Characteristics of store-operated calcium channels activated by depletion of the endoplasmic reticulum ryanodine-sensitive calcium stores in rat dorsal root ganglion neurons

In neurons of the rat dorsal root ganglia (DRG), using a patch-clamp technique in the whole-cell configuration, we studied the characteristics of calcium channels activated by depletion of the ryanodine-sensitive calcium stores of the endoplasmic reticulum. Current-voltage (I-V) relationships of these store-operated calcium channels were obtained by subtraction of the integral I-V characteristics after application of caffeine from the integral I-V characteristics of calcium channels in the control. Currents through store-operated calcium channels could be induced by application of a series of hyperpolarization current pulses to the cell under conditions of replacement of a calcium-free solution containing caffeine by a caffeine-free solution containing 2 mM Ca²⁺. In this case, the following two main conditions were abserved: Voltage-operated calcium channels were inactivated, while a gradient of the electrochemical potential for calcium ions was increased, which made easier passing of these currents through store-operated calcium channels. Therefore, we found that in DRG neurons, despite the presence of great numbers of both voltage-operated and receptor-dependent calcium channels, one more mechanism underlying the entry of calcium through store-operated channels does exist. Neirofiziologiya/Neurophysiology, Vol. 39, No. 3, pp. 195–200, May–June, 2007.     

Key role of calcium signaling in synaptic transmission

The review analyzes current concepts on the role of calcium signals in the process of synaptic neuron-to-neuron and neuron-effector transmission and on the respective intracellular mechanisms (participation of different types of ion channels, mitochondria, and endoplasmic reticulum). The involvement of calcium both in the transmission per se, in particular in the process of exocytotic neurotransmitter release, and in long-lasting modulations of the efficacy of synaptic transmission (potentiation or depression) is considered. Neirofiziologiya/Neurophysiology, Vol. 39, Nos. 4/5, pp. 290–293, July–October, 2007.     

Effects of Gabapentin on Calcium Transients in Neurons of the Rat Dorsal Root Ganglia

In our experiments on rat dorsal root ganglia (DRG) neurons, we studied the effects of an antiepileptic agent, gabapentin, on calcium transients evoked by depolarization of the membrane using the fluorescence calciumsensitive dye Fura-2/AM. Application of gabapentin to neurons with large-diameter somata practically did not change the characteristics of calcium transients. In mid-sized neurons, the amplitude of transients decreased, on average, by 27% with respect to the control, while in small-sized neurons the transients changed insignificantly (on average, less than by 7%). The mid-sized neurons were additionally subjected to the capsaicin test, which allowed us to differentiate primary nociceptive neurons of this group where TRPV1-type channels are expressed. In capsaicin-sensitive neurons, application of gabapentin led to a decrease in the amplitude of calcium transients, on average, by 37%, while such a decrease was only 16% in capsaicininsensitive neurons. Based on our own data and findings of other researchers on the ability of gabapentin to demonstrate affine binding with the accessory α₂δ subunit of voltage-dependent calcium channels and also on the peculiarities of expression of these channels in somatosensory neurons of the corresponding types, we discuss the probable pattern of expression of subunits of the α₂δ-1 subtype in DRG cells of different sizes. We demonstrated that the effects of gabapentin on calcium transients in nociceptive and hypothetically nonnociceptive mid-sized DRG neurons are selective (the effects in neurons involved in the sensation of acute pain are probably more intense). Neirofiziologiya/Neurophysiology, Vol. 40, No. 4, pp. 281–287, July–August, 2008.     

Dynamics of calcium release and uptake by the internal calcium stores in rat sensory neurons

Calcium dynamics in the endoplasmic reticulum of dorsal root ganglion neurons of rats during Ca²⁺ release induced by caffeine and subsequent Ca²⁺ uptake were studied. Calcium release is shown to include two (a short transient and a prolonged slow) phases. We suggest that the transient phase reflects release of free Ca from the calcium store, while the slow phase reflects transition of Ca from a bound form to a free one. The process of Ca²⁺ uptake is characterized by exponential recovery of the calcium level in the store due to the SERCA activity. Neirofiziologiya/Neurophysiology, Vol. 38, No. 4, pp. 361–363, July–August, 2006.     

Calpain as one of the calcium signal mediators in the cell

This review gathers together the available information on the structural and functional properties of an intracellular calcium-dependent protease, calpain, and its inhibitors and activators. Changes in the ideas about the mechanism of enzyme activation, its interaction with substrate, and regulation of functions are considered in light of recently obtained information. The multi-faceted participation of calpain in the realization of one of the most important physiological function connected with calcium signalization is demonstrated with concrete example (in particular, in the case of a memory model, based on long-term synaptic potentiation). Neirofiziologiya/Neurophysiology, Vol. 32, No. 2, pp. 142–156, March–April, 2000.     

Calcium Channels in the Nuclear Envelope of Pyramidal Neurons of the Rat Hippocampus

As is known, an increase in the concentration of Са²⁺ in the nuclei of nerve cells leads to activation of genes responsible for the formation of long-lasting postsynaptic changes; mechanisms of memory and learning are based on such changes. The pathways necessary for the entry of calcium into the nuclei of hippocampal pyramidal neurons remained unstudied. Using a patch-clamp technique, we studied what types of calcium channels exist in the membranes of isolated nuclei of pyramidal neurons of the hippocampal СА1 area. In the inner nuclear membrane of these cells, we, for the first time, found inositol trisphosphate receptors (IP₃Rs) activated by inositol trisphosphate applied in the concentration of ≥0.1 μM. The conductivity of single channels of such receptors was, on average, 366 pS; these channels were permeable for both monovalent and bivalent cations. Our data indicate that the nuclear envelope of pyramidal neurons of the hippocampal СА1 area can play the role of the calcium store from which Са²⁺ enter the cell nucleus directly. Neirofiziologiya/Neurophysiology, Vol. 40, No. 4, pp. 288–292, July–August, 2008.     

Changes in the intracellular calcium concentration upon activation of rat superior cervical ganglion neurons

Changes in the intracellular calcium concentration induced by activation of neurons of the isolated intact rat superior cervical ganglion were recorded. It is concluded that stimulation within the physiological range of frequencies can effectively increase the intracellular calcium concentration in these neurons. Neirofiziologiya/Neurophysiology, Vol. 39, Nos. 4/5, pp. 400–402, July–October, 2007.     

β-amyloid-induced changes in calcium homeostasis in cultured hippocampal neurons of the rat

A two-wave technique of calciometry with the use of a fluorescence dye, fura-2/AM, was applied for examination of the effect of a protein, β-amyloid (the main component of senile plaques in Alzheimer’s disease), on calcium homeostasis in cultured neurons of the rat hippocampus; β-amyloid was added to the culture medium. In most neurons, the effect of β-amyloid appeared as a more than twofold increase in the basic calcium concentration, as compared with the control (153.4 ± 11.5 and 71.7 ± 5.4 nM, respectively; P < 0.05). The characteristics of calcium transients induced by application of hyperpotassium solution also changed; the amplitude of these transients decreased, and the duration of a part corresponding to calcium release from the cell (rundown of the transient) increased. The mean amplitude of calcium transients under control conditions was 447.5 ± 20.1 nM, while after incubation in the presence of β-amyloid this index dropped to 278.4 ± 22.6 nM. Under control conditions, the decline phase of calcium transients lasted, on average, 100 ± 6 sec, while after incubation of hippocampal cell cultures in the presence of β-amyloid this phase lasted 250 ± 10 sec. Therefore, an excess of β-amyloid influences significantly calcium homeostasis in the nerve cells by disturbing functions of the calcium-controlling systems, such as voltage-operated calcium channels of the plasma membrane and calcium stores of the mitochondria and endoplasmic reticulum. Neirofiziologiya/Neurophysiology, Vol. 40, No. 1, pp. 9–12, January–February, 2008.     

Inhibition of a slowly inactivating high-voltage-activated calcium current by the neuropeptide FMRFa in molluscan neuroendocrine cells

Using the whole-cell voltage-clamp technique, the effects of the neuropeptide Phe-Met-Arg-Phe-NH₂ (FMRFa) on two types of dihydropyridine-sensitive, high-voltage-activated calcium currents were investigated in isolated neuroendocrine caudo-dorsal cells (CDCs), which control egg-laying in the molluscLymnaea stagnalis. These currents are: (1) a transient current (Τ_inact = ∼10–25 ms) with an activation threshold of −40 mV and maximal amplitude at +10 mV and (2) a sustained current (Τ_inact = ∼ 100–300 ms) with a threshold of −10 mV and apeak at +30 mV. FMRFa caused a partial block of the calcium current that was rapid, reversible and dose-dependent (ED₅₀ = 4.3 nM). The FMRFa-sensitive and insensitive currents differed in voltage-dependence of activation and inactivation, steady-state inactivation characteristics and time course of recovery from inactivation, all indicating that FMRFa selectively suppressed the sustained calcium current. Internal perfusion of CDCs with GTP-γ-S or GDP-Β-S depressed the FMRFa response, suggesting the involvement of G-proteins. Experiments aimed at elucidation of the signal transduction pathway between the FMRFa receptor and the calcium channel revealed no involvement of second messengers and protein kinases. The FMRFa-induced inhibition of the sustained calcium current probably results from a direct interaction between a G-protein, activated by the FMRFa receptor, and the calcium channel. The selective inhibition of this calcium current is likely to decrease the influx of calcium during the action potential, which will reduce the release of autoexcitatory CDC-peptides and contribute to a suppression of excitability.     

Individual and combined effects of calciotropic hormones and growth factors on mineral metabolism in embryonic chick tibiae

Summary We have investigated single and combined effects of calciotropic hormones and growth factors on the regulation of alkaline phosphatase (ALP) activity and calcium metabolism in an optimized serum-free bone organ culture system of embryonic chick tibiae. Parathyroid hormone PTH(1–34) alone mobilized calcium from bone tissue time- and dose-dependently and inhibited ALP activity. Both the bisphosphonate (BM 21.0955) and to a lesser extent salmon calcitonin alone slightly increased calcium uptake and inhibited the stimulation of bone resorption by PTH(1–34). 1,25(OH)₂D₃ mobilized calcium and inhibited ALP activity in contrast to 24,25(OH)₂D₃ which inhibited ALP activity but had no significant effect on calcium metabolism. Interestingly the combination of PTH(1–34) with 1,25(OH)₂D₃ but not 24,25(OH)₂D₃ reduced calcium mobilization. The combination of the midregional fragment PTH(28–48), which by itself has no effect on calcium metabolism, with 1,25(OH)₂D₃ reduced calcium mobilization more efficiently. Several PTH-regulated mediators have been assayed in this system. Of the tested growth factors, IGF-I at high concentrations caused bone resorption with no effect on ALP activity. TGF-β₁ (transforming growth factor β) and BMP-2 had no significant effect on calcium metabolism; however, ALP activity was inhibited by TGF-β₁ and induced dose dependently by BMP-2. Of the other factors known to be present in bone, platelet-derived growth factor (PDGF_A/B) and epidermal growth factor (EGF) had a small effect on calcium mobilization but had no effect on ALP activity. bFGF reduced ALP activity slightly without an effect on calcium metabolism. Our results show that this in vitro system can mimic some interactions of calciotropic hormones in vivo and allows the assaying of mediators in terms of regulation of ALP activity and of calcium metabolism.     

Rhythmic Activity of Murine Neuromuscular Junctions upon Activation of Release of Stored Calcium in the Presence of a Calcium Buffer

Using a two-electrode voltage-clamp technique, we recorded end-plate currents (EPCs) in neuromuscular synaptic junctions of the murine diaphragm upon rhythmic stimulation of the n. phrenicus with frequencies of 7, 20, 50, 70, and 100 sec⁻¹. Parameters of EPC series were analyzed against the background of the action of a mobilizer of intracellular calcium, ryanodine (0.5 μM), after the loading of terminals by 1.2 mM BAPTA (calcium buffer with rapid dynamics of binding of calcium), and upon the action of ryanodine in the presence of BAPTA. Under the action of ryanodine, the amplitude and quantum content of EPC within the plateau phase increased by 100 to 150% (P < 0.05). Loading with BAPTA evoked sharp decreases in the quantum content of unitary EPCs, the intensity of the initial facilitation, and the level of the EPC plateau in series within the entire range of stimulation frequencies used. Against the background of the action of BAPTA, the facilitatory effect of ryanodine increased; inhibitory effects of BAPTA with respect to the amplitude of unitary EPC and the level of the initial facilitation were completely compensated, whereas the level of EPC at the plateau stage increased to levels exceeding the control values by 50 to 70%. The ability of ryanodine to facilitate the transmitter (acetylcholine) release, which was enhanced in the presence of BAPTA, was completely neutralized by a blocker of L-type calcium channels, verapamil (5 μM). In the absence of BAPTA, verapamil did not influence the effects of ryanodine. We hypothesize that in the presence of BAPTA calcium channels of L type whose activity is resistive to the buffer action of BAPTA are disinhibited. The calcium current through L-type channels, perhaps, is capable of stimulating calcium release from the stores of nerve terminals and, as a consequence, of intensifying the facilitatory effect of ryanodine on the release of acetylcholine. After verapamil-induced blockade of this current, BAPTA demonstrates the ability to prevent the facilitatory effect of ryanodine on the transmitter release. Neirofiziologiya/Neurophysiology, Vol. 37, No. 4, pp. 330–338, July–August, 2005.     

Involvement of L-type calcium channels and mitochondria in post-tetanic potentiation: Is it a general rule for different types of synapses?

Our experiments and studies of a few other authors demonstrated that L-type calcium channels and mitochondria are involved in the induction of post-tetanic potentiation (PTP) in a number of preparations (Aplysia central nervous system, hippocampal cell cultures, crayfish neuromuscular junctions, etc.). We extend this conclusion on cortical synapses by the demonstration that inhibitors of mitochondrial Ca²⁺ uptake and release suppress PTP in rat neocortical cell cultures. Neirofiziologiya/Neurophysiology, Vol. 39, Nos. 4/5, pp. 403–404, July–October, 2007.     

Distribution of lead in human milk fractions

The purpose of this study was to determine the concentration and distribution of lead, calcium, iron, zinc, and copper in major fractions (fat, casein, whey) of mature milk from 38 nursing adult women with low environmental lead exposure. The potential associations between milk lead and maternal blood lead and between milk and blood lead and essential mineral data (nutritional status, dietary intake, and milk concentration) were investigated. Maternal blood lead (geometric mean, 60 μg/L) was negatively associated, although modestly, with dietary calcium intake (r=−0.32, p=0.02). Lead in whole milk (geometric mean, 1.2 μg/L) was positively associated with calcium in whole milk (r=0.56, p=0.005). Distribution of lead in milk fractions was 63%, 28%, and 9%, in whey, fat, and casein, respectively. Milk distribution of essential minerals was 67–76%, 17–18%, and 7–17% in whey, fat, and casein, respectively. Lead in milk whey was positively associated with lead in maternal blood (r=0.49, p=0.02). However, milk lead was not affected by nutritional status, dietary intake, and milk composition of the essential minerals. The high percentage of lead in the milk whey fraction, as seen for the essential minerals, suggests that most lead in human milk is bioavailable to the infant.     

Calmodulin’s flexibility allows for promiscuity in its interactions with target proteins and peptides

The small bilobal calcium regulatory protein calmodulin (CaM) activates numerous target enzymes in response to transient changes in intracellular calcium concentrations. Binding of calcium to the two helix-loop-helix calcium-binding motifs in each of the globular domains induces conformational changes that expose a methionine-rich hydrophobic patch on the surface of each domain of the protein, which it uses to bind to peptide sequences in its target enzymes. Although these CaM-binding domains typically have little sequence identity, the positions of several bulky hydrophobic residues are often conserved, allowing for classification of CaM-binding domains into recognition motifs, such as the 1–14 and 1–10 motifs. For calcium-independent binding of CaM, a third motif known as the IQ motif is also common. Many CaM-peptide complexes have globular conformations, where CaM’s central linker connecting the two domains unwinds, allowing the protein to wrap around a single predominantly α-helical target peptide sequence. However, novel structures have recently been reported where the conformation of CaM is highly dissimilar to these globular complexes, in some instances with less than a full compliment of bound calcium ions, as well as novel stoichiometries. Furthermore, many divergent CaM isoforms from yeast and plant species have been discovered with unique calcium-binding and enzymatic activation characteristics compared to the single CaM isoform found in mammals.     

Mackerel from the northern indian ocean and the red sea arescomber australasicus, notscomber japonicus

The population ofScomber from the Red Sea and northern Indian Ocean (gulfs of Aden and Oman) is identified asS. australasicus rather thanS. japonicus based on having 30–33 vs. 26–29 interneural bones under the first and second dorsal fins and the combination of interneural bone counts of 16–20 under the first dorsal fin (vs. 13–16) and first dorsal fin spine counts of 10–13 (vs. 9–10). These are the best morphological characters to distinguish these two species. This change in identification constitutes a major range extension forS. australasicus which was thought to be restricted to the Pacific Ocean and the southeastern Indian Ocean around Western Australia.     

Niphon spinosus,a primitive Epinepheline serranid: Corroborative evidence from the larvae

The larvae ofNiphon spinosus are described based on seven specimens (4.2 mmNL–7.2 mmSL) collected in the East China Sea during October and November of 1980–1984. The morphology of these larvae, in particular the elongate third dorsal spine and the configuration of the developing anterior dorsal pterygiophore complex, corroborates the hypothesis thatNiphon is a member of the serranid subfamily Epinephelinae. Within the Epinephelinae larvalNiphon resemble most closely those of the tribe Epinephelini, but differ in several respects, such as the absence of serrations on the dorsal, pelvic and preopercular spines. Using outgroup comparison as a basis for character polarization, a character analysis demonstrates that it is most parsimonious to hypothesize thatNiphon is the sister group of all other epinepheline tribes rather than the sister group of the tribe Epinephelini.     

Antagonism between olive oil phenolics and nitric oxide on lymphomonocyte cytosolic calcium

Some biological actions of olive oil phenolics (inhibition of platelet aggregation, decrease of LDL-oxidation, inhibition of bacterial growth and hypertensive action) have been attributed to NOS stimulation in endothelial cells through an increase of cytosolic calcium, notwithstanding the scavenging activity of phenolics on NO and superoxide. In this paper, we determine the concentration of cytosolic calcium in human lymphomonocytes incubated with high concentrations of NO-donors (CysNO) and we evaluate the effects of olive oil phenolics on this parameter. CysNO induces a marked decrease of cytosolic calcium; both olive oil phenolics oppose this action of CysNO. The effects of phenolics and CysNO are independent and additive. (Mol Cell Biochem xxx: 181–184, 2005)     

The Effect of Nimodipine on Calcium Homeostasis and Pain Sensitivity in Diabetic Rats

Summary 1. The pathogenesis of diabetic neuropathy is a complex phenomenon, the mechanisms of which are not fully understood. Our previous studies have shown that the intracellular calcium signaling is impaired in primary and secondary nociceptive neurons in rats with streptozotocin (STZ)-induced diabetes. Here, we investigated the effect of prolonged treatment with the L-type calcium channel blocker nimodipine on diabetes-induced changes in neuronal calcium signaling and pain sensitivity.2. Diabetes was induced in young rats (21 p.d.) by a streptozotocin injection. After 3 weeks of diabetes development, the rats were treated with nimodipine for another 3 weeks. The effect of nimodipine treatment on calcium homeostasis in nociceptive dorsal root ganglion neurons (DRG) and substantia gelatinosa (SG) neurons of the spinal cord slices was examined with fluorescent imaging technique.3. Nimodipine treatment was not able to normalize elevated resting intracellular calcium ([Ca²⁺] _i ) levels in small DRG neurons. However, it was able to restore impaired Ca²⁺ release from the ER, induced by either activation of ryanodine receptors or by receptor-independent mechanism in both DRG and SG neurons.4. The beneficiary effects of nimodipine treatment on [Ca²⁺] _i signaling were paralleled with the reversal of diabetes-induced thermal hypoalgesia and normalization of the acute phase of the response to formalin injection. Nimodipine treatment was also able to shorten the duration of the tonic phase of formalin response to the control values.5. To separate vasodilating effect of nimodipine Biessels et al., (Brain Res. 1035:86–93) from its effect on neuronal Ca²⁺ channels, a group of STZ-diabetic rats was treated with vasodilator – enalapril. Enalapril treatment also have some beneficial effect on normalizing Ca²⁺ release from the ER, however, it was far less explicit than the normalizing effect of nimodipine. Effect of enalapril treatment on nociceptive behavioral responses was also much less pronounced. It partially reversed diabetes-induced thermal hypoalgesia, but did not change the characteristics of the response to formalin injection.6. The results of this study suggest that chronic nimodipine treatment may be effective in restoring diabetes-impaired neuronal calcium homeostasis as well as reduction of diabetes-induced thermal hypoalgesia and noxious stimuli responses. The nimodipine effect is mediated through a direct neuronal action combined with some vascular mechanism.     

Potassium permeability of voltage-operated calcium channels of dorsal root ganglion neurons in a calcium-free medium

In freshly isolated neurons of the rat spinal ganglia, we studied the behavior of voltage-operated calcium channels of these cells under conditions of the absence of calcium ions in the extracellular solution; a patch-clamp technique in the whole-cell configuration was used. We found that such channels in a part of the studied neurons lose their selectivity in a calcium-free potassium-containing solution and become capable of passing an inward potassium current. This current was inhibited by blockers of voltage-operated calcium channels, nifedipine and nickel, and also was to some extent inhibited by caffeine. The latter effect is realized, perhaps, due to calcium-dependent inactivation of calcium channels induced by the action of calcium ions released from the endoplasmic reticulum upon caffeine-induced activation of ryanodine receptors. The peculiarities of current-voltage relationships and characteristics of activation/inactivation of calcium channels modified in calcium-free medium and the possible mechanisms of such modification are discussed. Neirofiziologiya/Neurophysiology, Vol. 40, No. 2, pp. 93–99, March–April, 2008.