Do we know the absolute values of intracellular free calcium concentration?

More than 20 years ago, it was shown that the addition of EGTA increases the affinity of the plasma membrane Ca2+ pump for Ca2+ by an order of magnitude. The left-hand shift of Ca2+-dependencies in the presence of EGTA has been also documented in studies of the sarcoplasmic reticulum Ca2+ pump, mitochondrial Ca2+-transporter as well as Ca2+-binding by calmodulin and troponin C. These data allow us to hypothesise that this effect is caused by an admixture of di- and trivalent cations possessing high affinity for EGTA and interacting with Ca2+-transporting and binding proteins. Here, we propose that polyvalent cations affect the estimation of absolute values of free intracellular Ca2+ concentration. Indeed, EGTA sharply increases the apparent affinity of the fluorescent Ca2+ indicators quin-2 and fluo-3 for Ca2+. The impact of polyvalent cations on Ca2+ measurement was further confirmed by the study showing the high sensitivity of Ca2+-induced fluo-3 fluorescence to Mn2+, Fe2+, Cu2+, and Co2+ seen in the absence of EGTA.     

Do stretch-induced changes in intracellular calcium modify the electrical activity of cardiac muscle?

Stretch of the myocardium influences the shape and amplitude of the intracellular Ca²⁺([Ca²⁺]_i) transient. Under isometric conditions stretch immediately increases myofilament Ca²⁺ sensitivity, increasing force production and abbreviating the time course of the [Ca²⁺]_i transient (the rapid response). Conversely, muscle shortening can prolong the Ca²⁺ transient by decreasing myofilament Ca²⁺ sensitivity. During the cardiac cycle, increased ventricular dilation may increase myofilament Ca²⁺ sensitivity during diastolic filling and the isovolumic phase of systole, but enhance the decrease in myofilament Ca²⁺ sensitivity during the systolic shortening of the ejection phase. If stretch is maintained there is a gradual increase in the amplitude of the Ca²⁺ transient and force production, which takes several minutes to develop fully (the slow response). The rapid and slow responses have been reported in whole hearts and single myocytes. Here we review stretch-induced changes in [Ca²⁺]_i and the underlying mechanisms.

Myocardial stretch also modifies electrical activity and the opening of stretch-activated channels (SACs) is often used to explain this effect. However, the myocardium has many ionic currents that are regulated by [Ca²⁺]_i and in this review we discuss how stretch-induced changes in [Ca²⁺]_i can influence electrical activity via the modulation of these Ca²⁺-dependent currents. Our recent work in single ventricular myocytes has shown that axial stretch prolongs the action potential. This effect is sensitive to either SAC blockade by streptomycin or the buffering of [Ca²⁺]_i with BAPTA, suggesting that both SACs and [Ca²⁺]_i are important for the full effects of axial stretch on electrical activity to develop.     

Subcellular propagation of calcium waves in Müller glia does not require autocrine/paracrine purinergic signaling

The polarized morphology of radial glia allows them to functionally interconnect different layers of CNS tissues including the retina, cerebellum, and cortex. A likely mechanism involves propagation of transcellular Ca²⁺ waves which were proposed to involve purinergic signaling. Because it is not known whether ATP release is required for astroglial Ca²⁺ wave propagation we investigated this in mouse Müller cells, radial astroglia-like retinal cells in which in which waves can be induced and supported by Orai/TRPC1 (transient receptor potential isoform 1) channels. We found that depletion of endoplasmic reticulum (ER) stores triggers regenerative propagation of transcellular Ca²⁺ waves that is independent of ATP release and activation of P₂X and P₂Y receptors. Both the amplitude and kinetics of transcellular, depletion-induced waves were resistant to non-selective purinergic P₂ antagonists such as pyridoxalphosphate-6-azophenyl-2′,4′-disulfonic acid (PPADS). Thus, store-operated calcium entry (SOCE) is itself sufficient for the initiation and subcellular propagation of calcium waves in radial glia.     

Can Lionel Messi’s brain slow down time passing?

It seems that seeing others in slow-motion by heroes does not belong only to movies. When Lionel Messi plays football, you can hardly see anything from him that other players cannot do. Then why he is not stoppable really? It seems the answer may be that opponents do not have enough time to do what they want; because in Messi’s neural system, time passes slower. In differential equations that model a single neuron, this speed can be generated by multiplying an equal term in all equations. Or maybe interactions between neurons and the structure of neural networks play this role.     

Do wild brown lemurs reconcile? Not always

Post-conflict behaviour has been widely investigated in anthropoid primates but not extensively in prosimians. Here, we report the reconciliation pattern of a 14-individual group of wild brown lemurs (Eulemur fulvus) in the Berenty gallery forest (South Madagascar). We found that reconciliation occurs only in the non-feeding context and that it works in reducing the risk of renewed aggression. Thus, reconciliation would provide an immediate positive feedback that is probably independent of the quality of the relationship between opponents. Reconciliation may also be a hic-et-nunc mechanism, needed to avoid conflict spreading across group members, possibly leading to social disruption.     

Do estrogens always increase breast cancer risk?

The etiology of breast cancer is closely linked to the female hormone estrogen, with high life-time exposure being suggested to increase breast cancer risk [Nature 303 (1983) 767]. However, there appears to be a disparity between studies attempting to establish an association between high estrogen levels and breast cancer risk. This disparity becomes smaller by taking into consideration a timing factor, and we propose that estrogens can increase, decrease, or have no effect on breast cancer risk, depending on the timing of estrogen exposure. We further propose that the timing of estrogenic exposures may play at least as important a role in affecting breast cancer risk as life-time exposure.     

Do temperature fluctuations during incubation always play an important role in shaping the phenotype of hatchling reptiles?

Fluctuating temperatures (FTs) influence hatchling phenotypes differently from constant temperatures (CTs) in some reptiles, but not in others. This inconsistency raises a question of whether thermal fluctuations during incubation always play an important role in shaping the phenotype of hatchlings. To answer this question, we incubated eggs of Naja atra under one CT (28 °C, CT), two temperature-shift [cold first (CF) and hot first (HF) in which eggs were first incubated at 24 or 32 °C and then at the other, each for 20 days, and finally at 28 °C until hatching], and one FT thermal regimes. Female hatchlings were larger in snout–vent length but smaller in tail length, head size than male hatchlings from the same-sized egg; female hatchlings had more ventral scales than did male hatchlings. The FT and HF treatments resulted in shorter incubation lengths. Tail length was greatest in the CT treatment and smallest in the FT treatment, with the CF and HF treatments in between; head width was greater in the CT treatment than in the other three treatments. Other examined hatchling traits did not differ among treatments. The observed morphological modifications cannot be attributed to the effect of thermal fluctuations but to the effect of temperatures close to the upper and lower viable limits for the species. Our results therefore support the hypothesis that hatchling phenotype is not altered by thermal fluctuation in species with no phenotypic response to incubation temperature within some thresholds.     

What is the role of astrocyte calcium in neurophysiology?

Astrocytes comprise approximately half of the volume of the adult mammalian brain and are the primary neuronal structural and trophic supportive elements. Astrocytes are organized into distinct nonoverlapping domains and extend elaborate and dense fine processes that interact intimately with synapses and cerebrovasculature. The recognition in the mid 1990s that astrocytes undergo elevations in intracellular calcium concentration following activation of G protein-coupled receptors by synaptically released neurotransmitters demonstrated not only that astrocytes display a form of excitability but also that astrocytes may be active participants in brain information processing. The roles that astrocytic calcium elevations play in neurophysiology and especially in modulation of neuronal activity have been intensely researched in recent years. This review will summarize the current understanding of the function of astrocytic calcium signaling in neurophysiological processes and discuss areas where the role of astrocytes remains controversial and will therefore benefit from further study.     

Is synaptotagmin the calcium sensor?

After much debate, recent progress indicates that the synaptic vesicle protein synaptotagmin I probably functions as the calcium sensor for synchronous neurotransmitter release. Following calcium influx into presynaptic terminals, synaptotagmin I rapidly triggers the fusion of synaptic vesicles with the plasma membrane and underlies the fourth-order calcium cooperativity of release. Biochemical and genetic studies suggest that lipid and SNARE interactions underlie synaptotagmin's ability to mediate the incredible speed of vesicle fusion that is the hallmark of fast synaptic transmission.     

Do predators influence the behaviour of bats?

Many aspects of animal behaviour are affected by real‐time changes in the risk of predation. This conclusion holds for virtually all taxa and ecological systems studied, but does it hold for bats? Bats are poorly represented in the literature on anti‐predator behaviour, which may reflect a lack of nocturnal predators specialized on bats. If bats actually experience a world with minimal anti‐predator concerns, then they will provide a unique contrast within the realm of vertebrate ecology. Alternatively, such predator‐driven behaviour in bats may not yet be fully understood, given the difficulties in working with these highly mobile and nocturnal animals. We provide a wide‐ranging exploration of these issues in bat behaviour. We first cover the basic predator‐prey information available on bats, both on potential predators and the ways in which bats might perceive predators and respond to attacks. We then cover work relevant to key aspects of bat behaviour, such as choice of daytime roosts, the nature of sleep and torpor, evening roost departures, moonlight avoidance, landscape‐related movement patterns, and habitat selection. Overall, the evidence in favour of a strong influence of predators on bat behaviour is equivocal, with the picture clouded by contradictory results and a lack of information on potential predators and the perception of risk by bats. It seems clear that day‐active bats run a considerable risk of being killed by diurnal raptors, which are able to capture bats with relative ease. Thus, bats taking advantage of a pulse of insects just prior to sunset are likely taking risks to gain much‐needed energy. Further, the choice of daytime roosts by bats is probably strongly influenced by roost safety. Few studies, however, have directly addressed either of these topics. As a group, insectivorous temperate‐zone bats show no clear tendency to avoid apparently risky situations, such as activity on moonlit nights. However, some observations are consistent with the idea that predation risk affects choice of movement paths and feeding areas by temperate‐zone bats, as well as the timing of roost departures. The behaviour of tropical bats, on the other hand, seems more generally influenced by predators; this is especially true for tropical nectarivores and frugivores, but also for insectivorous bats. Presumably there are more serious predators on bats in the tropics (e.g. specialized raptors or carnivorous bats), but the identity of these predators is unclear. More information is needed to assess fully the influence of predators on bat behaviour. There is much need for work on the ways in which bats perceive predators via auditory, visual, and olfactory cues, and whether bats have some knowledge of the risks posed by different predators. Also needed is information on how predators attack bats and how bats react to attacking predators. Difficult to obtain, but of critical value, will be information on the nature of the predation risk experienced by bats while away from roosts and during the full darkness of night.     

Bacterial flagella: Do they rotate or do they propagate waves of bending?

Conclusion Whether the flagellum is rigid or nearly so or whether there are moving helical lines of contraction (Astbury et al. 1955,Lowy andSpencer 1968), incompatible sets of bonds at different radii (Klug 1967), subunits which alter their configurational states (Asakura 1966, 1970) or slip between subunits carried by edge dislocations (Harris andScriven 1971, 1973), the prevention of apparent rotation of the flagellum will result in actual rotation of the body. The differences between the two classes of mechanisms have a scale beyond the power of resolution of the light microscope. Because of this it is most unlikely that direct observation of a moving bacterium will provide evidence favouring any one of the mechanisms. The mechanism of movement of bacterial flagella remains unknown.     

Do propagation methods affect the fine root architecture of African plum (Dacryodes edulis)?

Belowground tree growth attributes determine whether associations will be complementary or competitive in an agroforestry context. A study on fine root (d?≤?2?mm) distribution patterns of Dacryodes edulis based on root density (RD), root length density (RLD) and root weight density (RWD) was conducted to evaluate the effect of propagation methods on rooting distribution. Results showed that D. edulis trees of seed origin had greater RD (P?≤?0.001) than trees of vegetative origin (cuttings and marcots) in the upper soil stratum (0–30?cm). Similarly, in the uppermost soil stratum (0–10?cm), RLD and RWDs varied significantly (P?<?0.01). Trees of seed origin had an exponential distribution pattern for fine RD, RLD and RWD with depth to 80?cm. In contrast, the distribution pattern of fine roots of trees of vegetative origin (cuttings and marcots) were quadratic for the same variables which increased in the 20–30?cm soil depth stratum before declining steadily to a depth of 80?cm. The findings of this study suggest that D. edulis trees of vegetative origin (cuttings and marots) are likely to be less competitive than trees of seed origin when intercropped with shallow-rooted annual plants in an agroforestry system for belowground resources.     

Do bumblebees always forage as much as they could?

Summary Bumblebees must forage to provide food to the colony. However, foraging is costly as worker longevity is inversely related to foraging effort. Given this trade-off, workers from colonies with abundant food supplies could either maintain foraging to increase reserves for future use or forage less to avoid the associated costs. We tested these hypotheses over one summer, using 13 pairs of field colonies of Bombus impatiens. Half of the colonies were provided with a sucrose solution ad libitum and pollen at regular intervals throughout their entire development, while the other half served as controls. We measured the forager activity rates in colonies with infra-red motion detectors fit in nest box entrances. However, due to reasons beyond our control (loss of the queen, usurpation by Psithyrus, debris in the entrance tunnel, etc.), we could use data from only two pairs of colonies for the analysis. Food supplemented colonies had a forager activity rate per worker 25% lower than controls which supports the hypothesis that workers reduce risks when given the opportunity.Received 15 May 2003; revised 15 January 2004; accepted 19 February 2004.     

The regulation of autophagy by calcium signals: Do we have a consensus?

Macroautophagy (hereafter called ‘autophagy’) is a cellular process for degrading and recycling cellular constituents, and for maintenance of cell function. Autophagy initiates via vesicular engulfment of cellular materials and culminates in their degradation via lysosomal hydrolases, with the whole process often being termed ‘autophagic flux’. Autophagy is a multi-step pathway requiring the interplay of numerous scaffolding and signalling molecules. In particular, orthologs of the family of ∼30 autophagy-regulating (Atg) proteins that were first characterised in yeast play essential roles in the initiation and processing of autophagic vesicles in mammalian cells. The serine/threonine kinase mTOR (mechanistic target of rapamycin) is a master regulator of the canonical autophagic response of cells to nutrient starvation. In addition, AMP-activated protein kinase (AMPK), which is a key sensor of cellular energy status, can trigger autophagy by inhibiting mTOR, or by phosphorylating other downstream targets. Calcium (Ca²⁺) has been implicated in autophagic signalling pathways encompassing both mTOR and AMPK, as well as in autophagy seemingly not involving these kinases. Numerous studies have shown that cytosolic Ca²⁺ signals can trigger autophagy. Moreover, introduction of an exogenous chelator to prevent cytosolic Ca²⁺ signals inhibits autophagy in response to many different stimuli, with suggestions that buffering Ca²⁺ affects not only the triggering of autophagy, but also proximal and distal steps during autophagic flux. Observations such as these indicate that Ca²⁺ plays an essential role as a pro-autophagic signal. However, cellular Ca²⁺ signals can exert anti-autophagic actions too. For example, Ca²⁺ channel blockers induce autophagy due to the loss of autophagy-suppressing Ca²⁺ signals. In addition, the sequestration of Ca²⁺ by mitochondria during physiological signalling appears necessary to maintain cellular bio-energetics, thereby suppressing AMPK-dependent autophagy. This article attempts to provide an integrated overview of the evidence for the proposed roles of various Ca²⁺ signals, Ca²⁺ channels and Ca²⁺ sources in controlling autophagic flux.