The design and pharmacology of novel selective muscarinic agonists and antagonists

The muscarinic pharmacology of C1-methyl-substituted chiral compounds related to McN-A-343 and of (R)- and (S)-dimethindene has been studied. Among the McN-A-343 analogues, the (S)-enantiomers were more potent and had higher affinity than the (R)-isomers. The quaternary compound (S)-BN 228 was found to be the most potent M1-selective agonist known today (pEC50: M1/rabbit vas deferens = 7.83; M2/guinea-pig atria = 6.35; M3/guinea-pig ileum = 6.29). In both the atria and ileum the tertiary carbamate, (S)-4-F-MePyMcN, was a competitive antagonist (pA2 value = 7.39 and 6.82, respectively). In contrast, in rabbit vas deferens (S)-4-F-MePyMcN was a potent partial agonist (pEC50 = 7.22; apparent efficacy = 0.83). These results indicate that (S)-4-F-MePyMcN might be a useful tool to study M1 receptor-mediated effects involved in central cholinergic function. (S)-Dimethindene was a potent M2-selective antagonist (pA2 = 7.86/atria; pKi = 7.8/rat heart) with lower affinities for the M1 (pA2 = 6.36/rat duodenum; pKi = 7.1/NB-OK 1 cells), M3 (pA2 = 6.92/guinea-pig ileum; pKi = 6.7/rat pancreas) and M4 receptors (pKi = 7.0/rat striatum). It was more potent (up to 41-fold) than the (R)-isomer. In contrast, the stereoselectivity was inverse at ileal H1 receptors (pA2: (R)-isomer = 9.42; (S)-isomer = 7.48). Thus, (S)-dimethindene could be a valuable agent to test the hypothesis that M2 antagonists show beneficial effects in the treatment of cognitive disorders. It might also become the starting point for the development of diagnostic tools for quantifying M2 receptors in the CNS with PET imaging.     

Biomass,composition and activity of organism assemblages along a salinity gradient in sea ice subjected to river discharge in the Baltic Sea

A study was undertaken to examine the activity and composition of the seasonal Baltic Sea land-fast sea-ice biota along a salinity gradient in March 2003 in a coastal location in the SW coast of Finland. Using a multi-variable data set, the less well-known algal and protozoan communities, and algal and bacterial production in relation to the physical and chemical environment were investigated. Also, the first coincident measurements of bacterial production and dissolved organic matter (DOM) in a sea-ice system are reported. Communities in sea ice were clearly autotrophy-dominated with algal biomass representing 79% of the total biomass. Protozoa and rotifers made up 18% of biomass in the ice and bacteria only 3%. Highest biomasses were found in mid-transect bottom ice. Water column assemblages were clearly more heterotrophic: 39% algae, 12% bacteria and 49% for rotifers and protozoa. Few significant correlations existed between DOM and bacterial variables, reflecting the complex origin of ice DOM. Dynamics of dissolved organic carbon, nitrogen and phosphorus (DOC, DON and DOP) were also uncoupled. A functional microbial loop is likely to be present in the studied ice. Existence of an under-ice freshwater plume affects the ecosystem functioning: Under-ice water communities are influenced directly by river-water mixing, whereas the ice system seems to be more independent—the interaction mainly taking place through the formation of active bottom communities.     

Scales of horizontal patchiness in chlorophyll a, chemical and physical properties of landfast sea ice in the Gulf of Finland (Baltic Sea)

Horizontal variation of first-year landfast sea ice properties was studied in the Gulf of Finland, the Baltic Sea. Several scales of variation were considered; a number of arrays with core spacings of 0.2, 2 and 20 m were sampled at different stages of the ice season for small-scale patchiness. Spacing between these arrays was from hundreds of meters to kilometers to study mesoscale variability, and once an onshore–offshore 40-km transect was sampled to study regional scale variability. Measured variables included salinity, stable oxygen isotopes (¹⁸O), chlorophyll a (chl-a), nutrients and dissolved organic carbon. On a large scale, a combination of variations in the under-ice water salinity (ice porosity), nutrient supply and the stage of ice development control the build-up of ice algal biomass. At scales of hundreds of meters to kilometers, there was significant variability in several parameters (salinity, chl-a, snow depth and ice thickness). Analyses of the data from the arrays did not show evidence of significant patchiness at scales <20 m for algal biomass. The results imply that the sampling effort in Baltic Sea ice studies should be concentrated on scales of hundreds of meters to kilometers. Using the variations observed in the study area, the estimate for depth-integrated algal biomass in landfast sea ice in the Gulf of Finland (March 2003) is 5.5±4.4 mg chl-a m^–2.     

Sea ice bacterial growth rate, growth efficiency and preference for inorganic nitrogen sources in the Baltic Sea

Seasonal Baltic Sea ice is structurally similar to polar sea ice and provides habitats for diverse ice organism assemblages that are integral to the biogeochemistry and ecology of the sea during winter. Temperature and inorganic nitrogen sources have been suggested to control bacterial growth, with increasing dependence on ammonium at low temperatures. To study the bacterial growth and preference for the nitrogen source, we conducted experiments at 0 and 4°C, using ammonium and nitrate as nitrogen sources at two coastal fast-ice stations in the Gulf of Finland and in the Gulf of Bothnia during three successive winters. The two study sites differ markedly in relation to the allochthonous dissolved organic matter supply from the catchment area. High levels of bacterial growth were recorded at both study sites, with community generation times of 15–37 h. The measured bacterial growth efficiencies of 20–58% suggest that the Baltic sea ice brines provide a rich medium for bacterial growth and efficient functioning of bacteria-based food webs. Our experiments with sea ice samples showed a preference for ammonium at both temperatures and high potential growth in both types of nitrogen supplies. No major differences in phosphorus depletion rates were found at the two temperatures, but rates were always highest when ammonium was added to the experiments. These experiments point out that ice maturity, presumably through changes in bacterial community structure, impacts nitrogen processes and that these processes are pronounced prior to melting of the ice.     

Responses of Baltic Sea ice and open-water natural bacterial communities to salinity change

To investigate the responses of Baltic Sea wintertime bacterial communities to changing salinity (5 to 26 practical salinity units), an experimental study was conducted. Bacterial communities of Baltic seawater and sea ice from a coastal site in southwest Finland were used in two batch culture experiments run for 17 or 18 days at 0 degrees C. Bacterial abundance, cell volume, and leucine and thymidine incorporation were measured during the experiments. The bacterial community structure was assessed using denaturing gradient gel electrophoresis (DGGE) of PCR-amplified partial 16S rRNA genes with sequencing of DGGE bands from initial communities and communities of day 10 or 13 of the experiment. The sea ice-derived bacterial community was metabolically more active than the open-water community at the start of the experiment. Ice-derived bacterial communities were able to adapt to salinity change with smaller effects on physiology and community structure, whereas in the open-water bacterial communities, the bacterial cell volume evolution, bacterial abundance, and community structure responses indicated the presence of salinity stress. The closest relatives for all eight partial 16S rRNA gene sequences obtained were either organisms found in polar sea ice and other cold habitats or those found in summertime Baltic seawater. All sequences except one were associated with the alpha- and gamma-proteobacteria or the Cytophaga-Flavobacterium-Bacteroides group. The overall physiological and community structure responses were parallel in ice-derived and open-water bacterial assemblages, which points to a linkage between community structure and physiology. These results support previous assumptions of the role of salinity fluctuation as a major selective factor shaping the sea ice bacterial community structure.     

The northern Baltic Sea phytoplankton communities in 1903–1911 and 1993–2005: a comparison of historical and modern species data

Despite over 100 years of phytoplankton research in the Baltic Sea, little is known about how the species composition has changed during this period, characterised by severe anthropogenic eutrophication. We investigated the phytoplankton communities in the northern Baltic Sea using data from 1903 to 1911 and 1993 to 2005; to minimise effects of methodological differences we focused on occurrence frequencies. We found that the historical and modern communities differed regarding both species composition and the relative importance of taxonomical groups. The most obvious differences were the increase of dinoflagellates and decrease in the diatom to dinoflagellate ratio in all seasons. Contrary to the widely held view that cyanophytes have gained significance, our results indicate that in terms of occurrence the group has not increased in summer, and has lost ground in both spring and autumn. Several shifts in the occurrence frequency and seasonality of individual taxa transpired. Examining our results in relation to environmental conditions we found that some changes may be symptomatic of climate change related pressures. However, statistical analyses revealed that an undefined ‘period effect’ was the most important factor separating the historical and modern phytoplankton communities. We interpret this ‘period effect’ as evidence for the direct and/or indirect influence of eutrophication.     

The relative contributions of biological and abiotic processes to carbon dynamics in subarctic sea ice

Knowledge on the relative effects of biological activity and precipitation/dissolution of calcium carbonate (CaCO₃) in influencing the air-ice CO₂ exchange in sea-ice-covered season is currently lacking. Furthermore, the spatial and temporal occurrence of CaCO₃ and other biogeochemical parameters in sea ice are still not well described. Here we investigated autotrophic and heterotrophic activity as well as the precipitation/dissolution of CaCO₃ in subarctic sea ice in South West Greenland. Integrated over the entire ice season (71 days), the sea ice was net autotrophic with a net carbon fixation of 56 mg C m^?2, derived from a sea-ice-related gross primary production of 153 mg C m^?2 and a bacterial carbon demand of 97 mg C m^?2. Primary production contributed only marginally to the TCO₂ depletion of the sea ice (7–25 %), which was mainly controlled by physical export by brine drainage and CaCO₃ precipitation. The net biological production could only explain 4 % of this sea-ice-driven CO₂ uptake. Abiotic processes contributed to an air-sea CO₂ uptake of 1.5 mmol m^?2 sea ice day^?1, and dissolution of CaCO₃ increased the air-sea CO₂ uptake by 36 % compared to a theoretical estimate of melting CaCO₃-free sea ice. There was a considerable spatial and temporal variability of CaCO₃ and the other biogeochemical parameters measured (dissolved organic and inorganic nutrients).     

Isolation and characterization of phage–host systems from the Baltic Sea ice

In search for sea ice bacteria and their phages from the Baltic Sea ice, two ice samples were collected from land-fast ice in a south-west Finland coastal site in February and March 2011. Bacteria were isolated from the melted sea ice samples and phages were screened from the same samples for 43 purified isolates. Plaque-producing phages were found for 15 bacterial isolates at 3 °C. Ten phage isolates were successfully plaque purified and eight of them were chosen for particle purification to analyze their morphology and structural proteins. Phage 1/32 infecting an isolate affiliated to phylum Bacteroidetes (Flavobacterium sp.) is a siphovirus and six phages infecting isolates affiliated to γ-Proteobacteria (Shewanella sp.) hosts were myoviruses. Cross titrations between the hosts showed that all studied phages are host specific. Phage solutions, host growth and phage infection were tested in different temperatures revealing phage temperature tolerance up to 45 °C, whereas phage infection was in most of the cases retarded above 15 °C. This study is the first to report isolation and cultivation of ice bacteria and cold-active phages from the Baltic Sea ice.     

Responses of Baltic Sea Ice and Open-Water Natural Bacterial Communities to Salinity Change

To investigate the responses of Baltic Sea wintertime bacterial communities to changing salinity (5 to 26 practical salinity units), an experimental study was conducted. Bacterial communities of Baltic seawater and sea ice from a coastal site in southwest Finland were used in two batch culture experiments run for 17 or 18 days at 0°C. Bacterial abundance, cell volume, and leucine and thymidine incorporation were measured during the experiments. The bacterial community structure was assessed using denaturing gradient gel electrophoresis (DGGE) of PCR-amplified partial 16S rRNA genes with sequencing of DGGE bands from initial communities and communities of day 10 or 13 of the experiment. The sea ice-derived bacterial community was metabolically more active than the open-water community at the start of the experiment. Ice-derived bacterial communities were able to adapt to salinity change with smaller effects on physiology and community structure, whereas in the open-water bacterial communities, the bacterial cell volume evolution, bacterial abundance, and community structure responses indicated the presence of salinity stress. The closest relatives for all eight partial 16S rRNA gene sequences obtained were either organisms found in polar sea ice and other cold habitats or those found in summertime Baltic seawater. All sequences except one were associated with the α- and γ-proteobacteria or the Cytophaga-Flavobacterium-Bacteroides group. The overall physiological and community structure responses were parallel in ice-derived and open-water bacterial assemblages, which points to a linkage between community structure and physiology. These results support previous assumptions of the role of salinity fluctuation as a major selective factor shaping the sea ice bacterial community structure.