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In the McMurdo Dry Valleys of Antarctica, stream biota is limited by the brief availability of liquid water. The benthic microbial mats harbor diatoms that have adapted to hydrologic stresses, including numerous endemic species. We found a strong relationship between diatom community composition and flow intermittency in a data set including seven streams that spanned a gradient in flow intermittency. In particular, two genera represented by numerous endemic species in Dry Valley habitats, Hantzschia and Luticola, had high abundances in moderately and highly intermittent streams, respectively. The Shannon Index of diversity was greatest in streams with intermediate flow intermittency, with lower diversity in more stable streams resulting from lower evenness, and lower diversity in highly intermittent streams resulting from lower richness. These results indicate that multiple metrics of biodiversity may be useful in assessing the response of diatom communities to changing hydrologic regime. We propose that flow intermittency acts as a species filter that increases habitat heterogeneity in Dry Valley streams and may allow endemic species to persist. Future Antarctic warming may alter diatom community composition and habitats that act as refugia for desiccation-tolerant taxa. Dans les vallees seches de McMurdo de l'Antarctique, les organismes des cours d'eau sont limites par la courte disponibilite d'eau liquide. Les tapis microbiens benthiques contiennent des diatomees, dont de nombreuses especes endemiques, qui se sont adaptees aux stress hydrologiques. Il existe une forte relation entre la composition de la communaute de diatomees et l' intermittence du debit dans un ensemble de donnees qui inclut sept cours d' eau qui couvrent un gradient de discontinuite du debit. En particulier, deux genres qui contiennent de nombreuses especes endemiques dans les habitats des vallees seches, Hantzschia et Luticola, atteignent de fortes abondances, respectivement dans les cours d'eau moyennement et fortement intermittents. L'indice de diversite de Shannon est maximal dans les cours d'eau qui ont un debit moderement discontinu; la diversite est plus basse dans les cours d'eau plus stables a cause d'une equitabilite plus faible et aussi plus basse dans les cours d'eau fortement intermittents a cause d'une richesse reduite. Ces resultats indiquent que l'utilisation de plusieurs metriques de la biodiversite peuvent etre utiles pour evaluer la reaction des communautes de diatomees aux changements de regime hydrologique. Nous croyons que la discontinuite du debit sert de filtre des especes, augmente l' heterogeneite des habitats dans les cours d' eau des vallees seches et peut permettre aux especes endemiques de survivre. Un rechauffement futur de l'Antarctique modifiera peut-etre les communautes de diatomees et les habitats qui servent de refuges pour les taxons tolerants a la dessiccation. [Traduit par la Redaction], Introduction Desert streams are characterized by intermittent flows, which influence the structure and function of stream communities (Robson et al. 2008; Larned et al. 2010; Roelke et al. 2012). In [...]

In superior cervical ganglion (SCG) neurons, stimulation of [M.sub.1] receptors ([M.sub.1]Rs) produces a distinct pattern of modulation of N-type calcium (N-) channel activity, enhancing currents elicited with negative test potentials and inhibiting currents elicited with positive test potentials. Exogenously applied arachidonic acid (AA) reproduces this profile of modulation, suggesting AA functions as a downstream messenger of [M.sub.1]Rs. In addition, techniques that diminish AA's concentration during [M.sub.1]R stimulation minimize N-current modulation. However, other studies suggest depletion of phosphatidylinositol-4,5-bisphosphate during [M.sub.1]R stimulation suffices to elicit modulation. In this study, we used an expression system to examine the physiological mechanisms regulating modulation. We found the [beta] subunit ([Ca.sub.V][beta]) acts as a molecular switch regulating whether modulation results in enhancement or inhibition. In human embryonic kidney 293 cells, stimulation of [M.sub.1]Rs or neurokinin-1 receptors (NK-1Rs) inhibited activity of N channels formed by [Ca.sub.V]2.2 and coexpressed with [Ca.sub.V][beta]1b, [Ca.sub.V][beta]3, or [Ca.sub.V][beta]4 but enhanced activity of N channels containing [Ca.sub.V][beta]2a. Exogenously applied AA produced the same pattern of modulation. Coexpression of [Ca.sub.V][beta]2a, [Ca.sub.V][beta]3, and [Ca.sub.V][beta]4 recapitulated the modulatory response previously seen in SCG neurons, implying heterogeneous association of [Ca.sub.V][beta] with [Ca.sub.V]2.2. Further experiments with mutated, chimeric [Ca.sub.V][beta] subunits and free palmitic acid revealed that palmitoylation of [Ca.sub.V][beta]2a is essential for loss of inhibition. The data presented here fit a model in which [Ca.sub.V][beta]2a blocks inhibition, thus unmasking enhancement. Our discovery that the presence or absence of palmitoylated [Ca.sub.V][beta]2a toggles [M.sub.1]R- or NK-1R-mediated modulation of N current between enhancement and inhibition identifies a novel role for palmitoylation. Moreover, these findings predict that at synapses, modulation of N-channel activity by [M.sub.1]Rs or NK-1Rs will fluctuate between enhancement and inhibition based on the presence of palmitoylated [Ca.sub.V][beta]2a. doi/10.1085/jgp.200910203

Global change drivers influence ecological processes at multiple scales and manifest across most of Earth as changes in biodiversity, biogeochemical cycles, infectious disease incidence, and ecohydrology. Small-scale investigations provide compelling evidence of specific effects of global change on local systems, but are of limited use in modeling complex ecological processes at continental-to-global scales. Long-term observations distributed across a diversity of habitat types are needed to improve the ability to forecast ecological change at large spatial and temporal scales. This special issue introduces the Terrestrial Observation System ( TOS) of the National Ecological Observatory Network ( NEON), a long-term, continental-scale ecological research platform designed to deliver these large-scale datasets. The TOS measures biodiversity of key biota (soil microbes, insects, plants, small mammals), ecosystem productivity and biogeochemistry, infectious disease dynamics, phenology, and population dynamics. The articles in this special issue describe the scientific rationale for the sampling designs of the TOS, including an overview of protocols, locations, and frequencies of measurements. The science designs are a culmination of design requirements scoped by NEON and the National Science Foundation, best available practices put forth by the scientific community, input from technical working groups, and consideration of logistical and financial constraints by NEON staff. Within each site, measurements have been collocated to the extent possible to optimize linkages among different sampling elements. Integrated analyses of terrestrial observations with sensor-based, imagery, and remote-sensing data collected by other NEON subsystems can facilitate scaling of measured parameters to larger spatial and temporal scales. NEON is designed to collect data for 30 years, and make these data freely available on a public data portal (). Samples and specimens will be archived and available to the scientific community upon request. The open access approach to the Observatory will provide users with the resources necessary to map, understand, and predict the effects of global change drivers on ecological processes at a continental scale. [ABSTRACT FROM AUTHOR]

Phorbol esters such as PMA activate protein kinase C (PKC), resulting in the block of N-type calcium (Ca) current inhibition via the membrane-delimited pathway. The site of convergence appears to occur at the I-II linker of the pore-forming subunit of the channel with phosphorylation antagonizing G-protein binding. The particular PKC isoform that modulates Ca current in superior cervical ganglion (SCG) neurons has not yet been identified. Maeno-Hikicki et al. (2003. Nature Neurosci. 6:468-475) demonstrated that the protein enigma homologue (enh) allows for specific anchoring of PKC[epsilon] to the carboxy-terminal tail of recombinant N-channels expressed in oocytes. The resulting channel complex augmented PKC modulation of Ca current, whereas inhibiting complex formation minimized modulation. Thus, PKC[epsilon] may be the primary PKC that mediates N-channel modulation. To determine whether this mechanism of N-channel modulation occurs in SCG neurons, we established which PKC isoforms are present in acutely dissociated neonatal SCG by Western blot analysis. At least 11 PKC isotorms are known and vary in their sensitivities to Ca and phorbol esters. The classical PKCs [alpha] [beta]I, [beta]II, and [gamma] are both Ca and phorbol ester sensitive, while the novel PKCs [delta], [epsilon], [theta], and [eta] are only phorbol ester sensitive and the atypical PKC's [zeta] and [iota]/[lambda] are insensitive to either Ca of phorbol esters. Our results are consistent with those found in cultured SCG neurons, confirming the presence of PKC [alpha], [beta]I, [beta]II, [delta], [epsilon], and [zeta] (Scholze et al. 2002. J. Neurosci. 22:5823-5832). We then established the presence of enh transcripts using RT-PCR. These preliminary findings indicate that both PKC[epsilon] and enh are present in the SCG. We are currently testing their role in PKC modulation of N-current in SCG neurons. (Supported by NIH grant RO1-NS34195.)

Calcium (Ca) currents and the M-type potassium current are modulated by an incompletely characterized diffusible second messenger pathway called the slow pathway. Great enthusiasm has greeted a recent hypothesis that PLC metabolism of phosphatidylinositol 4,5 bis-phosphate ([PIP.sub.2]), constitutively bound to channels, dissociates causing current inhibition; no further downstream processing of [PIP.sub.2] is required (Suh and Hille. 2002. Neuron 35:507-520; Wu et al. 2002. Nature. 419:947-952). In contrast, our data indicate that additional processing of [PIP.sub.2], is required for Ca current modulation. In addition to [M.sub.1] muscarinic receptors ([M.sub.1]Rs), [G.sub.q] and phospholipase C (PLC), we found phospholipase [A.sub.2] ([PLA.sub.2]) and a free fatty acid, most likely arachidonic acid (AA), appear to participate in L- and N-type Ca current inhibition (SGP abstract Liu, Roberts, and Rittenhouse). Demonstrating that [PLA.sub.2] is required tot Ca current inhibition by the slow pathway is critical for resolving the differences, if any, between these two models. Here, we use patch-clamp and molecular methods to determine which [PLA.sub.2] participates in L-current inhibition by the slow pathway in neonatal rat SCG neurons. Antibodies (Abs) selective for different [PLA2]s were dialyzed into neurons treated with [omega]-conotoxin-GVIA to block N-current. Type IV (c[PLA.sub.2]) or type VI (I[PLA.sub.2]) Abs, but not nonimmunized IgG or type IIa [PLA.sub.2] (s[PLA.sub.2]) Abs, minimized current inhibition by the muscarinic agonist oxotremorine-M (Oxo-M). Inhibition of FPL-64176 induced long-lasting L-type tail currents, normally observed with Oxo-M, was also minimized when the c[PLA.sub.2] Ab was dialyzed into cells. Western blot analysis revealed that the c[PLA.sub.2] Ab recognized a single band at the approximate molecular weight of c[PLA.sub.2]. PCR confirmed c[PLA.sub.2]'s presence in SCG consistent with Western blot analysis. These data identify, c[PLA.sub.2] as a necessary participant in [M.sub.1]R inhibition of L-current. We are currently probing the role of c[PLA.sub.2] further using gene knockout technology. (Supported by NIH RO1-NS 34195.)

Stimulation of postsynaptic M1 muscarinic receptors (M1Rs) increases firing rates of both sympathetic and central neurons that underlie increases in vasomotor tone, heart rate, and cognitive memory functioning. At the cellular level, M1R stimulation modulates currents through various voltage-gated ion channels, including KCNQ K+ channels (M-current) and both L- and N-type Ca2+ channels (L- and N-current) by a pertussis toxin-insensitive, slow signaling pathway. Depletion of phosphatidylinositol-4,5-bisphosphate (PIP2) during M1R stimulation suffices to inhibit M-current. We found previously that following PIP2 hydrolysis by phospholipase C, activation of phospholipase A2 and liberation of a lipid metabolite, most likely arachidonic acid (AA) are necessary for L- and N-current modulation. Here we examined the involvement of a third lipase, diacylglycerol lipase (DAGL), in the slow pathway. We documented the presence of DAGL in superior cervical ganglion neurons, and then tested the highly selective DAGL inhibitor, RHC-80267, for its capacity to antagonize M1R-mediated modulation of whole-cell Ca2+ currents. RHC-80267 significantly reduced L- and N-current inhibition by the muscarinic agonist oxotremorine-M (Oxo-M) but did not affect their inhibition by exogenous AA. Moreover, voltage-dependent inhibition of N-current by Oxo-M remained in the presence of RHC-80267, indicating selective action on the slow pathway. RHC also blocked inhibition of recombinant N-current. In contrast, RHC-80267 had no effect on native M-current inhibition. These data are consistent with a role for DAGL in mediating L- and N-current inhibition. These results extend our previous findings that the signaling pathway mediating L- and N-current inhibition diverges from the pathway initiating M-current inhibition. J. Cell. Physiol. 216: 91–100, 2008. © 2008 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Ion channels reside in a sea of phospholipids. During normal fluctuations in membrane potential and periods of modulation, lipids that directly associate with channel proteins influence gating by incompletely understood mechanisms. In one model, M1-muscarinic receptors (M1Rs) may inhibit both Ca2+ (L- and N-) and K+ (M-) currents by losing a putative interaction between channels and phosphatidylinositol-4,5-bisphosphate (PIP2). However, we found previously that M1R inhibition of N-current in superior cervical ganglion (SCG) neurons requires loss of PIP2 and generation of a free fatty acid, probably arachidonic acid (AA) by phospholipase A2 (PLA2). It is not known whether PLA2 activity and AA also participate in L- and M-current modulation in SCG neurons. To test whether PLA2 plays a similar role in M1R inhibition of L- and M-currents, we used several experimental approaches and found unanticipated divergent signaling. First, blocking resynthesis of PIP2 minimized M-current recovery from inhibition, whereas L-current recovered normally. Second, L-current inhibition required group IVa PLA2 [cytoplasmic PLA2 (cPLA2)], whereas M-current did not. Western blot and imaging studies confirmed acute activation of cPLA2 by muscarinic stimulation. Third, in type IIa PLA2 [secreted (sPLA2)]-/-/cPLA2-/- double-knock-out SCG neurons, muscarinic inhibition of L-current decreased. In contrast, M-current inhibition remained unaffected but recovery was impaired. Our results indicate that L-current is inhibited by a pathway previously shown to control M-current over-recovery after washout of muscarinic agonist. Our findings support a model of M1R-meditated channel modulation that broadens rather than restricts the roles of phospholipids and fatty acids in regulating ion channel activity. [ABSTRACT FROM AUTHOR]

In superior cervical ganglion (SCG) neurons, stimulation of M1 receptors (M1Rs) produces a distinct pattern of modulation of N-type calcium (N-) channel activity, enhancing currents elicited with negative test potentials and inhibiting currents elicited with positive test potentials. Exogenously applied arachidonic acid (AA) reproduces this profile of modulation, suggesting AA functions as a downstream messenger of M1Rs. In addition, techniques that diminish AA's concentration during M1R stimulation minimize N-current modulation. However, other studies suggest depletion of phosphatidylinositol-4,5-bisphosphate during M1R stimulation suffices to elicit modulation. In this study, we used an expression system to examine the physiological mechanisms regulating modulation. We found the β subunit (Cavβ) acts as a molecular switch regulating whether modulation results in enhancement or inhibition. In human embryonic kidney 293 cells, stimulation of M1Rs or neurokinin-1 receptors (NK-1Rs) inhibited activity of N channels formed by Cav2.2 and coexpressed with Cavβ1b, Cavβ3, or Cavβ4 but enhanced activity of N channels containing Cavβ2a. Exogenously applied AA produced the same pattern of modulation. Coexpression of Cavβ2a, Cavβ3, and Cavβ4 recapitulated the modulatory response previously seen in SCG neurons, implying heterogeneous association of Cavβ with Cav2.2. Further experiments with mutated, chimeric Caββ subunits and free palmitic acid revealed that palmitoylation of Cavβ2a is essential for loss of inhibition. The data presented here fit a model in which Cavβ2a blocks inhibition, thus unmasking enhancement. Our discovery that the presence or absence of palmitoylated Cavβ2a toggles M1R- or NK-1R-mediated modulation of N current between enhancement and inhibition identifies a novel role for palmitoylation. Moreover, these findings predict that at synapses, modulation of N-channel activity by M1Rs or NK-1Rs will fluctuate between enhancement and inhibition based on the presence of palmitoylated Cavβ2a. [ABSTRACT FROM AUTHOR]

Ion channels reside in a sea of phospholipids. During normal fluctuations in membrane potential and periods of modulation, lipids that directly associate with channel proteins influence gating by incompletely understood mechanisms. In one model, M(1)-muscarinic receptors (M(1)Rs) may inhibit both Ca(2+) (L- and N-) and K(+) (M-) currents by losing a putative interaction between channels and phosphatidylinositol-4,5-bisphosphate (PIP(2)). However, we found previously that M(1)R inhibition of N-current in superior cervical ganglion (SCG) neurons requires loss of PIP(2) and generation of a free fatty acid, probably arachidonic acid (AA) by phospholipase A(2) (PLA(2)). It is not known whether PLA(2) activity and AA also participate in L- and M-current modulation in SCG neurons. To test whether PLA(2) plays a similar role in M(1)R inhibition of L- and M-currents, we used several experimental approaches and found unanticipated divergent signaling. First, blocking resynthesis of PIP(2) minimized M-current recovery from inhibition, whereas L-current recovered normally. Second, L-current inhibition required group IVa PLA(2) [cytoplasmic PLA(2) (cPLA(2))], whereas M-current did not. Western blot and imaging studies confirmed acute activation of cPLA(2) by muscarinic stimulation. Third, in type IIa PLA(2) [secreted (sPLA(2))](-/-)/cPLA(2)(-/-) double-knock-out SCG neurons, muscarinic inhibition of L-current decreased. In contrast, M-current inhibition remained unaffected but recovery was impaired. Our results indicate that L-current is inhibited by a pathway previously shown to control M-current over-recovery after washout of muscarinic agonist. Our findings support a model of M(1)R-meditated channel modulation that broadens rather than restricts the roles of phospholipids and fatty acids in regulating ion channel activity.