High Speed Two-Photon Imaging of Calcium Dynamics in Dendritic Spines: Consequences for Spine Calcium Kinetics and Buffer Capacity

Rapid calcium concentration changes in postsynaptic structures are crucial for synaptic plasticity. Thus far, the determinants of postsynaptic calcium dynamics have been studied predominantly based on the decay kinetics of calcium transients. Calcium rise times in spines in response to single action potentials (AP) are almost never measured due to technical limitations, but they could be crucial for synaptic plasticity. With high-speed, precisely-targeted, two-photon point imaging we measured both calcium rise and decay kinetics in spines and secondary dendrites in neocortical pyramidal neurons. We found that both rise and decay kinetics of changes in calcium-indicator fluorescence are about twice as fast in spines. During AP trains, spine calcium changes follow each AP, but not in dendrites. Apart from the higher surface-to-volume ratio (SVR), we observed that neocortical dendritic spines have a markedly smaller endogenous buffer capacity with respect to their parental dendrites. Calcium influx time course and calcium extrusion rate were both in the same range for spines and dendrites when fitted with a dynamic multi-compartment model that included calcium binding kinetics and diffusion. In a subsequent analysis we used this model to investigate which parameters are critical determinants in spine calcium dynamics. The model confirmed the experimental findings: a higher SVR is not sufficient by itself to explain the faster rise time kinetics in spines, but only when paired with a lower buffer capacity in spines. Simulations at zero calcium-dye conditions show that calmodulin is more efficiently activated in spines, which indicates that spine morphology and buffering conditions in neocortical spines favor synaptic plasticity

The consequences of niche and physiological differentiation of archaeal and bacterial ammonia oxidisers for nitrous oxide emissions

The authors are members of the Nitrous Oxide Research Alliance (NORA), a Marie Skłodowska-Curie ITN and research project under the EU's seventh framework program (FP7). GN is funded by the AXA Research Fund and CGR by a Royal Society University Research Fellowship (UF150571) and a Natural Environment Research Council (NERC) Standard Grant (NE/K016342/1). The authors would like to thank Dr Robin Walker and the SRUC Craibstone Estate (Aberdeen) for access to the agricultural plots, Dr Alex Douglas for statistical advice and Philipp Schleusner for assisting microcosm construction and sampling.Peer reviewedPublisher PD

Draft genomes of gammaproteobacterial methanotrophs isolated from terrestrial ecosystems

Genome sequences of Methylobacter luteus, Methylobacter whittenburyi, Methylosarcina fibrata, Methylomicrobium agile, and Methylovulum miyakonense were generated. The strains represent aerobic methanotrophs typically isolated from various terrestrial ecosystems

Ion-Selectivity of Single Glutamate-Gated Channels in Locust Skeletal Muscle

ABSTRACT The ion-selectivity of the extrajunctional glutamate-gated ion channel in locust extensor tibiae muscle was studied using the patch-clamp technique. The alkali metal ions Li+, Na+, K+, Rb+ and Cs+ were all highly permeant, with reversal potentials close to 0mV. Both complete and partial replacement of Na+ (180 mmol I−1 in standard saline) showed that conductance (γ) increased in the order Li+&amp;lt; Na+&amp;lt; Cs+&amp;lt; Rb+ (approx. 70–125 pS), γK being close to γCs. The channel was impermeable to the large organic monovalent ions tetramethyl ammonium, guanidinium and choline, and permeable to the smaller ammonium ion. Divalent cations (Ca2+ and Mg2+) did not contribute measurably to the ionic current. Indications were obtained that high concentrations of Mg2+ or Ca2+ block the channel. The results suggest that the glutamate-gated channel combines a high conductance with a restricted ion-selectivity, based on ion charge and size, the conductance being dependent on the dehydration energy of the ionic species.</jats:p

Vasopressin/Oxytocin-Related Conopressin Induces Two Separate Pacemaker Currents in an Identified Central Neuron of<i>Lymnaea stagnalis</i>

van Soest, Paul F. and Karel S. Kits. Vasopressin/oxytocin-related conopressin induces two separate pacemaker currents in an identified central neuron of Lymnaea stagnalis. J. Neurophysiol. 78: 1384–1393, 1997. The molluscan vasopressin/oxytocin analogue Lys-conopressin excites neurons in the anterior lobe of the right cerebral ganglion of the snail Lymnaea stagnalis. Persistent inward currents that underlie the excitatory response were studied with the use of voltage-ramp protocols in the identified neuron RCB1 and other anterior lobe neurons. Under whole cell voltage-clamp conditions, two types of conopressin-activated current could be distinguished on the basis of their voltage dependence: 1) a pacemaker-like current that was activated at potentials above –40 mV (high-voltage-activated current, IHVA) and 2) an inward current that was activated at all potentials between –90 and +10 mV (low-voltage-activated current, ILVA). Ion substitution experiments indicate that sodium is the main charge carrier for IHVAand ILVA. Both currents are differentially affected by cadmium. IHVAand ILVAdiffer in dose dependence, with median effective concentration values of 7.7 × 10−8M and 2.2 × 10−7M, respectively. Vasopressin and oxytocin act as weak agonists for the conopressin responses. The kinetics of desensitization and washout of IHVAand ILVAare different. The HVA response shows little desensitization, whereas the LVA response desensitizes within minutes (time constant80 ± 28 s, mean ± SD). The time constant of washout on removal of conopressin is 159 ± 63 s for IHVAand 36 ± 13 s for ILVA. These results suggest that two distinct conopressin receptors are involved in the activation of both currents. The conopressin-activated currents induce or enhance a region of negative slope resistance in the steady-state current-voltage relation. They differ from a third persistent inward current that is carried by calcium and completely blocked by cadmium. The presumed functional roles of these currents, possibly including autoregulation, are discussed.</jats:p