Delta Sites Research Articles

The narrow shelf concept: couplings and fluxes

The continental shelf domain has the nearshore zone as land-ward boundary while the shelf slope plays the role of sea-ward boundary. Shelf dynamics are, therefore, influenced by terrestrial and marine processes and are an important component for any integrated assessment of the coastal zone. The quantitative influence of nearshore/slope processes is, however, seldom considered and many continental shelves are considered “wide” (e.g. parts of the North Sea coast) or “narrow” (e.g. parts of the Mediterranean coast) based on intuition and implicit knowledge. No objective and quantitative assessment of the relevance of such processes in controlling the resulting shelf dynamics has been presented so far. The main aim of this paper is to examine the mechanisms “isolating” and “linking” the shelf to its neighbouring domains (viz. nearshore and slope) and, from this, to obtain a “natural” definition of the shelf category. The resulting critical shelf width, dividing shelves controlled by “border” processes from those controlled by their internal dynamics, turns out to depend on the considered process and its associated time/space scales. The paper will, thus, start by presenting the main mechanisms isolating shelf and slope, viz. the geostrophic and potential vorticity “constraint”. This will be followed by a discussion of the main processes linking shelf and slope, viz. non-linearities, boundary layer and unsteadiness effects and stratification. The same approach will be applied to the analysis of shelf and nearshore links, highlighting the distinction between isolating and coupling mechanisms. From this a “natural” evaluation of the critical shelf width will emerge, allowing a hierarchical classification of the various shelf width assessments and illustrating the relative importance of the different processes involved for the Ebro delta coastal sea (Spanish Mediterranean coast). The performed theoretical analysis, although based on field observations from the Ebro delta site, is also expected to be of use for other shelf environments, where there is a need to distinguish between the competing influences of nearshore and slope “boundaries”.

Reexamination of the Lung Khê Citadel in the Red River Delta

The Lung Khê Citadel site is located on the natural levee of the old Dâu River at Lung Khê hamlet, Thành Khu'o'ng village, Thuân Thành district in Bac Ninh Province. The citadel includes a large rectangular walled fort (north wall: 680m, south wall: 520m, east wall: 320m, west wall: 328m).Previous studies have identified the Lung Khê Citadel as the central citadel of Luy Lâu district, which was established as the capital of Chiao Chih (Giao Chi) Prefecture in the Western Han period and was also a place where Si Nhiêp, the prefect of Chiao Chih, resided. Recent studies have reshuffled the previous understanding.Excavations and field research have revealed that the citadel was built in the 2nd century AD and continuous occupation can be confirmed to the end of the 5th or early 6th century AD. A large-scaled bronze workshop has been confirmed in the north central area inside the walls. A mold fragment of a bronze drum found in this area indicates a part of the workshop was used for casting late Heger I type drums. Although the majority of the artifacts are of Chinese-origin, several types, such as end roof tiles, a table-shaped stone mortar (pesani) and kendi, show cultural affinity with artifacts found in Trà Kiêu and Óc Eo, where the early Southeast Asian states were formed.Among the early citadels or fort sites in the Red River Delta, Lung Khe is the largest one next to Cô Loa. The construction of Cô Loa can be dated between the 1st century BC and 1st century AD, but it seems that after its construction Cô Loa was not used for a very long time. On the other hand, the scale, occupation period and material culture of Lung Khê are worthy of the central capital of the Red River Delta, which must have been Long Bien. While there are many historical or legendary relics of Si Nhiêp around Lung Khê, no early document mentions any relation between Si Nhiêp and Luy Lâu. The title Long Ben Hâu conferred to Si Nhiêp as the lord of the district recorded in the San kuo chih is supporting evidence for this hypothesis.The development of the Nan Hai trade from the end of the 1st millennium BC between China and Southeast Asia or further west stimulated the socio-economic development of the Red River Delta as an entrepôt, and the political power at Lung Khê should have been related to trade. However, from the late 3rd or 4th century a change in the trade route may have brought about a decline in the economic position of the Red River Delta. The later period of the Lung Khê Citadel were less connected with the south, so more domestic factors inside the Red River Delta need to be understood in a historical context.

Recent environmental change in North African wetland lakes: diatom and other stratigraphic evidence from nine sites in the CASSARINA Project

All nine wetland lakes in the CASSARINA North African suite of sample sites have been disturbed strongly by human activity during the 20th century. Dated lake sediment core were used to provide evidence of the extent of recent environmental change at each site. Sedimentary diatoms at seven sites were useful for inferring salinity change trends during the last century. At two sites preservation problems severely degraded the sedimentary diatom record. Sediment core integrity was otherwise established. Lithostratigraphic measurements indicated some site specific changes in soil erosion and sediment composition but, for the Egyptian Delta lakes, no physical signal synchronous with Aswan High Dam construction was found. Sedimentary diatom assemblages were generally site characteristic and halophilous taxa were common. At two sites planktonic diatoms indicated some recent eutrophication but generally the assemblages were more indicative of salinity changes. Diatom-inferred salinity trends for the seven sites typically indicated that reductions in water salinity occurred sometime during the early or mid 20th century. Rather than climate, hydrological modification of water resources is implicated as the primary driver of salinity changes during most of the 20th century. In the western North African region these modifications were mainly local land drainage and water diversion programmes to alleviate winter flooding and/or promote summer water availability. In the Delta region, the Nile has been intensively exploited since antiquity and intensively so from the late 19th century to release more fresh water for agriculture. Here, diatom records indicate that freshening began well before the Aswan High Dam but salinity fluctuations have tended to diminish during the latter part of the 20th century. A small reversal in the water freshening trend in the 1980/90s was possibly a response to land subsidence/sea-level change or to reduced freshwater supply. Freshwater supply to the sites is generally diminishing as former freshwater surpluses switch to deficit. One site (Merja Bokka, Morocco) became completely dry in 1998 as agriculture encroached and Megene Chitane, the only acid lake in Tunisia, is currently affected by excessive inflow abstraction. At the beginning of the 21st century, eight of the nine CASSARINA sites persist as viable but modified aquatic ecosystems. They nevertheless continue to support valuable aquatic biodiversity, especially in the Delta sites and in Chitane. The modern diatom communities are clearly tolerant of considerable environmental change but the remaining sites are increasingly threatened by major hydrological disturbance. Base-line floristic data for the late 20th century are given but continuous biomonitoring combined with effective management is needed urgently to help conserve North Africa's diminishing natural wetland lake resources.

Novel Protein Kinase C .DELTA. Isoform Insensitive to Caspase-3.

Protein kinase C delta (PKC delta) plays a key regulatory role in a variety of cellular functions, including apoptosis, as well as cell growth and differentiation. We previously reported that apoptosis was induced by pretreatment with 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7), an inhibitor of PKC, in mouse thymocytes. In the present study, we showed that a novel PKC delta isoform (PKC deltaII) was transiently expressed when thymocytes were pretreated with H-7. The analysis of the cDNA encoding PKC deltaII indicated that a 78 bp fragment was inserted into the caspase-3 sensitive site of the original PKC delta (PKC deltaI), presumably by alternative splicing. The PKC deltaII expressed in COS-1 cells was one product with a molecular mass of 81 kDa and with kinase activity similar to that of PKC deltaI. The expressed PKC deltaI protein (78 kDa) was in part cleaved into a 38 kDa fragment in vivo and in vitro, but the PKC deltaII protein was not. Cleavage of the PKC deltaI protein was inhibited by a specific inhibitor of caspase-3, indicating that PKC deltaII is insensitive to caspase-3. The PKC deltaII was highly expressed in the testis and ovary, and at a lower level in the thymocytes, brain and kidney, whereas PKC deltaI was detected in most tissues, suggesting that the function of PKC deltaII is different from that of PKC deltaI.

Radiometrically determined dates and sedimentation rates for recent sediments in nine North African wetland lakes (the CASSARINA Project)

Sediment cores were collected from nine wetland lakes in Morocco, Tunisia and Egypt for the CASSARINA project investigating environmental change in Northern African wetlands. The cores were dated radiometrically by using natural (210Pb) and artificial (137Cs and 241Am) radionuclides. At sites in Morocco and Tunisia with mean annual rainfall totals ranging from 500–1000 mm yr−1, fallout records were generally satisfactory and it was possible to develop independent sediment chronologies based on the radiometric data alone. At the Egyptian sites, rainfall was less than 200 mm yr−1 and fallout records were much less distinct. At these sites the radiometric data could only be used to give an indication of mean sedimentation rates during the past 30–40 years. By using a combination of fallout radionuclide, pollen, and macrofossil stratigraphic records it was however possible to determine a credible sediment chronology spanning the major part of the 20th century. Applying this chronology to records of spheroidal carbonaceous particles (SCP) from the same sediment cores, the onset of significant levels of atmospheric pollution in the Nile Delta is dated in all three cores to the mid 1950s. Results from a number of lakes (Sidi Bou Rhaba, Ichkeul and Korba) revealed high and accelerating siltation rates, threatening their continued existence beyond the next few decades. In contrast, sedimentation rates at all three Nile Delta sites appear to have declined in recent decades, most probably due to the impact of the Nile barrages.

Factors Controlling the Holocene Avulsion History of the Rhine-Meuse Delta (The Netherlands)

ABSTRACT The avulsion history of the Holocene Rhine-Meuse delta (The Netherlands) was reconstructed, on a timescale of millenia, using detailed paleogeographic maps based on approximately 200,000 lithological borehole descriptions, over 1150 14C ages, and 36,000 archaeological artifacts. Gradient lines were constructed for all channel belts. These allowed determination of gradients, paleo-flow direction, relative age of channel belts, and time correlation of undated channel-belt fragments. Avulsion sites were inferred from the paleogeographic reconstruction. At least 91 avulsions occurred over the past 10,000 years, of which 82 could be dated with an accuracy of ± 200 14C years. The location and shifting of Holocene avulsion sites in the Rhine-Meuse delta in space and time are related to: (1) Relative sealevel rise. In the Early Holocene, avulsions could not take place, because rivers were still incised. Around 7500 yr BP, avulsions occurred in the western part of the present delta as a result of backfilling of the Late Weichselian valley. Between 7500 and 3700 yr BP, the zone where avulsions occurred shifted inland as a result of relative sealevel rise. (2) Neotectonics. Between 4900 and 1700 yr BP, the location of avulsion sites seems to have been influenced by neotectonic movements of the upthrown Peel Horst. Four out of six avulsion nodes in the Rhine-Meuse delta were located in the Peel Horst fault zones. (3) Increased discharge and/or within-channel sedimentation. From 2800 until about 1500 yr BP, avulsion sites were located all over the delta. During this time, the number of channels was high, and avulsion frequency reached a maximum, at a time when aggradation rate decreased with a reduction in the rate of sealevel rise. After 2000 yr BP meander wavelength of alluvial channels increased considerably. The increased meander wavelength and the high avulsion frequency are attributed to increased bankfull discharge or within-channel sedimentation (leading to channel widening), or both. (4) Human influence. Between 1000 and 650 yr BP, all the rivers were embanked, and avulsions could no longer take place. The few that occurred were induced by humans.

Deltas, radiocarbon dating, and measurements of sediment storage and subsidence

In Holocene marine deltaic sequences there is no simple relationship between radiocarbon age and depth of sampling. The Nile and Ganges-Brahmaputra deltas show remarkably similar radiocarbon age-depth relationships: (1) most radiocarbon dates, by conventional and accelerator mass spectrometric (AMS) analyses, are older (some by 4000 yr) than reasonably expected; (2) dates are commonly inverted (i.e., older upcore); and (3) sample dates at delta surfaces commonly exceed 2000 yr B.P. These anomalous age-depth phenomena are in part a response to reservoir effects, introduction of old carbon, and, emphasized herein, influence of sediment storage and remobilization that prevail in fluvial and delta plains. In fluvial systems, sediment generally is not transported in a single episode from its original source area to the sea. Rather, material transported from upland reaches and river valley to coast is subject to a repeated series of depositional, burial, and erosional events induced by episodic flooding, overbank sedimentation, and channel migration. Because sediment is likely to be temporarily stored in the delta plain, it is difficult to determine the time of a sediment9s final deposition and burial at a delta site. A successful strategy requires use of several independent dating methods, including AMS analyses of in situ basal peats and fossils and, where possible, archaeological evaluation of associated artifacts that are in place. Accurate dates are needed for reliable measurement of rates of delta plain aggradation and land subsidence, information to help implement effective coastal protection measures.

Pharmacology of [Tyr1]nociceptin analogs: receptor binding and bioassay studies.

Two series of nociceptin (NC)-related peptides with or without replacement of the N-terminal Phe by Tyr have been investigated in an attempt to obtain compounds that interact with the NC receptor (ORL1) and classic opioid receptors. When tested for their ability to displace [3H]NCNH2 ([3H]nociceptin amide; ORL1 sites) or the selective opioid receptor ligands [3H]DAMGO (mu), [3H]deltorphin II (delta) and [3H]U69593 (kappa) from their respective binding sites in guinea-pig brain membranes, [Tyr1]NCNH2 and [Tyr1]NC(1-13)NH2 showed high affinities (Ki 2nM and 5 nM, respectively) for ORL1 and approximately tenfold lower potency for mu (32nM and 44nM) and kappa sites (42 nM and 48 nM). They also interacted, but with low potency (Ki 410 nM and 310 nM) with delta sites. Shorter fragments as [Tyr1]NC(1-9)NH2 and [Tyr1]NC(1-5)NH2 were found to be inactive on ORL1, delta and kappa sites, and extremely weak (Ki 2224 nM and 4228 nM, respectively) on mu. Results of bioassays performed on the guinea-pig ileum (ORL1 and mu receptors), mouse vas deferens (ORL1 and delta receptors), and rabbit vas deferens (kappa receptor) confirmed (at least partially) the data of the binding by showing that [Tyr1]NC analogs interact with functional ORL1 as well as with classic opioid receptors. [Tyr1]NCNH2 and [Tyr1]NC(1-13)NH2 behaved as mixed ORL1/opioid receptor agonists showing similar affinities as the control NC sequence while [Tyr1]NC(1-9)NH2 and [Tyr1]NC(1-5)NH2 were inactive on ORL1 receptors but maintained some activities on opioid receptors: their effects were prevented by naloxone. The results of this study indicate that the replacement of Phe1 by Tyr in NC leads to compounds which bind both the ORL1 and mu/kappa receptors and may represent new promising agents for use in peripheral organs.

Environmental effects of growing woody crops on agricultural land: first year effects on erosion, and water quality

The objective of this study is to assess the effects of converting row crop agricultural land to short-rotation-woody-crops (SRWC) on erosion, surface water quantity and quality, and groundwater quality. Three physiographic regions in the Southeast, of varying soils, slope, and erodibility, were used. Replicate plots were equipped with a flume and four pan lysimeters so that event sampling of runoff and groundwater could be conducted. Cropping treatments had little effect on the runoff volumes collected; however, sediment produced by the various treatments was significantly influenced by crop. At all three sites, spring and fall generally had the highest sediment losses. The highest absolute losses of sediment occurred at the Mississippi Delta site. Conventional tilled cotton ( Gossypium hirsutum L.) lost 16.2 Mg ha −1, compared to 2.3 Mg ha −1 for cottonwood ( Populus deltoides Marsh) over 14 months. While sediment losses at a loess-belt site in west Tennessee were three-fold higher under no-till corn ( Zea maize L.) than sycamore ( Platinus occidentalis L), total sediment loss was less than 1 Mg ha −1 for both treatments. At the north Alabama site, no-till corn and sweetgum ( Liquidambar styraciflua L.) with a fescue ( Fescue elitor L.) cover crop did not differ with respect to erosion. However, sediment losses under sweetgum without a cover crop were significantly higher, exceeding 5 Mg ha −1. Nutrient losses of N and P in both runoff and lysimeters were primarily influenced by spring mineral fertilizer applications. Spring and early summer lysimeter nitrate values exceeded EPA guideline for drinking water in the row crop treatments.

Developmental and regional alteration of kappa-opioid receptors in seizure-susceptible EL mouse brain.

The binding of [3H]ethylketocyclazocine ([3H]EKC) under the suppression of mu and delta sites in the brain of EL mice (seizure-susceptible) was examined to determine the relationship between seizures and the dynorphinergic system. The density of kappa-opioid receptors in the cerebrum of adult EL mice during interictal periods significantly increased, without changes in apparent affinities, compared with that of adult ddY mice (seizure-nonsusceptible; the mother strain of EL). Subsequently, the binding of 0.8 nM [3H]EKC in 8 brain regions was examined in the 2 strains. The [3H]EKC binding in 25-day-old EL mice that had no seizures significantly increased in the hippocampus and amygdala. At the age of 50 days, EL mice displayed abortive seizures, and the number of kappa sites in EL mice was significantly greater in the hippocampus, amygdala and cerebral cortex. It was further shown that the binding of [3H]EKC in 150-day-old adult EL mice during interictal periods was markedly increased in the hippocampus, amygdala, cerebral cortex and striatum, compared with the corresponding regions in ddY mice. The up-regulation of kappa receptors in the EL mouse brain may result from deficits in endogenous dynorphins, which could be involved in the pathogenesis of seizure diathesis and seizure manifestations in the EL mouse.

Soil response on the Fraser delta to theMW= 5.1 Duvall, Washington, earthquake

AbstractStrong-motion recordings of the 3 May 1996 MW = 5.1 Duvall, Washington, earthquake made in southwestern British Columbia provide the best constraints, to date, on soil response to seismic shaking on the Fraser delta, just south of Vancouver. A total of nine strong-motion instruments in southern B.C. triggered during this earthquake, seven of which are on or near the Fraser delta. These recordings were made at epicentral distances of 140 to 180 km. A preliminary analysis of these data clearly shows that for low frequencies (<3 Hz) seismic spectral amplification (by a factor of 2 to 7) occurs on the Fraser delta relative to nearby bedrock or thin firm-soil sites. However, at higher frequencies, moderate attenuation is observed at the Fraser delta sites. The largest peak ground accelerations recorded (generally around 2 to 3 Hz) were not on the thickest delta sediments but nearer the edge of the delta. Peak amplification is more pronounced in the horizontal component of ground motion than in the vertical. The average SH/Z ratio for peak values at the Fraser delta sites is 4.5 ± 0.9 compared to 1.6 ± 0.6 for the bedrock and firm-soil sites. In addition to the strong-motion records, we also utilize five three-component broadband recordings of this earthquake made in southern B.C. (epicentral distances of 140 to 520 km), and 12 short-period vertical-component recordings (epicentral distances of 130 to 380 km) to document attenuation of peak acceleration with distance for this earthquake. The observed values are slightly lower than those predicted by the ground-motion relations proposed for the year 2000 National Building Code of Canada.

Affinity labelling of frog brain opioid receptors by dynorphin(1-10) chloromethyl ketone.

It has been previously found that chloromethyl ketone derivatives of enkephalins bind irreversibly to the opioid receptors in vitro. Recently a novel affinity reagent, Tyr-Gly-Gly-Phe-Leu-Arg-Arg-Ile-Arg-Pro-Gly chloromethyl ketone (Dynorphin(1-10)-Gly11 chloromethyl ketone, DynCMK) was synthesized, and its binding characteristics to frog (Rana esculenta) brain membranes were evaluated. In competition experiments, the product shows a relatively high affinity for the kappa-opioid binding sites labelled by [3H]ethylketocyclazocine (Ki is approximately equal to 200 nM), whereas its binding to the 1 ([3H]dihydromorphine) and to the delta sites ([3H]D-Ala2-Leu5]enkephalin) is weaker. Preincubation of the frog brain membranes with DynCMK at micromolar concentrations results in a washing-resistant and dose-dependent inhibition of the [3H]ethylketocyclazocine binding sites. Saturation binding analysis of the membranes preincubated with 50 microM DynCMK reveals a significant decrease in the number of specific binding sites for [3H]ethylketocyclazocine compared to the control values. The kappa-preferring binding properties of the compound suggest that it could serve as an affinity label for the kappa-type of opioid receptors.

Radon levels measured at building sites and in sub-soil in Delta

The concentration of radon in the open air and interiors and in sub-soil of Delta sites was determined by using solid state nuclear track detectors (SSNTDs). Radon concentration measurements in air in Delta, north Cairo, were performed by open and filtered detectors, with small volume and CR-39 plastic film. The equilibrium factor F and the dose equivalent were calculated by using the track densities of open and filtered SSNTDs.

Tales of a Delta Site: The 1995 Field Season at Tell el-Muqdam

Tales of a Delta Site: The 1995 Field Season at Tell el-Muqdam

Portacaval anastomosis induces region-selective alterations of the endogenous opioid system in the rat brain.

Portacaval anastomosis (PCA) in the rat results in a broad spectrum of neurological and neurobehavioral changes, including alterations of circadian rhythms, impaired locomotor activity, and reflexes, as well as decreased threshold to noxious stimuli. In addition, following portacaval shunting, rats drink significantly more ethanol in a free-choice drinking paradigm. Available evidence suggests that many of these behavioral changes may be modulated by the endogenous opioid system of the brain. To evaluate this possibility, the effects of PCA on circulating beta-endorphin (beta-EP), as well as beta-EP content in the pituitary and specific brain nuclei, was evaluated using a sensitive radioimmunoassay. Furthermore, the characteristics and regional densities of mu and delta opioid receptors in the brains of PCA and sham-operated control rats were studied using an in vitro technique, as well as quantitative receptor autoradiography and the specific ligands 125I [D-Ala2, MePhe4, Met(o)ol5]enkephalin (FK 33-824) and 125I [2-D-penicillamine, 5-D-penicillamine]-enkephalin (DPDPE) for micro and delta sites, respectively. PCA resulted in region-selective modifications of beta-EP in brain, but not in pituitary or blood. Autoradiographic studies revealed a generalized decrease in mu binding sites (up to 70% decreases compared with sham-operated controls) and region-selective alterations of delta receptor densities following PCA. Portacaval-shunted rats drank significantly more ethanol in a free-choice drinking paradigm, an effect that was significantly attenuated by the administration of the opiate antagonist naloxone. Increased ethanol preference thus appeared to result from modifications of the endogenous opioid system in nucleus accumbens of rats following PCA.

Portacaval anastomosis induces region-selective alterations of the endogenous opioid system in the rat brain

Portacaval anastomosis (PCA) in the rat results in a broad spectrum of neurological and neurobehavioral changes, including alterations of circadian rhythms, impaired locomotor activity, and reflexes, as well as decreased threshold to noxious stimuli. In addition, following portacaval shunting, rats drink significantly more ethanol in a free- choice drinking paradigm. Available evidence suggests that many of these behavioral changes may be modulated by the endogenous opioid system of the brain. To evaluate this possibility, the effects of PCA on circulating beta-endorphin (beta-EP), as well as beta-EP content in the pituitary and specific brain nuclei, was evaluated using a sensitive radioimmunoassay. Furthermore, the characteristics and regional densities of mu and delta opioid receptors in the brains of PCA and sham-operated control rats were studied using an in vitro technique, as well as quantitative receptor autoradiography and the specific ligands 125I [D-Ala2, MePhe4, Met(o)ol5]enkephalin (FK 33-824) and 125I [2-D-penicillamine, 5-D-penicillamine]-enkephalin (DPDPE) for micro and delta sites, respectively. PCA resulted in region-selective modifications of beta-EP in brain, but not in pituitary or blood. Autoradiographic studies revealed a generalized decrease in mu binding sites (up to 70% decreases compared with sham-operated controls) and region-selective alterations of delta receptor densities following PCA. Portacaval-shunted rats drank significantly more ethanol in a free- choice drinking paradigm, an effect that was significantly attenuated by the administration of the opiate antagonist naloxone. Increased ethanol preference thus appeared to result from modifications of the endogenous opioid system in nucleus accumbens of rats following PCA. (Hepatology 1996 Oct;24(4):895-901)

Synthesis and characterization of substituted benzoylhydrazones of naloxone

Naloxone benzoylhydrazone (NalBzoH) has proved a valuable tool in the investigation of opioid receptor subtypes. In the present study, we have examined a series of derivatives of NalBzoH in which substitutions have been made on the benzoyl ring. Overall, we see dramatic effects on the binding affinities of derivatives against the various opioid receptor subtypes. Although the range of affinities against the mu receptors is quite modest, ranges of the others vary almost 30-fold for kappa 3, 50-fold for kappa 1 and 100-fold for delta and kappa 2 binding. Few substituted derivatives display greater affinity than NalBzoH for any of the receptors, except for delta sites where several derivatives have affinities almost tenfold greater than NalBzoH. Along with the wide variations in affinity, the compounds also appear to exhibited widely divergent activities in traditional bioassays.

Binding sites contribute unequally to the gating of mouse nicotinic alpha D200N acetylcholine receptors.

1. Single channel currents were recorded from HEK 293 cells expressing recombinant mouse adult (alpha 2 beta delta gamma) acetylcholine receptors (AChRs) containing a mutation at residue D200 of the alpha-subunit. Rate and equilibrium constants for AChR activation were estimated from open and closed time obtained over a range of ACh concentrations. 2. Mutation of alpha D200 to asparagine (alpha D200N) dramatically slows the rate constant of channel opening, with adult AChRs slowing 100-fold and embryonic AChRs slowing 400-fold. the rate constant of channel closing increased 3-fold, resulting in a decrease of the gating equilibrium constant of up to 1200-fold. In contrast to channel gating steps, ACh-binding steps are only modestly effected by alpha D200N. 3. Introduction of a potential glycosylation site in alpha D200N cannot account for the effect on channel gating because eliminating the consensus for glycosylation with the mutation alpha D200N + T202V fails to restore efficient gating. Gating is similarly impaired with the substitutions of E, K and Q at position alpha 200. 4. the agonists carbamylcholine and tetramethylammonium also activate the alpha D200N AChR, but with channel opening rates even slower than with ACh. The agonist dependence of the opening rate constant is similar in alpha D200N and wild type AChRs. 5. AChRs containing D200N at just one of the two alpha-subunits show either small or large changes in the gating equilibrium constant, presumably due to the presence of the mutation at either the alpha delta or alpha epsilon/alpha gamma sites. The changes in free energy of channel gating show that the contribution of each binding site is nearly independent. However, the sites do not contribute equally to gating, as an alpha D200N mutation at the alpha epsilon or alpha gamma binding site slows channel opening relatively more than at the alpha delta site.

Activation of the CPP32 Protease in Apoptosis Induced by 1-β-D-Arabinofuranosylcytosine and Other DNA-Damaging Agents

The response of human myeloid leukemia cells to treatment with 1-beta-arabinofuranosylcytosine (ara-C) includes the induction of apoptosis. Ara-C induced apoptosis is associated with proteolytic cleavage of poly(ADP-ribose) polymerase (PARP) and protein kinase C (PKC) delta. However, the signals involved in this response are unknown. The present studies show that ara-C treatment of U-937 cells is associated with induction of a protease activity that cleaves the tetrapeptides Ac-DEVD-pNA and Ac-DMOD-pNA found at the cleavage sites of PARP and PKC delta, respectively. The ara-C-induced protease activity was sensitive to overexpression of the anti-apoptotic protein Bcl-xL and the baculovirus protein p35. By contrast, overexpression of the cowpox virus protein CrmA blocked apoptosis induced by engagement of the Fas receptor but not that induced by ara-C. CrmA overexpression also had no detectable effect on ara-C-induced cleavage of PKC delta. The results further show that ara-C induces activation of the CPP32 protease by a CrmA-insensitive and p35-sensitive mechanism. Similar results were obtained with cisplatinum, etoposide, and camptothecin. These findings indicate that ara-C and other DNA-damaging agents activate a CrmA-insensitive apoptotic pathway involving CPP32 and that these signals differ from those associated with apoptosis induced by the Fas receptor.

Pitch Pine (Pinus rigida Mill.) Communities in the Hudson Valley Region of New York

This study is part of a coordinated series to describe the pine barrens of New York, communities characteristic of disturbed sites with poor soils. Pitch pine (Pinus rigida Mill.) communities in the Hudson Valley region of New York were found on a sand dune, alluvium, a lacustrine delta and on conglomerate and sandstone outcrops. The alluvium and lacustrine delta sites supported more mesic communities with higher tree and herb species richness than the sand dune site, but lacked a shrub layer. The sand dune, sandstone outcrop and conglomerate sites supported open tree canopy communities in which ericaceous shrubs, especially Gaylussacia baccata, dominated a distinct shrub layer. Community types could be classified into three physiognomic forms. Probably the most disturbed were communities of dwarf vegetation dominated by either pitch pine or scrub oak (Quercus iliczfolia). A second type was characterized by an open canopy of short pitch pines with an extensive shrub layer of scrub oaks or ericaceous shrubs. The third type had a closed canopy of tall pitch pine, red maple (Acer rubrum), red oak (Q. rubra) and/or white oak (Q alba), few shrubs but a considerable number of forest floor herbaceous species. The southeastern area is of particular interest because two of the best known pine barrens in New York, the Albany Pine Bush and the Schawangunk Mountains dwarf forest are lo- cated there. The Pine Bush has been the subject of a number of publications, most ad- dressed to a general audience (Rittner, 1975, for example), but Milne (1985) made a de- tailed study of upland forests and their successional development. He suggested that areas dominated by scrub oak (Quercus ilicifolia) with scattered pitch pine were characteristic of very disturbed sites, especially those that burned often. In the absence of disturbance, Milne believed they would succeed to closed-canopy pitch pine forests, then to areas dominated by a mixture of pitch pine, white pine (Pinus strobus), red oak (Quercus rubra), white oak (Q alba), red maple (Acer rubrum) and white ash (Fraxinus americana). Schawangunk Mountain ridge vegetation was described by McIntosh (1959), who noted that bare rock surfaces of the ridges were covered with pitch pine, sometimes dwarfed, no more than 1-3 m tall. These dwarf ridge top communities graded into taller pitch pine and