Intracellular calcium (Ca2+) is an essential second messenger in eukaryotic cells regulating numerous cellular functions such as contraction, secretion, immunity, growth, and metabolism. Ca2+ signaling is also a key signal transducer in the intrinsic apoptosis pathway. The store-operated Ca2+ entry pathway (SOCE) is ubiquitously expressed in eukaryotic cells, and is the primary Ca2+ influx pathway in non-excitable cells. SOCE is mediated by the endoplasmic reticulum Ca2+ sensing STIM proteins, and the plasma membrane Ca2+-selective Orai channels. A growing number of studies have implicated SOCE in regulating cell death primarily via the intrinsic apoptotic pathway in a variety of tissues and in response to physiological stressors such as traumatic brain injury, ischemia reperfusion injury, sepsis, and alcohol toxicity. Notably, the literature points to excessive cytosolic Ca2+ influx through SOCE in vulnerable cells as a key factor tipping the balance towards cellular apoptosis. While the literature primarily addresses the functions of STIM1 and Orai1, STIM2, Orai2 and Orai3 are also emerging as potential regulators of cell death. Here, we review the functions of STIM and Orai proteins in regulating cell death and the implications of this regulation to human pathologies.

A tight control of intracellular [Ca[Formula: see text]] is essential for the survival and normal function of cells. In this study we investigate key mechanistic steps by which calcium is regulated and calcium oscillations could occur using in silico modeling of membrane transporters. To do so we give a deterministic description of intracellular Ca[Formula: see text] dynamics using nonlinear dynamics in order to understand Ca[Formula: see text] signaling. We first present the ordinary differential equations (ODEs) system for cell calcium kinetics and make a preliminary work on Sobol indices. We then describe and analyze complex transporters action. Besides, we analyze the whole system. We finally perform numerical simulations and compare our results to real data.

Activation of resting T cells relies on sustained Ca2+ influx across the plasma membrane, which in turn depends on the functional expression of potassium channels, whose activity repolarizes the membrane potential. Depending on the T-cells subset, upon activation the expression of Ca2+- or voltage-activated K+ channels, KCa or Kv, is up-regulated. In this study, by means of patch-clamp technique in the whole cell mode, we have studied in detail the characteristics of Kv and KCa currents in resting and activated human T cells, the only well explored human T-leukemic cell line Jurkat, and two additional human leukemic T cell lines, CEM and MOLT-3. Voltage dependence of activation and inactivation of Kv1.3 current were shifted up to by 15 mV to more negative potentials upon a prolonged incubation in the whole cell mode and displayed little difference at a stable state in all cell lines but CEM, where the activation curve was biphasic, with a high and low potential components. In Jurkat, KCa currents were dominated by apamine-sensitive KCa2.2 channels, whereas only KCa3.1 current was detected in healthy T and leukemic CEM and MOLT-3 cells. Despite a high proliferation potential of Jurkat cells, Kv and KCa currents were unexpectedly small, more than 10-fold lesser as compared to activated healthy human T cells, CEM and MOLT-3, which displayed characteristic Kv1.3high:KCa3.1high phenotype. Our results suggest that Jurkat cells represent perhaps a singular case and call for more extensive studies on primary leukemic T cell lines as well as a verification of the therapeutic potential of specific KCa3.1 blockers to combat acute lymphoblastic T leukemias.

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BACKGROUND: Repeated oscillations in intracellular calcium (Ca2+) concentration, known as Ca2+ spiking signals, have been described in plants for a limited number of cellular responses to biotic or abiotic stimuli and most notably the common symbiotic signaling pathway (CSSP) which mediates the recognition by their plant hosts of two endosymbiotic microbes, arbuscular mycorrhizal (AM) fungi and nitrogen fixing rhizobia. The detailed analysis of the complexity and variability of the Ca2+ spiking patterns which have been revealed in recent studies requires both extensive datasets and sophisticated statistical tools.
RESULTS: As a contribution, we have developed automated Ca2+ spiking analysis (CaSA) software that performs i) automated peak detection, ii) statistical analyses based on the detected peaks, iii) autocorrelation analysis of peak-to-peak intervals to highlight major traits in the spiking pattern.We have evaluated CaSA in two experimental studies. In the first, CaSA highlighted unpredicted differences in the spiking patterns induced in Medicago truncatula root epidermal cells by exudates of the AM fungus Gigaspora margarita as a function of the phosphate concentration in the growth medium of both host and fungus. In the second study we compared the spiking patterns triggered by either AM fungal or rhizobial symbiotic signals. CaSA revealed the existence of different patterns in signal periodicity, which are thought to contribute to the so-called Ca2+ signature.
CONCLUSIONS: We therefore propose CaSA as a useful tool for characterizing oscillatory biological phenomena such as Ca2+ spiking.

Mitochondria are key organelles involved in many aspects of plant physiology and, their ability to generate specific Ca²⁺ signatures in response to abiotic and biotic stimuli has been reported as one of their roles. The recent identification of the mammalian mitochondrial Ca²⁺ uniporter opens a new research area in plant biology. To study the mitochondrial Ca²⁺ handling, it is essential to have a reliable probe. Here we have reported the generation of an Arabidopsis transgenic line expressing the genetically encoded probe Cameleon D3cpv targeted to mitochondria, and compared its properties with the already known Cameleon YC3.6.

We examined the relationship between somatic Ca²⁺ signals and spiking activity of cerebellar molecular layer interneurons (MLIs) in adult mice. Using two-photon microscopy in conjunction with cell-attached recordings in slices, we show that in tonically firing MLIs loaded with high-affinity Ca²⁺ probes, Ca²⁺-dependent fluorescence transients are absent. Spike-triggered averages of fluorescence traces for MLIs spiking at low rates revealed that the fluorescence change associated with an action potential is small (1% of the basal fluorescence). To uncover the relationship between intracellular Ca²⁺ concentration ([Ca²⁺](i)) and firing rates, spikes were transiently silenced with puffs of the GABA(A) receptor agonist muscimol. [Ca²⁺](i) relaxed toward basal levels following a single exponential whose amplitude correlated to the preceding spike frequency. The relaxation time constant was slow (2.5 s) and independent of the probe concentration. Data from parvalbumin (PV)-/- animals indicate that PV controls the amplitude and decay time of spike-triggered averages as well as the time course of [Ca²⁺](i) relaxations following spike silencing. The [Ca²⁺](i) signals were sensitive to the L-type Ca²⁺ channel blocker nimodipine and insensitive to ryanodine. In anesthetized mice, as in slices, fluorescence traces from most MLIs did not show spontaneous transients. They nonetheless responded to muscimol iontophoresis with relaxations similar to those obtained in vitro, suggesting a state of tonic firing with estimated spiking rates ranging from 2 to 30 Hz. Altogether, the [Ca²⁺](i) signal appears to reflect the integral of the spiking activity in MLIs. We propose that the muscimol silencing strategy can be extended to other tonically spiking neurons with similar [Ca²⁺](i) homeostasis.

OBJECTIVE: The aim of this study was to demonstrate the feasibility of using samples obtained through muscle biopsy to assess a wide range of cellular properties, some of which may be abnormal in myalgia. Given the recent emphasis on the role of excitation-contraction coupling in health and disease, special emphasis is given to the characterization of the properties involved in this process.
METHODS: Tissue samples were obtained from the upper portion of the descending trapezius muscle in three female patients (PAT) with clinically diagnosed myalgia and assessed for a spectrum of properties related to substrate use, energy production, and excitation-contraction coupling and were compared with samples from three healthy controls.
RESULTS: At the level of organization of the metabolic pathways, all PAT generally displayed normal activities of enzymes representing the potential for oxidative phosphorylation, glucose phosphorylation, glycolysis, and lactate oxidation. In contrast, a reduced potential was observed in PAT for both fat oxidation (-20%) and high-energy phosphate transfer (-38%). For excitation-contraction coupling, PAT had a compromised sarcoplasmic reticulum maximal Ca-ATPase activity (-21%), Ca uptake (-44%), and sarcoplasmic endopleasmic reticulum (SERCA) expression for both SERCA1a (-16%) and SERCA2a (-17%), which were accompanied by a lower phase 2 Ca release (-45%). The Na-K-ATPase concentration, the enzyme-regulating membrane excitability via active Na and K seemed elevated (+25%) in PAT.
CONCLUSIONS: These results demonstrate the feasibility of analyzing tissue samples for a wide range of properties and provide a rationale for studies examining the cellular basis of myalgia with particular emphasis on sarcoplasmic reticulum Ca cycling, given the latter\'s role in regulating a wide range of cellular functions.

Changes in the orientation of tropomyosin on actin are important for the regulation of striated muscle contraction and could also be important for smooth muscle regulation. We showed earlier that acrylodan-labeled skeletal muscle tropomyosin reports the kinetics of the reversible transitions among the active, intermediate, and inactive states when S1 is rapidly detached from actin-tropomyosin. We now show that acrylodan-labeled smooth muscle tropomyosin reports similar transitions among states of actin-tropomyosin. When S1 was rapidly detached from actin-smooth muscle tropomyosin, there was a rapid decrease in acrylodan-tropomyosin fluorescence as the intermediate state became populated. The rate constant for this process was >600 s(-1) at temperatures near 5 °C. In the presence of skeletal troponin and EGTA, the decrease in fluorescence was followed by the redevelopment of fluorescence as the inactive state became populated. The apparent rate constant for the fluorescence increase was 14 s(-1) at 5 °C. Substituting smooth muscle caldesmon for skeletal muscle troponin produced a similar decrease and re-increase in fluorescence, but the apparent rate constant for the increase was >10 times that observed with troponin. Furthermore, the fluorescence increase was correlated with an increase in the extent of caldesmon attachment as S1-ATP dissociated. Although the measured rate constant appeared to reflect the rate-limiting transition for inactivation, it is unclear if the fluorescence change resulted from caldesmon binding, the movement of tropomyosin over actin, or both.

Neuronal calcium sensor-1 (NCS-1) is a Ca(2+) sensor protein that has been implicated in the regulation of various aspects of neuronal development and neurotransmission. It exerts its effects through interactions with a range of target proteins one of which is interleukin receptor accessory protein like-1 (IL1RAPL1) protein. Mutations in IL1RAPL1 have recently been associated with autism spectrum disorders and a missense mutation (R102Q) on NCS-1 has been found in one individual with autism. We have examined the effect of this mutation on the structure and function of NCS-1. From use of NMR spectroscopy, it appeared that the R102Q affected the structure of the protein particularly with an increase in the extent of conformational exchange in the C-terminus of the protein. Despite this change NCS-1(R102Q) did not show changes in its affinity for Ca(2+) or binding to IL1RAPL1 and its intracellular localisation was unaffected. Assessment of NCS-1 dynamics indicated that it could rapidly cycle between cytosolic and membrane pools and that the cycling onto the plasma membrane was specifically changed in NCS-1(R102Q) with the loss of a Ca(2+) -dependent component. From these data we speculate that impairment of the normal cycling of NCS-1 by the R102Q mutation could have subtle effects on neuronal signalling and physiology in the developing and adult brain.