Neoteric Semiembedded ß-Tricalcium Phosphate Promotes Osteogenic Differentiation of Mesenchymal Stem Cells under Cyclic Stretch.

ß-Tricalcium phosphate (ß-TCP) is a bioactive material for bone regeneration, but its brittleness limits its use as a standalone scaffold. Therefore, continuous efforts are necessary to effectively integrate ß-TCP into polymers, facilitating a sturdy ion exchange for cell regulation. Herein, a novel semiembedded technique was utilized to anchor ß-TCP nanoparticles onto the surface of the elastic polymer, followed by hydrophilic modification with the polymerization of dopamine. Cell adhesion and osteogenic differentiation of mesenchymal stem cells (MSCs) under static and dynamic uniaxial cyclic stretching conditions were investigated. The results showed that the new strategy was effective in promoting cell adhesion, proliferation, and osteogenic induction by the sustained release of Ca2+ in the vicinity and creating a reasonable roughness. Specifically, released Ca2+ from ß-TCP could activate the calcium signaling pathway, which further upregulated calmodulin and calcium/calmodulin-dependent protein kinase II genes in MSCs. Meanwhile, the roughness of the membrane and the uniaxial cyclic stretching activated the PIEZO1 signaling pathway. Chemical and mechanical stimulation promotes osteogenic differentiation and increases the expression of related genes 2-8-fold. These findings demonstrated that the neoteric semiembedded structure was a promising strategy in controlling both chemical and mechanical factors of biomaterials for cell regulation.

Salt-Induced Early Changes in Photosynthesis Activity Caused by Root-to-Shoot Signaling in Potato.

Salinity is one of the most dangerous types of stress in agriculture. Acting on the root, salinity causes changes in physiological processes in the shoot, especially photosynthesis, which is crucial for plant productivity. In our study, we used potato plants, the most important crop, to investigate the role of salt-induced signals in changes in photosynthesis activity. We found a salt-induced polyphasic decrease in photosynthesis activity, and the earliest phase started several minutes after salt addition. We found that salt addition triggered rapid hydraulic and calcium waves from root to shoot, which occurred earlier than the first phase of the photosynthesis response. The inhibition of calcium signals by lanthanum decreased with the formation of rapid changes in photosynthesis. In addition to this, a comparison of the characteristic times of signal propagation and the formation of a response revealed the role of calcium waves in the modulation of rapid changes in photosynthesis. Calcium waves are activated by the ionic component of salinity. The salt-induced decrease in transpiration corresponds in time to the second phase of the photosynthetic response, and it can be the cause of this change. The accumulation of sodium in the leaves occurs a few hours after salt addition, and it can be the cause of the long-term suppression of photosynthesis. Thus, salinity modulates photosynthetic activity in plants in different ways: both through the activation of rapid distant signals and by reducing the water input and sodium accumulation.

RyR-mediated calcium release in hippocampal health and disease.

Hippocampal synaptic plasticity is widely considered the cellular basis of learning and spatial memory processes. This article highlights the central role of Ca2+ release from the endoplasmic reticulum (ER) in hippocampal synaptic plasticity and hippocampus-dependent memory in health and disease. The key participation of ryanodine receptor (RyR) channels, which are the principal Ca2+ release channels expressed in the hippocampus, in these processes is emphasized. It is proposed that the increased neuronal oxidative tone displayed by hippocampal neurons during aging or Alzheimer's disease (AD) leads to excessive activation of RyR-mediated Ca2+ release, a process that is highly redox-sensitive, and that this abnormal response contributes to and aggravates these deleterious conditions.

[Neuronal Calcium Sensor-1: A Zinc/Redox-Dependent Protein of Nervous System Signaling Pathways].

Intracellular calcium signaling is involved in regulating the key functional mechanisms of the nervous system. The control of neuronal excitability and plasticity by calcium ions underlies the mechanisms of higher nervous activity, and the mechanisms of this control are of particular interest to researchers. A family of highly specialized neuronal proteins described in recent decades can translate the information contained in calcium signals into the regulation of channels, enzymes, receptors, and transcription factors. Neuronal calcium sensor-1 (NCS-1) is the most common member of the family, which is intensely expressed in central nervous system (CNS) cells; and controls several vital processes, such as neuronal growth and survival, reception, neurotransmission, and synaptic plasticity. In addition to calcium ions, NCS-1 can bind the so-called mobile, or signaling intracellular zinc, an increased concentration of which is a characteristic feature of cells in oxidative stress. Zinc coordination under these conditions stimulates NCS-1 oxidation to form a disulfide dimer (dNCS-1) with altered functional properties. A combined effect of mobile zinc and an increased redox potential of the medium can thus induce aberrant NCS-1 activity, including signals that promote survival of neuronal cells or induce their apoptosis and, consequently, the development of neurodegenerative processes. The review details the localization, expression regulation, structure, and molecular properties of NCS-1 and considers the current data on its signaling activity in health and disease, including zinc-dependent redox regulation cascades.

Astrocytes and Alpha-Synuclein: Friend or Foe?

Despite its devastating disease burden and alarming prevalence, the etiology of Parkinson's disease (PD) remains to be completely elucidated. PD is characterized by the degeneration of dopaminergic neurons in the substantia nigra pars compacta and this correlates with the accumulation of misfolded α-synuclein. While the aggregation of α-synuclein in the form of Lewy bodies or Lewy neurites is a well-established intraneuronal hallmark of the disease process, our understanding of the glial contribution to aberrant α-synuclein proteostasis is lacking. In this regard, restoring astrocyte function during early PD could offer a promising therapeutic avenue and understanding the involvement of astrocytes in handling/mishandling of α-synuclein is of particular interest. Here, we explore the growing body of scientific literature implicating aberrant astrocytic α-synuclein proteostasis with the seemingly inexorable pathological sequelae typifying PD. We also provide a perspective on how heterogeneity in the morphological relationship between astrocytes and neurons will need to be considered in the context of PD pathogenesis.

Novel algorithms for improved detection and analysis of fluorescent signal fluctuations.

Fluorescent dyes and genetically encoded fluorescence indicators (GEFI) are common tools for visualizing concentration changes of specific ions and messenger molecules during intra- as well as intercellular communication. Using advanced imaging technologies, fluorescence indicators are a prerequisite for the analysis of physiological molecular signaling. Automated detection and analysis of fluorescence signals require to overcome several challenges, including correct estimation of fluorescence fluctuations at basal concentrations of messenger molecules, detection, and extraction of events themselves as well as proper segmentation of neighboring events. Moreover, event detection algorithms need to be sensitive enough to accurately capture localized and low amplitude events exhibiting a limited spatial extent. Here, we present two algorithms (PBasE and CoRoDe) for accurate baseline estimation and automated detection and segmentation of fluorescence fluctuations.

Human cancer cells generate spontaneous calcium transients and intercellular waves that modulate tumor growth.

Electrically excitable cells such as neurons transmit long-distance calcium or electrical signals to regulate their physiological functions. While the molecular underpinnings and down-stream effects of these intercellular communications in excitable cells have been well appreciated, little is known about whether and how non-excitable cancer cells spontaneously initiate and transmit long-distance intercellular signals. Here we report that non-excitable human colon and prostate cancer cells spontaneously initiate and spread intercellular calcium waves, in vitro and ex vivo. Xenograft model studies suggest that these calcium signals promote the growth rate of tumors in mice. Pharmacological studies elucidated that the inositol-trisphosphate-receptor (IP3R)-regulated calcium release from endoplasmic reticulum (ER), which is activated by the Gq-PLC-IP3R pathway, is a major cause for the initiation of spontaneous calcium transients. Further, the spatial-temporal characteristics of calcium dynamics can be tuned by the culture substrates of different mechanical stiffnesses. Our results provide evidence that calcium dynamics enables long-distance functional communication in non-excitable cancer cells and offer the potential to modulate calcium signaling for new cancer therapies.

Activation and Migration of Human Skeletal Muscle Stem Cells In Vitro Differently Rely on Calcium Signals.

Muscle regeneration is essential for proper muscle homeostasis and relies primarily on muscle stem cells (MuSC). MuSC are maintained quiescent in their niche and can be activated following muscle injury. Using an in vitro model of primary human quiescent MuSC (called reserve cells, RC), we analyzed their Ca2+ response following their activation by fetal calf serum and assessed the role of Ca2+ in the processes of RC activation and migration. The results showed that RC displayed a high response heterogeneity in a cell-dependent manner following serum stimulation. Most of these responses relied on inositol 1,4,5-trisphosphate (IP3)-dependent Ca2+ release associated with Ca2+ influx, partly due to store-operated calcium entry. Our study further found that blocking the IP3 production, Ca2+ influx, or both did not prevent the activation of RC. Intra- or extracellular Ca2+ chelation did not impede RC activation. However, their migration potential depended on Ca2+ responses displayed upon stimulation, and Ca2+ blockers inhibited their movement. We conclude that the two major steps of muscle regeneration, namely the activation and migration of MuSC, differently rely on Ca2+ signals.

Calcium signaling in neuroglia.

Glial cells exploit calcium (Ca2+) signals to perceive the information about the activity of the nervous tissue and the tissue environment to translate this information into an array of homeostatic, signaling and defensive reactions. Astrocytes, the best studied glial cells, use several Ca2+ signaling generation pathways that include Ca2+ entry through plasma membrane, release from endoplasmic reticulum (ER) and from mitochondria. Activation of metabotropic receptors on the plasma membrane of glial cells is coupled to an enzymatic cascade in which a second messenger, InsP3 is generated thus activating intracellular Ca2+ release channels in the ER endomembrane. Astrocytes also possess store-operated Ca2+ entry and express several ligand-gated Ca2+ channels. In vivo astrocytes generate heterogeneous Ca2+ signals, which are short and frequent in distal processes, but large and relatively rare in soma. In response to neuronal activity intracellular and inter-cellular astrocytic Ca2+ waves can be produced. Astrocytic Ca2+ signals are involved in secretion, they regulate ion transport across cell membranes, and are contributing to cell morphological plasticity. Therefore, astrocytic Ca2+ signals are linked to fundamental functions of the central nervous system ranging from synaptic transmission to behavior. In oligodendrocytes, Ca2+ signals are generated by plasmalemmal Ca2+ influx, or by release from intracellular stores, or by combination of both. Microglial cells exploit Ca2+ permeable ionotropic purinergic receptors and transient receptor potential channels as well as ER Ca2+ release. In this contribution, basic morphology of glial cells, glial Ca2+ signaling toolkit, intracellular Ca2+ signals and Ca2+-regulated functions are discussed with focus on astrocytes.

Survival upon Staphylococcus aureus mediated wound infection in Caenorhabditis elegans and the mechanism entailed.

Infection following injury is one of the major threats which causes huge economic burden in wound care management all over the world. Injury often results with poor healing when coupled by following infection. In contrast to this, we observed enhanced survival of wound infected worms compared to wounded worms in Caenorhabditis elegans wound model while infecting with Staphylococcus aureus. Hence, the study was intended to identify the mechanism for the enhanced survival of wound infected worms through LCMS/MS based high throughput proteomic analysis. Bioinformatics analyses of the identified protein players indicated differential enrichment of several pathways including MAPK signaling, oxidative phosphorylation and phosphatidylinositol signaling. Inhibition of oxidative phosphorylation and phosphatidylinositol signaling through chemical treatment showed complete reversal of the enhanced survival during wound infection nevertheless mutant of MAPK pathway did not reverse the same. Consequently, it was delineated that oxidative phosphorylation and phosphatidylinositol signaling are crucial for the survival. In this regard, elevated calcium signals and ROS including O- and H2O2 were observed in wounded and wound infected worms. Consequently, it was insinuated that presence of pathogen stress could have incited survival in wound infected worms with the aid of elevated ROS and calcium signals.

Calcium signals in astrocytes of the fly brain promote sleep.

Astrocytes are morphologically and functionally linked to neuronal synapses, and can regulate the activity of neural circuits, brain function, and behavior. However, the molecular mechanisms by which astrocytes regulate fundamental biological processes such as sleep are not completely understood. Wu and colleagues show that an increase in calcium signals within the processes of astrocytes of the fruit fly brain can promote sleep by upregulating the expression of a monoamine receptor, TyrRII, which in turn activates sleep promoting neurons via the astrocytic release of an interleukin-1 analog, spatzle. This study provides compelling evidence for a novel molecular mechanism by which increases in astrocytic calcium signals can induce sleep by activating sleep promoting neurons in the fly brain.

Age-Induced Differential Changes in the Central and Colonic Human Circadian Oscillators.

Aging modifies not only multiple cellular and homeostatic systems, but also biological rhythms. The circadian system is driven by a central hypothalamic oscillator which entrains peripheral oscillators, in both cases underlain by circadian genes. Our aim was to characterize the effect of aging in the circadian expression of clock genes in the human colon. Ambulatory recordings of the circadian rhythms of skin wrist temperature, motor activity and the integrated variable TAP (temperature, activity and position) were dampened by aging, especially beyond 74 years of age. On the contrary, quantitative analysis of genes expression in the muscle layer of colonic explants during 24 h revealed that the circadian expression of Bmal1, Per1 and Clock genes, was larger beyond that age. In vitro experiments showed that aging induced a parallel increase in the myogenic contractility of the circular colonic muscle. This effect was not accompanied by enhancement of Ca2+ signals. In conclusion, we describe here for the first time the presence of a molecular oscillator in the human colon. Aging has a differential effect on the systemic circadian rhythms, that are impaired by aging, and the colonic oscillator, that is strengthened in parallel with the myogenic contractility.

Aconitine induces cardiotoxicity through regulation of calcium signaling pathway in zebrafish embryos and in H9c2 cells.

Fuzi, the processed lateral roots of Aconitum carmichaelii Debx., is a traditional herbal medicine that is well known for its excellent pharmacological effects and acute toxicity. Aconitine is one of the diester-diterpene alkaloids and well-known for its arrhythmogenic effects. However, the effects of aconitine in zebrafish have rarely been studied. Therefore, we investigated the effects of aconitine on zebrafish embryos and H9c2 cells. Zebrafish embryos at 48 hours postfertilization were exposed to aconitine, and then, cardiac function and apoptosis were measured. Through transcriptomic analysis, the cardiotoxicity of aconitine in zebrafish embryos was involved in regulating Ca2+ signal pathways. A reverse transcription-polymerase chain reaction was performed to verify the expression of Ca2+ pathway-related genes after 12, 24, 36 and 48 hours of treatment. Meanwhile, intracellular Ca2+ concentrations and cell apoptosis were observed in H9c2 cells treated with half-maximal inhibitory concentration values of aconitine for 30 minutes. The protein levels of troponin T (TnT), caspase 3, Bcl-2 and Bax were detected by western blot analysis. In vivo, 2.0 and 8.0 µm aconitine decreased the heart rate and inhibited the contraction of ventricles and atria in a dose- and time-dependent manner. Furthermore, aconitine increased expression of cacna1c, RYR2, atp2a2b, Myh6, troponin C, p38, caspase 3, Bcl-2 and Bax for 12 hours. In vitro, 1.5 and 4.5 mm aconitine caused intracellular Ca2+ ion oscillation, increased rates of apoptosis, inhibited TnT and Bcl-2 protein expression, and promoted caspase 3 and Bax protein expression. These data confirmed that aconitine at various concentrations induced cardiac dysfunction and apoptosis were related to the Ca2+ signaling pathway.

Hair cell maturation is differentially regulated along the tonotopic axis of the mammalian cochlea.

KEY POINTS: Outer hair cells (OHCs) enhance the sensitivity and the frequency tuning of the mammalian cochlea. Similar to the primary sensory receptor, the inner hair cells (IHCs), the mature functional characteristics of OHCs are acquired before hearing onset. We found that OHCs, like IHCs, fire spontaneous Ca2+ -induced action potentials (APs) during immature stages of development, which are driven by CaV 1.3 Ca2+ channels. We also showed that the development of low- and high-frequency hair cells is differentially regulated during pre-hearing stages, with the former cells being more strongly dependent on experience-independent Ca2+ action potential activity. ABSTRACT: Sound amplification within the mammalian cochlea depends upon specialized hair cells, the outer hair cells (OHCs), which possess both sensory and motile capabilities. In various altricial rodents, OHCs become functionally competent from around postnatal day 7 (P7), before the primary sensory inner hair cells (IHCs), which become competent at about the onset of hearing (P12). The mechanisms responsible for the maturation of OHCs and their synaptic specialization remain poorly understood. We report that spontaneous Ca2+ activity in the immature cochlea, which is generated by CaV 1.3 Ca2+ channels, differentially regulates the maturation of hair cells along the cochlea. Under near-physiological recording conditions we found that, similar to IHCs, immature OHCs elicited spontaneous Ca2+ action potentials (APs), but only during the first few postnatal days. Genetic ablation of these APs in vivo, using CaV 1.3-/- mice, prevented the normal developmental acquisition of mature-like basolateral membrane currents in low-frequency (apical) hair cells, such as IK,n (carried by KCNQ4 channels), ISK2 and IACh (α9α10nAChRs) in OHCs and IK,n and IK,f (BK channels) in IHCs. Electromotility and prestin expression in OHCs were normal in CaV 1.3-/- mice. The maturation of high-frequency (basal) hair cells was also affected in CaV 1.3-/- mice, but to a much lesser extent than apical cells. However, a characteristic feature in CaV 1.3-/- mice was the reduced hair cell size irrespective of their cochlear location. We conclude that the development of low- and high-frequency hair cells is differentially regulated during development, with apical cells being more strongly dependent on experience-independent Ca2+ APs.

Measuring Sharp Waves and Oscillatory Population Activity With the Genetically Encoded Calcium Indicator GCaMP6f.

GCaMP6f is among the most widely used genetically encoded calcium indicators for monitoring neuronal activity. Applications are at both the cellular and population levels. Here, we explore two important and under-explored issues. First, we have tested if GCaMP6f is sensitive enough for the detection of population activity with sparse firing, similar to the sensitivity of the local field potential (LFP). Second, we have tested if GCaMP6f is fast enough for the detection of fast network oscillations critical for the encoding and consolidation of memory. We have focused this study on the activity of the hippocampal network including sharp waves (SWs), carbachol-induced theta oscillations, and interictal-like spikes. We compare simultaneous LFP and optical GCaMP6f fluorescent recordings in Thy1-GCaMP6f mouse hippocampal slices. We observe that SWs produce a clear population GCaMP6f signal above noise with an average magnitude of 0.3% ΔF/F. This population signal is highly correlated with the LFP, albeit with a delay of 40.3 ms (SD 10.8 ms). The population GCaMP6f signal follows the LFP evoked by 20 Hz stimulation with high fidelity, while electrically evoked oscillations up to 40 Hz were detectable with reduced amplitude. GCaMP6f and LFP signals showed a large amplitude discrepancy. The amplitude of GCaMP6f fluorescence increased by a factor of 28.9 (SD 13.5) between spontaneous SWs and carbachol-induced theta bursts, while the LFP amplitude increased by a factor of 2.4 (SD 1.0). Our results suggest that GCaMP6f is a useful tool for applications commonly considered beyond the scope of genetically encoded calcium indicators. In particular, population GCaMP6f signals are sensitive enough for detecting synchronous network events with sparse firing and sub-threshold activity, as well as asynchronous events with only a nominal LFP. In addition, population GCaMP6f signals are fast enough for monitoring theta and beta oscillations (<25 Hz). Faster calcium indicators (e.g., GCaMP7) will further improve the frequency response for the detection of gamma band oscillations. The advantage of population optical over LFP recordings are that they are non-contact and free from stimulation artifacts. These features may be particularly useful for high-throughput recordings and applications sensitive to stimulus artifact, such as monitoring responses during continuous stimulation.

Aberrant Calcium Signals in Reactive Astrocytes: A Key Process in Neurological Disorders.

Astrocytes are abundant cells in the brain that regulate multiple aspects of neural tissue homeostasis by providing structural and metabolic support to neurons, maintaining synaptic environments and regulating blood flow. Recent evidence indicates that astrocytes also actively participate in brain functions and play a key role in brain disease by responding to neuronal activities and brain insults. Astrocytes become reactive in response to injury and inflammation, which is typically described as hypertrophy with increased expression of glial fibrillary acidic protein (GFAP). Reactive astrocytes are frequently found in many neurological disorders and are a hallmark of brain disease. Furthermore, reactive astrocytes may drive the initiation and progression of disease processes. Recent improvements in the methods to visualize the activity of reactive astrocytes in situ and in vivo have helped elucidate their functions. Ca2+ signals in reactive astrocytes are closely related to multiple aspects of disease and can be a good indicator of disease severity/state. In this review, we summarize recent findings concerning reactive astrocyte Ca2+ signals. We discuss the molecular mechanisms underlying aberrant Ca2+ signals in reactive astrocytes and the functional significance of aberrant Ca2+ signals in neurological disorders.

Endothelin impacts on olfactory processing in rats.

In the olfactory epithelium, olfactory sensitive neurons and their axons are surrounded by glia-like cells called sustentacular cells, which maintain both the structural and ionic integrity of the olfactory mucosa. We have previously found that endothelin-1 (ET-1) can uncouple sustentacular cell gap junctions in vitro similarly as carbenoxolone, a known gap junction uncoupling agent. The role of gap junctions in odorant transduction remains controversial and we explored here if ET-1 naturally produced by the olfactory mucosa could impact odorant detection. Using calcium imaging on olfactory mucosa explant, we first confirmed that ET-1 uncouples gap junctions in an olfactory mucosa preparation preserving the tissue integrity. We next measured the olfactory epithelium responses to odorant stimulation using electro-olfactogram recordings. While the amplitude of the response was not modified by application of ET-1 and carbenoxolone, its repolarizing phase was slower after both treatments. We finally examined the behavioral performances of rat pups in an orientation test based on maternal odor recognition after intranasal instillations of ET-1 or carbenoxolone. While rat pups performances were decreased after ET-1 treatment, it was unchanged after carbenoxolone treatment. Overall, our results indicate that ET-1 modulates olfactory responses at least partly through gap junction uncoupling.

Developmental Increase of Neocortical Presynaptic Efficacy via Maturation of Vesicle Replenishment.

The efficacy of neocortical synapses to transmit during bursts of action potentials (APs) increases during development but the underlying mechanisms are largely unclear. We investigated synaptic efficacy at synapses between layer 5 pyramidal neurons (L5PNs) during development, using paired recordings, presynaptic two-photon Ca2+ imaging, and numerical simulations. Our data confirm a developmental increase in paired-pulse ratios (PPRs). Independent of age, Ca2+ imaging revealed no AP invasion failures and linear summation of presynaptic Ca2+ transients, making differences in Ca2+ signaling an unlikely reason for developmental changes in PPR. Cumulative excitatory postsynaptic current (EPSC) amplitudes indicate that neither the size of the readily-releasable pool (RRP) nor replenishment rates were different between age groups, while the time-courses of depression differed significantly. At young synapses, EPSCs depressed rapidly to near steady-state during the first four APs, and synaptic failures (Fsyn) increased from 0 to 30%. At mature synapses this drop was significantly slower and strongly biphasic, such that near steady-state depression was reached not before 18 APs with Fsyn remaining between 0 and 5%. While young synapses reliably transmitted during pairs of APs, albeit with strong depression, mature synapses maintained near 100% transfer efficacy with significantly less depression during high-frequency bursts of APs. Our analysis indicates that at mature synapses a replenishment pool (RepP) is responsible for their high efficacy during bursting activity, while this RepP is functionally immature at young synapses. Hence, our data provide evidence that the functional maturation of a RepP underlies increasing synaptic efficacy during the development of an excitatory cortical synapse.

Ryanodine Receptor-Mediated Calcium Release Has a Key Role in Hippocampal LTD Induction.

The induction of both long-term potentiation (LTP) and long-term depression (LTD) of synaptic transmission entails pre- and postsynaptic Ca2+ signals, which represent transient increments in cytoplasmic free Ca2+ concentration. In diverse synapse types, Ca2+ release from intracellular stores contributes to amplify the Ca2+ signals initially generated by activation of neuronal Ca2+ entry pathways. Here, we used hippocampal slices from young male rats to evaluate whether pharmacological activation or inhibition of Ca2+ release from the endoplasmic reticulum (ER) mediated by ryanodine receptor (RyR) channels modifies LTD induction at Schaffer collateral-CA1 synapses. Pre-incubation of slices with ryanodine (1 µM, 1 h) or caffeine (1 mM, 30 min) to promote RyR-mediated Ca2+ release facilitated LTD induction by low frequency stimulation (LFS), but did not affect the amplitude of synaptic transmission, the profiles of field excitatory postsynaptic potentials (fEPSP) or the paired-pulse (PP) responses. Conversely, treatment with inhibitory ryanodine (20 µM, 1 h) to suppress RyR-mediated Ca2+ release prevented LTD induction, but did not affect baseline synaptic transmission or PP responses. Previous literature reports indicate that LTD induction requires presynaptic CaMKII activity. We found that 1 h after applying the LTD induction protocol, slices displayed a significant increase in CaMKII phosphorylation relative to the levels exhibited by un-stimulated (naïve) slices. In addition, LTD induction (1 h) enhanced the phosphorylation of the presynaptic protein Synapsin I at a CaMKII-dependent phosphorylation site, indicating that LTD induction stimulates presynaptic CaMKII activity. Pre-incubation of slices with 20 µM ryanodine abolished the increased CaMKII and Synapsin I phosphorylation induced by LTD, whereas naïve slices pre-incubated with inhibitory ryanodine displayed similar CaMKII and Synapsin I phosphorylation levels as naïve control slices. We posit that inhibitory ryanodine suppressed LTD-induced presynaptic CaMKII activity, as evidenced by the suppression of Synapsin I phosphorylation induced by LTD. Accordingly, we propose that presynaptic RyR-mediated Ca2+ signals contribute to LTD induction at Schaffer collateral-CA1 synapses.

Guard cells in fern stomata are connected by plasmodesmata, but control cytosolic Ca2+ levels autonomously.

Recent studies have revealed that some responses of fern stomata to environmental signals differ from those of their relatives in seed plants. However, it is unknown whether the biophysical properties of guard cells differ fundamentally between species of both clades. Intracellular micro-electrodes and the fluorescent Ca2+ reporter FURA2 were used to study voltage-dependent cation channels and Ca2+ signals in guard cells of the ferns Polypodium vulgare and Asplenium scolopendrium. Voltage clamp experiments with fern guard cells revealed similar properties of voltage-dependent K+ channels as found in seed plants. However, fluorescent dyes moved within the fern stomata, from one guard cell to the other, which does not occur in most seed plants. Despite the presence of plasmodesmata, which interconnect fern guard cells, Ca2+ signals could be elicited in each of the cells individually. Based on the common properties of voltage-dependent channels in ferns and seed plants, it is likely that these key transport proteins are conserved in vascular plants. However, the symplastic connections between fern guard cells in mature stomata indicate that the biophysical mechanisms that control stomatal movements differ between ferns and seed plants.