No description available.

No description available.

Members of voltage-gated potassium channel subfamily 3 (Kv3) have been extensively demonstrated to play a significant role in facilitating function of "fast-firing" neurons in the central nervous system. Kv3.1 and Kv3.3 channels, members of Kv3 channel subfamily, have different distribution profiles on the regional level of brain and on the subcellular level of neurons in mammals and in weakly electric fish, according to mRNA hybridizations in situ and immunohistochemical analysis. In mammals, Kv3.1 channels are expressed in soma, axon and proximal dendrites as well as presynaptic membrane of "fast-firing" neurons. In weakly electric fish (Apteronotus), Kv3.1 channels are distributed in the soma, in the basilar dendrites and in the proximal apical dendrites of pyramidal neurons; on the other hand, Kv3.3 channels are expressed in a larger region: soma, basilar dendrites and entire apical dendrites of these cells. Mechanisms underlying differential subcellular distribution of Kv3.1 and Kv3.3 channels in the apical dendritic compartment of pyramidal neurons are unknown. In order to identify peptide sequences responsible for the differential subcellular localization, I have used Semliki Forest virus as a modified viral expression system (PDE) in vivo to study dendritic targeting mechanisms in the pyramidal neurons of electrosensory lateral line lobe (ELL), where the primary processing for afferent input occurs in the apteronotid electrosensory system.

The response of in vitro-grown Solanum tuberosum L., cvs. Russet Burbank (RB) (salt-sensitive) and Sierra (S) (salt-tolerant) potatoes was investigated when [NaCl] was increased from 0 to 80 mM in the presence of 6, 20, and 30 mM [K] in a Murashige and Skoog (MS) basal medium. The tested growth parameters, Mg and Ca content, and K+/Na + ratios in the laminae and the roots were negatively affected as [NaCl] increased. The salt stress was relatively severe on growth of RB plants whereas the salt-tolerant (S) variety was affected to a lesser extent. There were indications that Na in the plant may promote Na translocation. In both cultivars, 22Na was not distributed equally in all plant parts; the lower lamina accumulated the highest amount (216 and 183 DPM mg -1 FW) followed by stem (197 and 182), petioles (187 and 168), and the upper lamina (149 and 121) for RB and S, respectively. / The salt resistance of S is associated not only with a superior capacity to accumulate high Na+ in the roots for osmotic adjustment, but also with resistance to Na movement to the shoot. / The effect of [K] on plant growth showed two main characteristics. In non-saline media, increasing [K] enhanced growth of S, while RB showed optimum growth when the normal (20 mM) level was present in the MS medium. In saline media, elevating [K] alleviated the growth reduction of RB at low salinity, and S at both low and high salinity. This ameliorative effect of K may be attributed to the suppression of both Na+ uptake, and Na + translocation in the plant.

Three distinct K$ sp+$ currents were identified in corn (Zea mays) protoplasts using the whole-cell patch-clamp technique. Inward-rectifying K$ sp+$ currents were evoked at membrane potentials more negative than $-$100 mV. The activation range was sensitive to external K$ sp+$ and shifted in the positive direction as the K$ sp+$ concentration was elevated. The second K$ sp+$ current was voltage-independent and contributed to the resting membrane conductance of the protoplast. Finally, a voltage- and Ca$ sp{2+}$-dependent K$ sp+$ current was observed at potentials positive to $-$60 mV. This current was inhibited by reagents which antagonize plasmalemma Ca$ sp{2+}$ influx (e.g. nitrendipine, verapamil). In contrast, currents were enhanced by increasing the cytosolic free Ca$ sp{2+}$ concentration from 40 to 400 nM. The Ca$ sp{2+}$-dependent K$ sp+$ current was inhibited by tetraethylammonium ions, Cs$ sp+$, Ba$ sp{2+}$, and charybdotoxin which suggested that the channel protein has structural similarities to the high conductance Ca$ sp{2+}$-dependent K$ sp+$ channel observed in animal systems.

Thermogravimetry, coupled with a mass spectrometer (TG-MS) was used to investigate the catalytic effect potassium carbonate (K2CO3) and potassium chloride (KCl), on the char conversion and the product gas composition of chars derived from a South African inertinite-rich bituminous coal. Sequential leaching of the coal with HCl-HF-HCl was performed to reduce the mineral matter present in the coal. This was done in order to reduce possible undesirable interactions between the minerals and inorganic compounds in the coal during heat treatments. The leaching process substantially reduced the ash content from 21.5% to less than 3%. K2CO3 and KCl [0.5, 1, 3, 5 K-wt %] were loaded to the demineralized coal, raw coal and demineralized coal with added mineral mixture prior to charring. The mineral mixture was made up of kaolinite, quartz, pyrite, siderite, calcite, anastase and hydromagnesite. The ‘doped’ coal samples were then subjected to heat treatments in a CO2 atmosphere up to 1200 °C. The results obtained showed that both K2CO3 and KCl exhibit a catalytic effect on the char conversion during heat treatments in CO2 atmosphere and the char conversion was increased with increasing loadings up to 5 K-wt% of K2CO3 and KCl. The temperature ranges at which conversion occurred were found to be lower for K2CO3 than for KCl. Subsequently, char conversion occurred over a relatively narrower temperature range for K2CO3 than observed for KCl. The catalytic behaviour of K2CO3 and KCl was confirmed by the results obtained. The results also indicated that the catalytic influence of K2CO3 is greater than that of KCl and that KCl is more susceptible to deactivation by minerals and inorganic compounds present in the coal than K2CO3. Different analytical techniques (XRF and XRD) were used to determine the extent of interaction of the catalysts used with the char material in the 5 K-wt% ‘doped’ coal samples. From the XRF results, it was observed that the K2O content was reduced after heat treatments in CO2, however, no potassium crystalline phases were observed in the XRD results after heat treatments in CO2. The reduced K2O content may be attributed to the potassium been taken up in other mineral matter during char reaction with CO2, forming new amorphous inorganic complex compounds. Thus the potassium retained in the sample after heat treatment, indicated by the XRF results, may be in an amorphous phase. Mass spectrometry (MS) indicated that temperatures at which the maximum rate of evolution of gaseous species occurred were relatively lower for K2CO3 loaded char samples iv than observed for KCl loaded samples. In addition, no mass-to-charge ratio (m/z) peak at 39 atomic mass unit (amu) from the MS results was observed, indicating that no potassium was detected in the gaseous phases for all the char samples. The undetected potassium in the gaseous phase may be due to the detection limit of the MS equipment. The MS results also indicated that addition of the catalyst facilitates the evolution of H2 from the coal char samples. Addition of the catalysts to the samples lowered the temperature at which maximum H2 was given off. The shift to lower temperatures was observed with increased catalyst loadings for both K2CO3 and KCl loaded samples. / Thesis (MSc (Chemistry))--North-West University, Potchefstroom Campus, 201

Thermogravimetry, coupled with a mass spectrometer (TG-MS) was used to investigate the catalytic effect potassium carbonate (K2CO3) and potassium chloride (KCl), on the char conversion and the product gas composition of chars derived from a South African inertinite-rich bituminous coal. Sequential leaching of the coal with HCl-HF-HCl was performed to reduce the mineral matter present in the coal. This was done in order to reduce possible undesirable interactions between the minerals and inorganic compounds in the coal during heat treatments. The leaching process substantially reduced the ash content from 21.5% to less than 3%. K2CO3 and KCl [0.5, 1, 3, 5 K-wt %] were loaded to the demineralized coal, raw coal and demineralized coal with added mineral mixture prior to charring. The mineral mixture was made up of kaolinite, quartz, pyrite, siderite, calcite, anastase and hydromagnesite. The ‘doped’ coal samples were then subjected to heat treatments in a CO2 atmosphere up to 1200 °C. The results obtained showed that both K2CO3 and KCl exhibit a catalytic effect on the char conversion during heat treatments in CO2 atmosphere and the char conversion was increased with increasing loadings up to 5 K-wt% of K2CO3 and KCl. The temperature ranges at which conversion occurred were found to be lower for K2CO3 than for KCl. Subsequently, char conversion occurred over a relatively narrower temperature range for K2CO3 than observed for KCl. The catalytic behaviour of K2CO3 and KCl was confirmed by the results obtained. The results also indicated that the catalytic influence of K2CO3 is greater than that of KCl and that KCl is more susceptible to deactivation by minerals and inorganic compounds present in the coal than K2CO3. Different analytical techniques (XRF and XRD) were used to determine the extent of interaction of the catalysts used with the char material in the 5 K-wt% ‘doped’ coal samples. From the XRF results, it was observed that the K2O content was reduced after heat treatments in CO2, however, no potassium crystalline phases were observed in the XRD results after heat treatments in CO2. The reduced K2O content may be attributed to the potassium been taken up in other mineral matter during char reaction with CO2, forming new amorphous inorganic complex compounds. Thus the potassium retained in the sample after heat treatment, indicated by the XRF results, may be in an amorphous phase. Mass spectrometry (MS) indicated that temperatures at which the maximum rate of evolution of gaseous species occurred were relatively lower for K2CO3 loaded char samples iv than observed for KCl loaded samples. In addition, no mass-to-charge ratio (m/z) peak at 39 atomic mass unit (amu) from the MS results was observed, indicating that no potassium was detected in the gaseous phases for all the char samples. The undetected potassium in the gaseous phase may be due to the detection limit of the MS equipment. The MS results also indicated that addition of the catalyst facilitates the evolution of H2 from the coal char samples. Addition of the catalysts to the samples lowered the temperature at which maximum H2 was given off. The shift to lower temperatures was observed with increased catalyst loadings for both K2CO3 and KCl loaded samples. / Thesis (MSc (Chemistry))--North-West University, Potchefstroom Campus, 201

Following the Chernobyl accident in 1986, a range of countermeasures has been developed to reduce the transfer of 137Cs from soil to plant and from the plant into grazing animals. One such countermeasure is the application of potassium to the soil. However, little is known of any side-effects such an application may have on the ecosystem, the longevity of the application and the effectiveness in a range of soil types. An application of potash (KCl) was made to four organic upland soils in Cumbria. England at two application rates of 100 and 200 kg K ha-1 in June 1997 and at a single site in June 1998. Following application. a range of parameters within the ecosystem were recorded, through the collection of monthly samples of sail, vegetation and water samples over a period of fifteen months. The results indicate that the application was effective for at least one year following application, that a lag phase existed between potash application and any effect within each ecosystem and that the duration of this phase was site specific. The results also showed that the countermeasure was effective at all sites and there was little apparent difference between the two application rates. The parameters measured which included soil pH, plant biomass, changes in Cu, K, Mg, Mn and Ca concentrations within the soil and vegetation indicated only a relatively small effect of the application on the ecosystem as a whole. The application can be considered as a viable option for reducing the transfer of 137Cs from soil to plant. The study also shows that the effectiveness of the application is dependent on the measurement used. i.e. concentration ratios, Tag values or a total flux approach. It is argued that the flux approach is the most appropriate basis for comparing the effectiveness of potash as a countermeasure between several sites.

Potassium is one of the essential plant nutrient elements. It is used by plants in the synthesis and distribution of carbohydrates and in the formation of proteins and oils. Potassium also seems to exert many of tis effects by influencing enzymatic activity in cells. The fact that potassium is being removed from Utah soils at a rather rapid rate raises the question as to whether any apprecialbe proportion of these soils are now deficient or are approaching a deficiency in this element. Some farmers, fertilizer salesmen, and others, have expressed a belief that many soils of the state are now at a deficiency level. Workers in the Utah Agricultural Experiment Station report that field experiments indicate no crop responses to potassium fertilizers and express that opnion that soil deficiencies in potassium are not common here. The purpose of this investigation is to evaluate present information regarding the need for potassium fertilizers in Utah soils and to study some of the soil types in regard to their contents of available potassium and probable need for potash fertilizers in the near future.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2007. / Härtill 5 uppsatser.