The cellular toxicity of carbon-based nanomaterials was studied as a function of their aspect ratio and surface chemistry. These structures were multiwalled carbon nanotubes, carbon nanofibers, and carbon nanoparticles. Their toxicity was tested in vitro on lung tumor cells. Our work clearly indicated that these materials are toxic while the hazardous effect is size-dependent. Moreover, cytotoxicity is enhanced when the surface of the particles is functionalized after an acid treatment.

Calretinin (CR), calbindin D-28k (CB) and parvalbumin (PV) belong to the large family of EF-hand calcium-binding proteins, which comprises more than 200 members in man. Structurally these proteins are characterized by the presence of a variable number of evolutionary well-conserved helix-loop-helix motives, which bind Ca2+ ions with high affinity. Functionally, they fall into two groups: by interaction with target proteins, calcium sensors translate calcium concentrations into signaling cascades, whereas calcium buffers are thought to modify the spatiotemporal aspects of calcium transients. Although CR, CB and PV are currently being considered calcium buffers, this may change as we learn more about their biology. Remarkable differences in their biophysical properties have led to the distinction of fast and slow buffers and suggested functional specificity of individual calcium buffers. Evaluation of the physiological roles of CR, CB and PV has been facilitated by the recent generation of mouse strains deficient in these proteins. Here, we review the biology of these calcium-binding proteins with distinct reference to the cerebellum, since they are particularly enriched in specific cerebellar neurons. CR is principally expressed in granule cells and their parallel fibres, while PV and CB are present throughout the axon, soma, dendrites and spines of Purkinje cells. PV is additionally found in a subpopulation of inhibitory interneurons, the stellate and basket cells. Studies on deficient mice together with in vitro work and their unique cell type-specific distribution in the cerebellum suggest that these calcium-binding proteins have evolved as functionally distinct, physiologically relevant modulators of intracellular calcium transients. Analysis of different brain regions suggests that these proteins are involved in regulating calcium pools critical for synaptic plasticity. Surprisingly, a major role of any of these three calcium-binding proteins as an endogenous neuroprotectant is not generally supported.

No abstract

GABAergic (GABA ‫؍‬ ␥-aminobutyric acid) neurons from different brain regions contain high levels of parvalbumin, both in their soma and in their neurites. Parvalbumin is a slow Ca 2؉ buffer that may affect the amplitude and time course of intracellular Ca 2؉ transients in terminals after an action potential, and hence may regulate short-term synaptic plasticity. To test this possibility, we have applied paired-pulse stimulations (with 30-to 300-ms intervals) at GABAergic synapses between interneurons and Purkinje cells, both in wild-type (PV؉͞؉) mice and in parvalbumin knockout (PV؊͞؊) mice. We observed pairedpulse depression in PV؉͞؉ mice, but paired-pulse facilitation in PV؊͞؊ mice. In paired recordings of connected interneuronPurkinje cells, dialysis of the presynaptic interneuron with the slow Ca 2؉ buffer EGTA (1 mM) rescues paired-pulse depression in PV؊͞؊ mice. These data show that parvalbumin potently modulates short-term synaptic plasticity.GABA ͉ cerebellum ͉ basket cells ͉ stellate cells ͉ Purkinje cells T he immediate consequences of past neuronal activity on synaptic strength are often examined by measuring the ratio (called paired-pulse ratio, or PPR) between the mean synaptic current in response to a test stimulation over that obtained with a conditioning stimulus. If the PPR is larger than 1, the synapse is considered as facilitating, whereas values smaller than 1 are characteristic of depressing synapses. However, facilitation and depression presumably coexist in all experimental conditions, and the PPR that is measured may be viewed as a balance between these two competing processes (1, 2).Current hypotheses link facilitation to the fact that some of the Ca 2ϩ ions entering the presynaptic terminal during the first stimulus are still present when the second stimulus is delivered (3, 4). Several modes of action have been envisaged for the residual calcium. It could act by binding to high affinity sites of the normal exocytosis machinery (5), by binding to special sites responsible for facilitation (2, 6), or by modulating the degree of saturation of high affinity Ca 2ϩ buffers (7, 8), but direct evidence in favor of any of these possibilities is still lacking.Depression is a complex phenomenon including both pre-and postsynaptic components. It may involve depletion of a readily releasable pool of vesicles, saturation or desensitization of postsynaptic receptors, or still other processes (7, 9).Calcium-binding proteins such as parvalbumin (PV), calretinin, and calbindin D 28k are important modulators of intracellular calcium dynamics in neurons (10) and could therefore influence both facilitation and depression. Effects of these calcium buffers are determined by their affinities for Ca 2ϩ ions and by the kinetics (on and off rates) of binding and releasing of Ca 2ϩ . PV is in this regard interesting because it has a slow dissociation rate (about 1 s Ϫ1 ) and a slow apparent association rate (about 10 7 M Ϫ1 ⅐s Ϫ1 ), due to the fact that Mg 2ϩ ions compete with Ca 2ϩ ions for binding. As a result...

It is generally thought that transmitter release at mammalian central synapses is triggered by Ca2+ microdomains, implying loose coupling between presynaptic Ca2+ channels and Ca2+ sensors of exocytosis. Here we show that Ca2+ channel subunit immunoreactivity is highly concentrated in the active zone of GABAergic presynaptic terminals of putative parvalbumin-containing basket cells in the hippocampus. Paired recording combined with presynaptic patch pipette perfusion revealed that GABA release at basket cell-granule cell synapses is sensitive to millimolar concentrations of the fast Ca2+ chelator BAPTA but insensitive to the slow Ca2+ chelator EGTA. These results show that Ca2+ source and Ca2+ sensor are tightly coupled at this synapse, with distances in the range of 10-20 nm. Models of Ca2+ inflow-exocytosis coupling further reveal that the tightness of coupling increases efficacy, speed, and temporal precision of transmitter release. Thus, tight coupling contributes to fast feedforward and feedback inhibition in the hippocampal network.

Gene mutations and gene copy number variants are associated with autism spectrum disorders (ASDs). Affected gene products are often part of signaling networks implicated in synapse formation and/or function leading to alterations in the excitation/inhibition (E/I) balance. Although the network of parvalbumin (PV)-expressing interneurons has gained particular attention in ASD, little is known on PV's putative role with respect to ASD. Genetic mouse models represent powerful translational tools for studying the role of genetic and neurobiological factors underlying ASD. Here, we report that PV knockout mice (PV−/−) display behavioral phenotypes with relevance to all three core symptoms present in human ASD patients: abnormal reciprocal social interactions, impairments in communication and repetitive and stereotyped patterns of behavior. PV-depleted mice also showed several signs of ASD-associated comorbidities, such as reduced pain sensitivity and startle responses yet increased seizure susceptibility, whereas no evidence for behavioral phenotypes with relevance to anxiety, depression and schizophrenia was obtained. Reduced social interactions and communication were also observed in heterozygous (PV+/−) mice characterized by lower PV expression levels, indicating that merely a decrease in PV levels might be sufficient to elicit core ASD-like deficits. Structural magnetic resonance imaging measurements in PV−/− and PV+/− mice further revealed ASD-associated developmental neuroanatomical changes, including transient cortical hypertrophy and cerebellar hypoplasia. Electrophysiological experiments finally demonstrated that the E/I balance in these mice is altered by modification of both inhibitory and excitatory synaptic transmission. On the basis of the reported changes in PV expression patterns in several, mostly genetic rodent models of ASD, we propose that in these models downregulation of PV might represent one of the points of convergence, thus providing a common link between apparently unrelated ASD-associated synapse structure/function phenotypes.

The calcium-binding protein parvalbumin (PV) occurs at high concentrations in fast-contracting vertebrate muscle fibers. Its putative role in facilitating the rapid relaxation of mammalian fast-twitch muscle fibers by acting as a temporary buffer for Ca2+ is still controversial. We generated knockout mice for PV (PV −/−) and compared the Ca2+ transients and the dynamics of contraction of their muscles with those from heterozygous (PV +/−) and wild-type (WT) mice. In the muscles of PV-deficient mice, the decay of intracellular Ca2+ concentration ([Ca2+]i) after 20-ms stimulation was slower compared with WT mice and led to a prolongation of the time required to attain peak twitch tension and to an extension of the half-relaxation time. The integral [Ca2+]iin muscle fibers of PV −/− mice was higher and consequently the force generated during a single twitch was ∼40% greater than in PV +/− and WT animals. Acceleration of the contraction-relaxation cycle of fast-twitch muscle fibers by PV may confer an advantage in the performance of rapid, phasic movements.

Advances in the understanding of a class of Ca(2+)-binding proteins usually referred to as "Ca(2+) buffers" are reported. Proteins historically embraced within this group include parvalbumins (alpha and beta), calbindin-D9k, calbindin-D28k and calretinin. Within the last few years a wealth of data has accumulated that allow a better understanding of the functions of particular family members of the >240 identified EF-hand Ca(2+)-binding proteins encoded by the human genome. Studies often involving transgenic animal models have revealed that they exert their specific functions within an intricate network consisting of many proteins and cellular mechanisms involved in Ca(2+) signaling and Ca(2+) homeostasis, and are thus an essential part of the Ca(2+) homeostasome. Recent results indicate that calbindin-D28k, possibly also calretinin and oncomodulin, the mammalian beta parvalbumin, might have additional Ca(2+) sensor functions, leaving parvalbumin and calbindin-D9k as the only "pure" Ca(2+) buffers.