Low temperature molecular adaptation of the skeletal muscle sarco(endo)plasmic reticulum Ca2+-ATPase 1 (SERCA 1) in the wood frog (Rana sylvatica)

Cooling of male rat skeletal muscle during endurance-like contraction attenuates contraction-induced PGC-1α mRNA expression

This study aimed to determine effects of cooling on contraction-induced peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) and vascular endothelial growth factor (VEGF) gene expression, phosphorylations of its related protein kinases, and metabolic responses. Male rats were separated into two groups; room temperature (RT) or ice-treated (COLD) on the right tibialis anterior (TA). The TA was contracted isometrically using nerve electrical stimulation (1-s stimulation × 30 contractions, with 1-s intervals, for 10 sets with 1-min intervals). The TA was treated before the contraction and during 1-min intervals with an ice pack for the COLD group and a water pack at RT for the RT group. The muscle temperature of the COLD group decreased to 19.42 ± 0.44°C (p < 0.0001, -36.4%) compared with the RT group after the experimental protocol. An increase in mRNA expression level of PGC-1α, not VEGF, after muscle contractions was significantly lower in the COLD group than in the RT group (p < 0.0001, -63.0%). An increase in phosphorylated AMP-activated kinase (AMPK) (p = 0.0037, -28.8%) and a decrease in glycogen concentration (p = 0.0231, +106.3%) after muscle contraction were also significantly inhibited by cooling. Collectively, muscle cooling attenuated the post-contraction increases in PGC-1α mRNA expression coinciding with decreases in AMPK phosphorylation and glycogen degradation.

Opto-thermal technologies for microscopic analysis of cellular temperature-sensing systems

Could enzymatic activities and their cooperative functions act as cellular temperature-sensing systems? This review introduces recent opto-thermal technologies for microscopic analyses of various types of cellular temperature-sensing system. Optical microheating technologies have been developed for local and rapid temperature manipulations at the cellular level. Advanced luminescent thermometers visualize the dynamics of cellular local temperature in space and time during microheating. An optical heater and thermometer can be combined into one smart nanomaterial that demonstrates hybrid function. These technologies have revealed a variety of cellular responses to spatial and temporal changes in temperature. Spatial temperature gradients cause asymmetric deformations during mitosis and neurite outgrowth. Rapid changes in temperature causes imbalance of intracellular Ca2+ homeostasis and membrane potential. Among those responses, heat-induced muscle contractions are highlighted. It is also demonstrated that the short-term heating hyperactivates molecular motors to exceed their maximal activities at optimal temperatures. We discuss future prospects for opto-thermal manipulation of cellular functions and contributions to obtain a deeper understanding of the mechanisms of cellular temperature-sensing systems.

In vivo cooling-induced intracellular Ca2+ elevation and tension in rat skeletal muscle

It is an open question as to whether cooling‐induced muscle contraction occurs in the in vivo environment. In this investigation, we tested the hypotheses that a rise in intracellular Ca²⁺ concentration ([Ca²⁺]i) and concomitant muscle contraction could be evoked in vivo by reducing muscle temperature and that this phenomenon would be facilitated or inhibited by specific pharmacological interventions designed to impact Ca²⁺‐induced Ca²⁺‐release (CICR). Progressive temperature reductions were imposed on the spinotrapezius muscle of Wistar rats under isoflurane anesthesia by means of cold fluid immersion. The magnitude, location, and temporal profile of [Ca²⁺]i were estimated using fura‐2 loading. Caffeine (1.25–5.0 mM) and procaine (1.6–25.6 mM) loading were applied in separatum to evaluate response plasticity by promoting or inhibiting CICR, respectively. Lowering the temperature of the muscle surface to ~5°C produced active tension and discrete sites with elevated [Ca²⁺]i. This [Ca²⁺]i elevation differed in magnitude from fiber to fiber and also from site to site within a fiber. Caffeine at 1.25 and 5.0 mM reduced the magnitude of cooling necessary to elevate [Ca²⁺]i (i.e., from ~5°C to ~8 and ~16°C, respectively, both p < 0.05) and tension. Conversely, 25.6 mM procaine lowered the temperature at which [Ca²⁺]i elevation and tension were detected to ~2°C (p < 0.05). Herein we demonstrate the spatial and temporal relationship between cooling‐induced [Ca²⁺]i elevation and muscle contractile force in vivo and the plasticity of these responses with CICR promotion and inhibition.

Mathematical Characterization of Protein Sequences Using Patterns as Chemical Group Combinations of Amino Acids

Comparison of amino acid sequence similarity is the fundamental concept behind the protein phylogenetic tree formation. By virtue of this method, we can explain the evolutionary relationships, but further explanations are not possible unless sequences are studied through the chemical nature of individual amino acids. Here we develop a new methodology to characterize the protein sequences on the basis of the chemical nature of the amino acids. We design various algorithms for studying the variation of chemical group transitions and various chemical group combinations as patterns in the protein sequences. The amino acid sequence of conventional myosin II head domain of 14 family members are taken to illustrate this new approach. We find two blocks of maximum length 6 aa as 'FPKATD' and 'Y/FTNEKL' without repeating the same chemical nature and one block of maximum length 20 aa with the repetition of chemical nature which are common among all 14 members. We also check commonality with another motor protein sub-family kinesin, KIF1A. Based on our analysis we find a common block of length 8 aa both in myosin II and KIF1A. This motif is located in the neck linker region which could be responsible for the generation of mechanical force, enabling us to find the unique blocks which remain chemically conserved across the family. We also validate our methodology with different protein families such as MYOI, Myosin light chain kinase (MLCK) and Rho-associated protein kinase (ROCK), Na+/K+-ATPase and Ca2+-ATPase. Altogether, our studies provide a new methodology for investigating the conserved amino acids' pattern in different proteins.

Multiscale Modeling Indicates That Temperature Dependent [Ca2+]i Spiking in Astrocytes Is Quantitatively Consistent with Modulated SERCA Activity

Changes in the cytosolic Ca(2+) concentration ([Ca(2+)]i) are the most predominant active signaling mechanism in astrocytes that can modulate neuronal activity and is assumed to influence neuronal plasticity. Although Ca(2+) signaling in astrocytes has been intensively studied in the past, our understanding of the signaling mechanism and its impact on tissue level is still incomplete. Here we revisit our previously published data on the strong temperature dependence of Ca(2+) signals in both cultured primary astrocytes and astrocytes in acute brain slices of mice. We apply multiscale modeling to test the hypothesis that the temperature dependent [Ca(2+)]i spiking is mainly caused by the increased activity of the sarcoendoplasmic reticulum ATPases (SERCAs) that remove Ca(2+) from the cytosol into the endoplasmic reticulum. Quantitative comparison of experimental data with multiscale simulations supports the SERCA activity hypothesis. Further analysis of multiscale modeling and traditional rate equations indicates that the experimental observations are a spatial phenomenon where increasing pump strength leads to a decoupling of Ca(2+) release sites and subsequently to vanishing [Ca(2+)]i spikes.

Piezoelectric Nanoparticle-Assisted Wireless Neuronal Stimulation

Tetragonal barium titanate nanoparticles (BTNPs) have been exploited as nanotransducers owing to their piezoelectric properties, in order to provide indirect electrical stimulation to SH-SY5Y neuron-like cells. Following application of ultrasounds to cells treated with BTNPs, fluorescence imaging of ion dynamics revealed that the synergic stimulation is able to elicit a significant cellular response in terms of calcium and sodium fluxes; moreover, tests with appropriate blockers demonstrated that voltage-gated membrane channels are activated. The hypothesis of piezoelectric stimulation of neuron-like cells was supported by lack of cellular response in the presence of cubic nonpiezoelectric BTNPs, and further corroborated by a simple electroelastic model of a BTNP subjected to ultrasounds, according to which the generated voltage is compatible with the values required for the activation of voltage-sensitive channels.

Microscopic heat pulse-induced calcium dynamics in single WI-38 fibroblasts

Temperature-sensitive Ca²⁺ dynamics occur primarily through transient receptor potential channels, but also by means of Ca²⁺ channels and pumps on the endoplasmic reticulum membrane. As such, cytoplasmic Ca²⁺ concentration ([Ca²⁺]_cyt) is re-equilibrated by changes in ambient temperature. The present study investigated the effects of heat pulses (heating duration: 2 s or 150 s) on [Ca²⁺]_cyt in single WI-38 fibroblasts, which are considered as normal cells. We found that Ca²⁺ burst occurred immediately after short (2 s) heat pulse, which is similar to our previous report on HeLa cells, but with less thermosensitivity. The heat pulses originated from a focused 1455-nm infrared laser light were applied in the vicinity of cells under the optical microscope. Ca²⁺ bursts induced by the heat pulse were suppressed by treating cells with inhibitors for sarco/endoplasmic reticulum Ca²⁺ ATPase (SERCA) or inositol trisphosphate receptor (IP₃R). Long (150 s) heat pulses also induced Ca²⁺ bursts after the onset of heating and immediately after re-cooling. Cells were more thermosensitive at physiological (37°C) than at room (25°C) temperature; however, at 37°C, cells were responsive at a higher temperature (ambient temperature+heat pulse). These results strongly suggest that the heat pulse-induced Ca²⁺ burst is caused by a transient imbalance in Ca²⁺ flow between SERCA and IP₃R, and offer a potential new method for thermally controlling Ca²⁺-regulated cellular functions.

Teleost fish models in membrane transport research: the PEPT1(SLC15A1) H+-oligopeptide transporter as a case study

Human genes for passive, ion-coupled transporters and exchangers are included in the so-called solute carrier (SLC) gene series, to date consisting of 52 families and 398 genes. Teleost fish genes for SLC proteins have also been described in the last two decades, and catalogued in preliminary SLC-like form in 50 families and at least 338 genes after systematic GenBank database mining (December 2010-March 2011). When the kinetic properties of the expressed proteins are studied in detail, teleost fish SLC transporters always reveal extraordinary 'molecular diversity' with respect to the mammalian counterparts, which reflects peculiar adaptation of the protein to the physiology of the species and/or to the environment where the species lives. In the case of the H+ -oligopeptide transporter PEPT1(SLC15A1), comparative analysis of diverse teleost fish orthologs has shown that the protein may exhibit very eccentric properties in terms of pH dependence (e.g., the adaptation of zebrafish PEPT1 to alkaline pH), temperature dependence (e.g., the adaptation of icefish PEPT1 to sub-zero temperatures) and/or substrate specificity (e.g., the species-specificity of PEPT1 for the uptake of l-lysine-containing peptides). The revelation of such peculiarities is providing new contributions to the discussion on PEPT1 in both basic (e.g., molecular structure-function analyses) and applied research (e.g., optimizing diets to enhance growth of commercially valuable fish).

Protein cold adaptation strategy via a unique seven-amino acid domain in the icefish (Chionodraco hamatus) PEPT1 transporter

Adaptation of organisms to extreme environments requires proteins to work at thermodynamically unfavorable conditions. To adapt to subzero temperatures, proteins increase the flexibility of parts of, or even the whole, 3D structure to compensate for the lower thermal kinetic energy available at low temperatures. This may be achieved through single-site amino acid substitutions in regions of the protein that undergo large movements during the catalytic cycle, such as in enzymes or transporter proteins. Other strategies of cold adaptation involving changes in the primary amino acid sequence have not been documented yet. In Antarctic icefish (Chionodraco hamatus) peptide transporter 1 (PEPT1), the first transporter cloned from a vertebrate living at subzero temperatures, we came upon a unique principle of cold adaptation. A de novo domain composed of one to six repeats of seven amino acids (VDMSRKS), placed as an extra stretch in the cytosolic COOH-terminal region, contributed per se to cold adaptation. VDMSRKS was in a protein region uninvolved in transport activity and, notably, when transferred to the COOH terminus of a warm-adapted (rabbit) PEPT1, it conferred cold adaptation to the receiving protein. Overall, we provide a paradigm for protein cold adaptation that relies on insertion of a unique domain that confers greater affinity and maximal transport rates at low temperatures. Due to its ability to transfer a thermal trait, the VDMSRKS domain represents a useful tool for future cell biology or biotechnological applications.

Modeling the contributions of Ca2+ flows to spontaneous Ca2+ oscillations and cortical spreading depression-triggered Ca2+ waves in astrocyte networks

Astrocytes participate in brain functions through Ca(2+) signals, including Ca(2+) waves and Ca(2+) oscillations. Currently the mechanisms of Ca(2+) signals in astrocytes are not fully clear. Here, we present a computational model to specify the relative contributions of different Ca(2+) flows between the extracellular space, the cytoplasm and the endoplasmic reticulum of astrocytes to the generation of spontaneous Ca(2+) oscillations (CASs) and cortical spreading depression (CSD)-triggered Ca(2+) waves (CSDCWs) in a one-dimensional astrocyte network. This model shows that CASs depend primarily on Ca(2+) released from internal stores of astrocytes, and CSDCWs depend mainly on voltage-gated Ca(2+) influx. It predicts that voltage-gated Ca(2+) influx is able to generate Ca(2+) waves during the process of CSD even after depleting internal Ca(2+) stores. Furthermore, the model investigates the interactions between CASs and CSDCWs and shows that the pass of CSDCWs suppresses CASs, whereas CASs do not prevent the generation of CSDCWs. This work quantitatively analyzes the generation of astrocytic Ca(2+) signals and indicates different mechanisms underlying CSDCWs and non-CSDCWs. Research on the different types of Ca(2+) signals might help to understand the ways by which astrocytes participate in information processing in brain functions.

Temperature and nitric oxide control spontaneous calcium transients in astrocytes

Transient spontaneous increases in the intracellular Ca2+ concentration have been frequently observed in astrocytes in cell culture and in acutely isolated slices from several brain regions. Recent in vivo experiments, however, reported only a low frequency of spontaneous Ca2+ events in astrocytes. Since the ex vivo experiments were usually performed at temperatures lower than physiological body temperature, we addressed the question whether temperature could influence the spontaneous Ca2+ activity in astrocytes. Indeed, comparing the frequency and spike width of spontaneous Ca2+ transients in astrocytes at temperatures between 20 and 37 degrees C in culture as well as in acute cortical slices from mouse brain, revealed that spontaneous Ca2+ responses occurred frequently at low temperature and became less frequent at higher temperature. Moreover, the single Ca2+ events had a longer duration at low temperature. We found that nitric oxide (NO) mimicked the increase in spontaneous Ca2+ activity and that an NO-synthase inhibitor attenuated the effect of lowering the temperature. Thus, temperature and NO are major determinants of spontaneous astrocytic Ca2+ signalling.

Calcium regulation in individual peripheral sensory nerve terminals of the rat

Ca2+ is vital for release of neurotransmitters and trophic factors from peripheral sensory nerve terminals (PSNTs), yet Ca2+ regulation in PSNTs remains unexplored. To elucidate the Ca2+ regulatory mechanisms in PSNTs, we determined the effects of a panel of pharmacological agents on electrically evoked Ca2+ transients in rat corneal nerve terminals (CNTs) in vitro that had been loaded with the fluorescent Ca2+ indicator, Oregon Green 488 BAPTA-1 dextran or fura-2 dextran in vivo. Inhibition of the sarco(endo)plasmic reticulum Ca2+-ATPase, disruption of mitochondrial Ca2+ uptake, or inhibition of the Na+-Ca2+ exchanger did not measurably alter the amplitude or decay kinetics of the electrically evoked Ca2+ transients in CNTs. By contrast, inhibition of the plasma membrane Ca2+-ATPase (PMCA) by increasing the pH slowed the decay of the Ca2+ transient by 2-fold. Surprisingly, the energy for ion transport across the plasma membrane of CNTs is predominantly from glycolysis rather than mitochondrial respiration, as evidenced by the observation that Ca2+ transients were suppressed by iodoacetate but unaffected by mitochondrial inhibitors. These observations indicate that, following electrical activity, the PMCA is the predominant mechanism of Ca2+ clearance from the cytosol of CNTs and glycolysis is the predominant source of energy.

Molecular biology of ion motive proteins in comparative models

This article will review the utility of comparative animal models in understanding the molecular biology of ion transport. Due to the breadth of this field some 'disclaimers' need to be established up front. 'Comparative' will be defined as non-mammalian. 'Genetic species' will be defined as organisms that have been selected as models for genetic studies and for which the genome has been largely sequenced. 'Non-genetic species' will include other non-mammalian organisms. The review will be limited to ions that play a major role in extracellular (EC) ionoregulation (Na/K/Ca/Cl) and not to micronutrients (Fe) or heavy metals (Cd, Zn). The review will focus only on ion motive proteins that have been associated with vectorial transfer at epithelial tissues. The review is therefore intended as a guidepost to researchers new to the field as well as to inform biologists of the power of comparative genomics.

Effect of orthophosphate, nucleotide analogues, ADP, and phosphorylation on the cytoplasmic domains of Ca(2+)-ATPase from scallop sarcoplasmic reticulum

The effects of orthophosphate, nucleotide analogues, ADP, and covalent phosphorylation on the tryptic fragmentation patterns of the E1 and E2 forms of scallop Ca-ATPase were examined. Sites preferentially cleaved by trypsin in the E1 form of the Ca-ATPase were detected in the nucleotide (N) and phosphorylation (P) domains, as well as the actuator (A) domain. These sites were occluded in the E2 (Ca(2+)-free) form of the enzyme, consistent with mutual protection of the A, N, and P domains through their association into a clustered structure. Similar protection of cytoplasmic Ca(2+)-dependent tryptic cleavage sites was observed when the catalytic binding site for substrate on the E1 form of scallop Ca-ATPase was occupied by Pi, AMP-PNP, AMP-PCP, or ADP despite the presence of saturating levels of Ca2+. These results suggest that occupation of the catalytic site on E1 can induce condensation of the cytoplasmic domains to yield a unique structural intermediate that may be related to the form of the enzyme in which the active site is prepared for phosphoryl transfer. The effect of Pi on the E2 form of the scallop Ca-ATPase was also investigated, when it was found that formation of E2-P led to extreme resistance toward secondary cleavage by trypsin and stabilization of enzymatic activity for long periods of time.

Characterisation of intestinal peptide transporter of the Antarctic haemoglobinless teleost Chionodraco hamatus

H(+)/peptide cotransport was studied in brush-border membrane vesicles (BBMV) from the intestine of the haemoglobinless Antarctic teleost Chionodraco hamatus by monitoring peptide-dependent intravesicular acidification with the pH-sensitive dye Acridine Orange. Diethylpyrocarbonate-inhibited intravesicular acidification was specifically achieved in the presence of extravesicular glycyl-L-proline (Gly-L-Pro) as well as of glycyl-L-alanine (Gly-L-Ala) and D-phenylalanyl-L-alanine (D-Phe-L-Ala). H(+)/Gly-L-Pro cotransport displayed saturable kinetics, involving a single carrier system with an apparent substrate affinity (K(m,app)) of 0.806+/-0.161 mmol l(-1). Using degenerated primers from eel and human (PepT1) transporter sequence, a reverse transcription-polymerase chain reaction (RT-PCR) signal was detected in C. hamatus intestine. RT-PCR paralleled kinetic analysis, confirming the hypothesis of the existence of a PepT1-type transport system in the brush-border membranes of icefish intestine. Functional expression of H(+)/peptide cotransport was successfully performed in Xenopus laevis oocytes after injection of poly(A)(+) RNA (mRNA) isolated from icefish intestinal mucosa. Injection of mRNA stimulated D-Phe-L-Ala uptake in a dose-dependent manner and an excess of glycyl-L-glutamine inhibited this transport. H(+)/peptide cotransport in the Antarctic teleost BBMV exhibited a marked difference in temperature optimum with respect to the temperate teleost Anguilla anguilla, the maximal activity rate occurring at approximately 0 degrees C for the former and 25 degrees C for the latter. Temperature dependence of icefish and eel intestinal mRNA-stimulated uptake in the heterologous system (oocytes) was comparable.

Molecular physiology of the SERCA and SPCA pumps

Intracellular Ca(2+)-transport ATPases exert a pivotal role in the endoplasmic reticulum and in the compartments of the cellular secretory pathway by maintaining a sufficiently high lumenal Ca(2+) (and Mn(2+)) concentration in these compartments required for an impressive number of vastly different cell functions. At the same time this lumenal Ca(2+) represents a store of releasable activator Ca(2+) controlling an equally impressive number of cytosolic functions. This review mainly focuses on the different Ca(2+)-transport ATPases found in the intracellular compartments of mainly animal non-muscle cells: the sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) pumps. Although it is not our intention to treat the ATPases of the specialized sarcoplasmic reticulum in depth, we can hardly ignore the SERCA1 pump of fast-twitch skeletal muscle since its structure and function is by far the best understood and it can serve as a guide to understand the other members of the family. In a second part of this review we describe the relatively novel family of secretory pathway Ca(2+)/Mn(2+) ATPases (SPCA), which in eukaryotic cells are primarily found in the Golgi compartment.