Opioid receptor antagonist affinity ligands: 6β-bromoacetamido-6-desoxynaltrexone and 6β-thioglycolamido-6-desoxynaltrexone

The present study, utilizing thioglycolamido as the reactive group, describes the synthesis and pharmacology of a new opioid antagonist affinity ligand, 6-thioglycolamido-6-desoxynaltrexone (TAN) and compares TAN with a related known compound, 6-bromoacetamido-6-desoxynaltrexone (BAN). Both compounds were tested for their reversible and irreversible inhibition of [³H]naloxone binding to calf brain membranes. Reversible binding of BAN and TAN had K_i values of 1×10^–9 and 1×10^–10 M, respectively as determined by log probit plots. Irreversible binding was determined after extensive washing to remove all non-covalently bound ligand. At a concentration of 5×10^–8 and 1×10^–8 M for BAN and TAN irreversible binding was inhibited 50% of the maximum value. A study of the time course of irreversible inhibition of [³H]naloxone binding revealed that maximal inhibition occurred within 5 min with a concentration of 1×10^–7 M of either agent. TAN but not BAN when administered systematically to mice produced an antinociceptive effect as measured by the writhing test. When administered intracerebraventricularly BAN did not block morphine-induced analgesia for more than 2 hr; whereas, with a single ED₅₀ dose of 20 nmoles of TAN i.c.v. morphine-induced analgesia was almost completely blocked for a period of over 24 hr, as determined by the tail flick test. Although the SH group of TAN were required for the covalent interaction with opioid receptors, the site of TAN's interaction appears to involve other than protein SH groups.     

Purification of the bovine rod outer segment Na+/Ca2+ exchanger

Optimal conditions for solubilization and stabilization of the Na+/Ca2+ exchanger from rod outer segments were examined. The exchanger was found to be most stable at low detergent concentrations (7.5 mM 3-[(3-cholamidopropyl)dimethylammonio]-1-propane-sulfonate), greater than or equal to 100 mM NaCl, pH 7.0-7.5, and with 0.1% added soybean asolectin. The sulfhydryl-modifying reagent, dithiothreitol, caused a loss of exchanger activity and was omitted throughout the purification procedure. These conditions were used to purify the Na+/Ca2+ exchanger from rod outer segments by a combination of selective solubilization, ion exchange, and wheat germ agglutinin chromatography. The procedure achieves a 336-fold increase in exchanger specific activity. The presence of exchanger activity most closely correlates with a polypeptide of molecular mass 215-kDa. Exchanger activity in both the crude rod outer segments and the purified exchanger is specifically dependent upon the presence of K+ in the assay medium; neither choline nor Li+ can substitute for K+.     

Identification of a peptide inhibitor of the cardiac sarcolemmal Na(+)-Ca2+ exchanger

The deduced amino acid sequence of the cardiac sarcolemmal Na(+)-Ca2+ exchanger has a region which could represent a calmodulin binding site. As calmodulin binding regions of proteins often have an autoinhibitory role, a synthetic peptide with this sequence was tested for functional effects on Na(+)-Ca2+ exchange activity. The peptide inhibits the Na(+)-dependent Ca2+ uptake (KI approximately 1.5 microM) and the Nao(+)-dependent Ca2+ efflux of sarcolemmal vesicles in a noncompetitive manner with respect to both Na+ and Ca2+. The peptide is also a potent inhibitor (KI approximately 0.1 microM) of the Na(+)-Ca2+ exchange current of excised sarcolemmal patches. The binding site for the peptide on the exchanger is on the cytoplasmic surface of the membrane. The exchanger inhibitory peptide binds calmodulin with a moderately high affinity. From the characteristics of the inhibition of the exchange of sarcolemmal vesicles, we deduce that only inside-out sarcolemmal vesicles participate in the usual Na(+)-Ca2+ exchange assay. This contrasts with the common assumption that both inside-out and right-side-out vesicles exhibit exchange activity.     

Studies in the bivalve, Tellina tenuis Da Costa. IV. Further experiments in enriched sea water

Tellina tennis Da Costa was kept for four months in four large outdoor tanks containing sand and sea water. There was a 10 % daily exchange of sea water, pumped directly from the sea. Three tanks received daily addition of nutrients in the form of sodium nitrate and sodium dihydrogen phosphate, giving enrichment of approximately 3, 10, and 30 times natural sea-water levels of nitrate in the different tanks. Phosphate, nitrate, chlorophyll, and organic carbon in the water were measured regularly, the nitrate by Autoanalyser. Water temperature and solar radiation were recorded. Zooplankton samples were taken daily and Tellina were sampled monthly for length, weight, and biochemical analysis of tissues.Phosphate was always present in excess. The lowest level of nitrogen enrichment resulted in almost complete utilisation of nitrate, with a significant increase of organic carbon and chlorophyll above control levels. Zooplankton occurred in the greatest numbers in this tank, and Tellina showed the best survival, growth, and condition. In the tanks with the higher levels of enrichment, excess nutrients led to growth of macrophytic algae on the surface and sides of tank. This had an adverse effect on the phytoplankton production: zooplankton numbers were lower, as was growth of Tellina.     

The short‐ and long‐term fitness consequences of natal dispersal in a wild bird population

Dispersal is a key process in population and evolutionary ecology. Individual decisions are affected by fitness consequences of dispersal, but these are difficult to measure in wild populations. A long‐term dataset on a geographically closed bird population, the Mauritius kestrel, offers a rare opportunity to explore fitness consequences. Females dispersed further when the availability of local breeding sites was limited, whereas male dispersal correlated with phenotypic traits. Female but not male fitness was lower when they dispersed longer distances compared to settling close to home. These results suggest a cost of dispersal in females. We found evidence of both short‐ and long‐term fitness consequences of natal dispersal in females, including reduced fecundity in early life and more rapid aging in later life. Taken together, our results indicate that dispersal in early life might shape life history strategies in wild populations.     

Numbers,migration phenology and survival of Purple Sandpipers Calidris maritima at Gourdon,eastern Scotland

Purple Sandpipers wintering on the Kincardine coast had a protracted autumn arrival (one-quarter and three-quarters of the birds arrived on 30 July and 21 October respectively, 83 days) but a faster spring departure (one-quarter and three-quarters departed on 9 April and 27 May respectively, 48 days). The long arrival period was partly due to differences in the migration phenology of the two main wintering populations: short-billed birds from Norway arrived before the long-billed birds, probably from Canada. There was a smaller difference in departure times of the two populations: short-billed birds left before the long-billed birds. Minimum annual survival was estimated from resightings of 92 marked birds. There was no evidence that survival differed between adults and first-years or between birds of different bill-size classes, which were of different sex and geographical origin. Minimum annual survival was estimated to be 79.5%(se = 2.8%). The similarity between the mortality rate (20.5%) and the percentage of first-year birds in populations of Purple Sandpipers probably reflects balanced population dynamics.     

Silent glutamatergic synapses in the mammalian brain

Excitatory synaptic transmission in the mammalian brain is mediated primarily by alpha-amino-3-hydroxy-5-methylisoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptors that are thought to be co-localized at individual synapses. However, recent electrophysiological and anatomical data suggest that the synaptic localization of AMPA and NMDA receptors may be independently regulated by neural activity. These data are reviewed here and the implications of these findings for the mechanisms underlying synaptic plasticity are discussed.     

Cartilage interstitial fluid load support in unconfined compression following enzymatic digestion

Interstitial fluid pressurization plays an important role in cartilage biomechanics and is believed to be a primary mechanism of load support in synovial joints. The objective of this study was to investigate the effects of enzymatic degradation on the interstitial fluid load support mechanism of articular cartilage in unconfined compression. Thirty-seven immature bovine cartilage plugs were tested in unconfined compression before and after enzymatic digestion. The peak fluid load support decreased significantly (p < 0.0001) from 84 +/- 10% to 53 +/- 19% and from 80 +/- 10% to 46 +/- 21% after 18-hours digestion with 1.0 u/mg-wet-weight and 0.7 u/mg-wet-weight of collagenase, respectively. Treatment with 0.1 u/ml of chondroitinase ABC for 24 hours also significantly reduced the peak fluid load support from 83 +/- 12% to 48 +/- 16% (p < 0.0001). The drop in interstitial fluid load support following enzymatic treatment is believed to result from a decrease in the ratio of tensile to compressive moduli of the solid matrix.