent with a strong involvement of presynaptic mechanisms in maintenance of both early and late phases of long-term potentiation. However, individual neurons could show variable changes in the paired-pulse facilitation, e.g., increases at late (> 0.5-1 h) periods after tetanus. Calculations of partial correlations and regression analysis indicated that positive correlation between potentiation magnitude and initial (pretetanic) paired-pulse facilitation tended to increase in the late potentiation phase (1.5-2.5 h post-tetanus) indicating that different mechanisms are involved in the early (0.5 h post-tetanus) and the late phase of long-term potentiation. The findings are compatible with involvement of presynaptic mechanisms in both the early and late phases of long-term potentiation. However, the results suggest that contribution of changes in release probability and in effective number of transmitter release sites may differ during the two phases. It is suggested that activation of silent synapses and increases in the number of transmission zones due to pre- and postsynaptic structural rearrangements represent important mechanisms of the late phase of long-term potentiation.

Animals↗

PubMed1998

Analysis of the tetanic and post-tetanic components of intradendritic Ca2+ signals in hippocampal CA1 neurons.

The importance of both the activation of second messenger cascades and an increase of the intracellular Ca2+ concentration for the induction of synaptic plasticity in hippocampal CA1 neurons is well established. Using the dye Calcium Green-1, we analysed the Ca2+ increases evoked by different 100-Hz tetanization paradigms commonly used to induce long-term potentiation. We found that the normalized total area of fluorescence intensity changes (F/F0) was correlated with both the strength and the duration of tetanization. Furthermore, the normalized area of fluorescence intensity changes during the time of tetanization (tetanic component) correlated strongly in a linear manner with the tetanization duration. Moreover, the tetanic component strongly determined the area of the post-tetanic Ca2+ signal. Interestingly, the normalized relationship of the post-tetanic Ca2+ signal to the total Ca2+ change decreased with prolonged tetanizations. In contrast, with an increased stimulation strength, a positive correlation of the relationship of the post-tetanic component to the total amount Ca2+ could be obtained. The time constants of the Ca2+ extrusion depend linearly on both the tetanization duration and the amount of the tetanic Ca2+ signal. Our data demonstrate that augmenting the stimulation strength leads to a respective increase of the post-tetanic Ca2+ portion within the total Ca2+ signal, whereas a prolongation of the tetanization duration does not. Thus, no further significant prolongation of the Ca2+ signal occurs during increased durations of tetanization.

Animals↗