Effects of temperature and CO2 enrichment on kinetic properties of phospho-enol-pyruvate carboxylase in two ecotypes of Echinochloa crus-galli (L.) Beauv., a C4 weed grass species

Summary Two populations of Echinochloa crus-galli (Québec, Mississippi) were grown at the Duke University Phytotron under 2 thermoperiods (28°/22°C, 21°/15°C day/night) and 2 CO₂ regimes (350 and 675 l l^-1). Thermostability, energy of activation (E _a ),K _m (PEP), K _m (Mg⁺⁺), and specific activity of phospho-enol-pyruvate carboxylase (PEP_c) were analyzed in partially purified enzyme preparations of plants grown for 5 weeks. Thermostability of PEP_c from extracts (in vitro) and leaves (in situ) was significantly higher in Mississippi plants. In vitro denaturation was not appreciably modified by thermal acclimation but CO₂ enrichment elicited higher thermostability of PEP_c. In situ thermostability was significantly higher than that of in vitro assays and was higher in Mississippi plants acclimated at 28°/22°C and in plants of the two ecotypes grown at 675 l l^-1 CO₂. E _a (Q ₁₀ 30°/20°C) for PEP_c was significantly lower in Québec plants as compared to Mississippi and no acclimatory shifts were observed. Significantly higher K _m's (PEP) in 20°C assays were obtained for Mississippi as compared to Québec plants but values were similar at 30°C and 40°C assays. K _m (Mg⁺⁺) decreased at higher assay temperatures and were significantly lower for PEP_c of the Québec ecotype. No significant changes in K _m (Mg⁺⁺) values were associated with modifications in temperature on CO₂ regimes. PEP_c activity measured at 30°C was significantly higher for Québec plants when measured on a leaf fresh weight, leaf area or protein basis but not on a chlorophyll basis. Significantly higher PEP_c activity for both genotypes was observed for plants acclimated at 21°/15°C or grown at 675 l l^-1 CO₂. Net photosynthesis (Ps) and net assimilation rates (NAR) were higher in Québec plants and were enhanced by CO₂ enrichment. NAR was higher in plants acclimated at low temperature, while an opposite trend was observed for Ps. PEP_c activities were always in excess of the amounts required to support observed rates of CO₂ assimilation.     

Genetic markers in Malaysians: Variants of soluble and mitochondrial glutamic oxaloacetic transaminase and salivary and pancreatic amylase,phosphoglucomutase III and saliva esterase polymorphisms

Summary Malaysians of Malay, Chinese, and Indian ancestries were electrophoretically phenotyped for Amy₁ and saliva esterase region 1(Set-1) from saliva, Amy₂ from plasma, soluble and mitochondrial GOT and PGM ₃ from leukocyte and placenta. Kadazans and Bajaus, the indigenous people of Sabah, East Malaysia were surveyed for Amy₂. Three types of variants were observed for Amy₁, one type for Amy₂. Only Indians were found to be polymorphic for Amy₁. Two GOT _s 2-1 and three GOT _m 2-1 variants were found among 281 Chinese while three GOT _m 2-1 variants were found among 311 Malays.Malaysian Malays, Chinese, and Indians were found to be polymorphic for Set-1 and PGM ₃. The gene frequencies in Malays are Set-1F=0.601±0.021, Set-1S=0.399±0.021; PGM ₃ ¹ =0.788±0.020, PGM ₃ ² =0.212±0.020; in Chinese Set-1F=0.497±0.028, Set-1S=0.503±0.028; PGM ₃ ¹ =0.745±0.024, PGM ₃ ² =0.255±0.024; in Indians, Set-1F=0.449±0.031, Set-1S=0.551±0.031; PGM ₃ ¹ =0.755±0.029, PGM ₃ ² =0.245±0.029.     

Isoelectric focusing of human red cell phosphoglucomutase (PGM1). Phenotype distribution in the population of Tuscany and two hereditary variants

Summary Phosphoglucomutase (PGM₁) phenotypes were determined in a population sample of Tuscany, Italy, by isoelectric focusing. The frequencies observed for the four alleles are: PGM ₁ ¹⁺ =0.6012, PGM ₁ ^1- =0.1059, PGM ₁ ²⁺ =0.2495, PGM ₁ ^2- =0.0434. Two variants were detected and it was possible to study the parentage of both of them. The pedigree of the propositus of the first variant shows that the variant occurs in combination with the common alleles PGM₁ 1+ and PGM₁ 2+ and that it has an autosomal dominant inheritance. The second variant has been shown to be a product of the PGM₂ locus, although its PAGIF pattern is included between 2- and 1+ isoenzymes.     

Metabolic and hormonal responses during exercise at 20°, 0° and −20°C

This study was designed to clarify the effects of cold air exposure on metabolic and hormonal responses during progressive incremental exercise. Eight healthy males volunteered for the study. Informed consent was obtained from every participant. The following protocol was administered to each subject on three occasions in a climatic chamber in which the temperature was 20°, 0° or –20°C with relative humidity at 60%±1%. Exercise tests were conducted on an electrically braked ergocycle, and consisted of a propressive incremental maximal exercise. Respiratory parameters were continuously monitored by an automated open-circuit sampling system Exercise blood lactate (LA), free fatty acids (FFA), glucose levels, bicarbonate concentration (HCO ₃ ^– ), acidbase balance, plasma epinephrine (E) and norepinephrine (NE) were determined from venous blood samples obtained through an indwelling brachial catheter. Maximal oxygen uptake was significantly different between conditions: 72.0±5.4 ml kg^–1 min^–1 at 20°C; 68.9±5.1 ml kg^–1 min^–1 at 0°C and 68.5±4.6 ml kg^–1 min^–1 at –20°C. Workload, time to exhaustion, glucose levels and rectal Catecholamines and lactate values were not significantly altered by thermal conditions after maximal exercise but the catecholamines were decreased during rest. Bicarbonate, respiratory quotient, lactate and ventilatory thresholds increased significantly at –20°C. The data support the contention that metabolic and hormonal responses following progressive incremental exercise are altered by cold exposure and they indicate a marked decrease in maximal oxygen uptake, time to exhaustion and workload.This study was supported by grants from CSR, Univesité du Québec; FIR, Université du Québec à Trois-Rivières and NATO no, 86.0435.     

Using satellite imagery to assess breeding habitat availability of the endangered loggerhead shrike in Québec

The loggerhead shrike (Lanius ludovicianus) is a grassland bird species whose preferred nesting habitat in eastern Canada is pastureland. This species has been extirpated from much of its historical range in this region, and breeding habitat loss is suspected to be an important cause of this decline. We evaluated the availability of suitable breeding habitats in Québec using satellite imagery. Because this species no longer breeds in Québec, we established habitat selection criteria from known nesting sites in the adjacent province of Ontario, from analysis of a Landsat-TM satellite image, and applied these criteria to Landsat-TM images covering southern Québec. We developed regional landscape criteria in 100 km² plots and patch indices criteria at the pasture level. Spatial analyses were conducted to characterize plots and pastures on the basis of pasture availability and spatial distribution. Pastures suitable for nesting loggerhead shrikes were those fulfilling patch criteria at the pasture level and located in plots fulfilling regional landscape criteria. Overall, 310 out of 1700 plots located in the historical breeding range of the loggerhead shrike in Québec fulfilled landscape criteria, supporting 3988 pastures that fulfilled patch criteria. More than 500 of these pastures were visited to validate their current status. The Outaouais region would be the most suitable region for nesting loggerhead shrikes in southern Québec, where suitable breeding habitat still remains because more than two-thirds of visited sites were still pastureland, hawthorns were well-distributed in the region, and pastureland fragmentation was lowest. We conclude that the availability of breeding habitat does not limit the establishment of a breeding population of loggerhead shrike in southern Québec, as we estimated that thousands of hectares of suitable habitat still remain in that province.     

Rare phenotypes of the phosphoglucomutase locus 1 detectable by isoelectric focusing on Cellogel

Summary The rare phenotypes PGM₁, determined by alleles PGM ₃ ¹ , PGM ₄ ¹ , PGM ₆ ¹ , and PGM ₇ ¹ were examined by starch gel electrophoresis and cellulose acetate gel isoelectric focusing and were compared with the commonest phenotypes of PGM₁.The frequencies of the rare genes found in the Polish populations were as follows: in Lublin, PGM ₃ ¹ =0.0002, PGM ₄ ¹ =0.0005, PGM ₆ ¹ =0.0010, and PGM ₇ ¹ =0.0005; in Wroclaw, PGM ₃ ¹ =0.0000, PGM ₄ ¹ =0.0005, PGM ₆ ¹ =0.0007, and PGM ₇ ¹ =0.0002.The results suggest that the F and S type variants of the genes PGM ₄ ¹ and PGM ₇ ¹ probably do not occur. It is still possibile that F and S variants exist for the genes PGM ₃ ¹ and PGM ₆ ¹ .     

Investigation of PGM13, PGM16, and PGM17 variants by isoelectric focussing. Evidence for new subtypes of the PGM 1 3 and PGM 1 7 alleles

Summary A total of 345 haemolysates previously phenotyped by starch gel electrophoresis and known to contain the products of the PGM ₁ ³ , PGM ₁ ⁶ , and PGM ₁ ⁷ alleles have been analyzed by thin layer polyacrylamide gel isoelectric focussing in the pH range 5–7. Two common subtypes, 3+and 3-, of the PGM ₁ ³ allele have been found in a number of Pacific populations. A single form of the PGM ₁ ⁷ allele was observed in the Western Caroline Islands. In contrast, one of two Indian PGM₁7 variants focussed to a different position when compared with the form found at polymorphic frequency in the Western Caroline Islands. Only one type of the PGM ₁ ⁶ allele was detected during the present investigation.     

Mercuric(II) chloride modulates single-channel properties of carbachol-activated Cl− channels in cultured neurons ofAplysia californica

Summary 1. The effect of mercuric(II) chloride on kinetic parameters of carbacholactivated single chloride channels were studied in cultured neurons of the marinemollusk, Aplysia californica.2. Single neurons ofAplysia were cultured in L-15 medium containing 1 mM -d-xyloside, which improved the success rate for gigaseal formation by 46%. Carbachol-activated single chloride channels were recorded in the cell-attached patch clamp configuration. Recordings with control solution (1 µM carbachol) and with test solution (1 µM carbachol +1 µM HgCl₂) were performed successively on the same neuron.3. In both the control and the test solution the open and closed time distributions were fitted with a double-exponential function. However, kinetic analysis revealed that Hg²⁺ caused a significant reduction of the mean closed time (10.37±1.08 vs. 3.32±0.02 msec) and of the second time constant ₂ of the closed time distribution (2.09±0.05 vs. 0.66±0.5 msec). The reduction of ₂, i.e., fewer events in the longer closed state under the action of Hg²⁺, may be the physical cause for the reduction of the mean closed time and thus underlies the increased open probabilityp ₀ (0.13±0.01 vs. 0.29±0.01 msec) of carbachol-activated chloride channels.4. Inorganic Hg²⁺ affects the acetylcholine receptor at lower concentrations than previously reported.     

Comparative study of DNA adducts levels in white sucker fish (Catostomus commersoni) from the basin of the St. Lawrence River (Canada)

The levels of DNA adducts in the hepatic tissue of the white sucker fish speciesCatostomus commersoni were determined by³²P-postlabelling. The fish were caught at four sites: two sites near the city of Windsor (Québec, Canada) on the St. François River, a downstream tributary of the St. Lawrence River, and two sites in the St. Lawrence River itself, near the city of Montréal (Québec, Canada). The latter sites are known to be contaminated by many pollutants including polycyclic aromatic hydrocarbons. Total adduct levels in all fish ranged from 25.1–178.0 adducts per 10⁹ nucleotides. White sucker from the selected sites of the St. Lawrence River had a significantly higher mean level of DNA adducts than those of the St. François River (129.4 vs 56.8, respectively). These results suggest that the effluents of many heavy industries (e.g. from a Soderberg aluminium plant) flowing in the St. Lawrence River are more likely to produce genotoxic damage to fish than those released in one of its tributary, and mainly associated to the activities of a small town and a nearby pulp and paper mill.     

Short-term studies of 15NO3 - and 15NH4 + uptake by micropropagated strawberry shoots cultured with or without CO2 enrichment

The uptake of ¹⁵NO₃ ^- and ¹⁵NH₄ ⁺ has been examined in 5-,10- and 28-day-old micropropagated strawberry (Fragaria x ananassa Duch. cv. Kent) shoots rooted in one-half strength Murashige and Skoog (MS) liquid medium on cellulose plugs (Sorbarods). The results indicated that the plantlets absorbed both NO₃ ^- and NH₄ ⁺ during the culture with a greater uptake of NH₄ ⁺ at 5 days of culture. Furthermore, a pronounced reduction in NO₃ ^- and NH₄ ⁺ uptake at 10 and 28 days of culture was observed within 6 h of the short-term uptake study. This reduction could be explained by the low CO₂ concentration in test tubes during the photoperiod, since no reduction in nitrogen uptake occurred in the CO₂ enriched condition. The results are interpreted as an indication of the important role for photosynthetic CO₂ fixation in the process of nitrogen uptake by the plantlets during the rooting stage.Contribution No. CRH 82, Centre de Recherche en Horticulture, F.S.A.A., Université Laval, Québec.     

Isoelectric focusing of human red cell phosphoglucomutase

Summary A total of 637 individuals from the rural village of Keneba in The Gambia, West Africa, have been typed for red cell PGM using isoelectric focusing (pH 5–7) in polyacrylamide gels. Eight different phenotypes have been detected. The frequency of the four alleles at the PGM₁ locus was found to be PGM ₁ ¹⁺ 0.795, PGM ₁ ^1- 0.053, PGM ₁ ²⁺ 0.133, and PGM ₁ ^2- 0.019. A study of the PGM phenotypes in 89 families confirmed the simple Mendelian codominant inheritance of the four alleles. Comparative population data suggest that red cell PGM typing by isoelectric focusing might prove to be a useful genetic marker in anthropological studies.     

Secretion of electrolytes,protein and urea by the mandibular gland of the common wombat (Vombatus ursinus)

Saliva was collected from the mandibular glands of anaesthetized common wombats (Vombatus ursinus) to ascertain maximal flow rates, salivary compostion and possible adaptations, particularly PO₄ ^3- secretion, to assist digestion. After temporary catheterization of the main duct through its oral opening, salivary secretion was evoked at flow rates ranging from 0.02±0.002 (±SEM) ml·min^-1 (0.7±0.07 l·min^-1·kg body weight^-1) to 0.4±0.05 ml·min^-1(14±1.9 l·min^-1·kg body weight^-1) by ipsilateral intracarotid infusion of acetylcholine. The [Na⁺] (15±5.1 to 58±8.6 mmol·l^-1) and [HCO₃ ^-] (35±1.9 to 60±1.9 mmol·l^-1) were positively correlated with salivary flow rate. The [K⁺] (58±5.2 to 30±2.4 mmol·l^-1), [Ca²⁺] (10.4±1.67 to 4.1±0.44 mmol·l^-1), [Mg²⁺] (0.94±0.137 to 0.17±0.032 mmol·l^-1), [Cl^-] (71±9.2 to 45±6.0 mmol·l^-1), [urea] (9.3±0.79 to 5.1±0.54 mmol·l^-1), H⁺ activity (29±1.6 to 17±1.6 nEq·l^-1) and amylase activity (251±57.4 to 92±23.3 kat·l^-1) were negatively correlated with flow. Both concentration and osmolality fell with increasing flow at the lower end of the flow range but osmolality always increased again by maximal flow whereas the relation between protein and flow was not consistent at the higher levels of flow and stimulation. Salivary [PO₄ ³⁺] was not correlated with flow and at 3–14% of the plasma concentration was extremely low. Thus, in contrast to its nearest relative, the koala (Phascolarctos cinereus), the wombat secretes little PO₄ ³⁺ presumably because it does not need high levels of PO₄ ³⁺ in its saliva to facilitate microbial digestion of plant fibre.Abbreviations bw body weight - ww wet weight     

The production ofBacillus sphaericus 2362 using fermented cowpea (Vigna unguiculata) medium containing mineral substitutes from Nigeria

Summary A medium derived from local materials has been developed for the growth ofBacillus sphaericus Neide strain 2362, a potent larvicide of many mosquito species. The bacillus was grown on three concentrations (50, 100 and 150 g l^–1) of fermented whole bean (Vigna unguiculata) steep liquor and reached 2.8, 4.8 and 4.0×10⁹ c.f.u. ml^–1 respectively after 64 h. The concentration for killing 50% of the test larvae (Culex pipiens quinquefasciatus Say) were 16±0.09, 11±0.01 and 14±0.04 p.p.m. respectively. The LD₅₀ value of basal medium was 13±0.213 p.p.m.. Scale-up fermentation of the bacillus used 100 g cowpea steep liquor per litre of basal medium. For control of media pH, the juice ofCitrus aurantifolia and an extract fromElaeis guiniensis were used as sources of acid and alkali respectively.

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Resumen Apartir de materias primas locales se ha desarrollado un medio de cultivo paraBacillus sphaericus Neide cepa 2362, que es un potente larvicida contra muchas especies de mosquitos. El bacilo se hizo crecer a concentraciones de 50, 100 y 150 gl^–1 de extracto de caupí fermentado alcanzando después de 64 h, 2.8; 4.8 y 4.0×10⁹ unidades formadoras de colonias por ml respectivamente. Las concentraciones de estos cultivos necesarias para eliminar el 50% de las larvas tipo empleadas en el ensayo^* fueron de 16±0.09; 11±0.01 y 14±0.04 ppm respectivamente. La DL₅₀ del medio base fue de 13±0.213 ppm. Para le fermentación a escala semi-industrial del bacilo se utilizó 100 g de extracto de caupí por litro de medio base. Para controlar el pH del medio se utilizó el zumo deCitrus aurantifolia y un extracto deElaeis guiniensis como fuentes de ácido y álcali respectivamente.

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Résumé On a développé un milieu à base de matières locales pour la croissance duBacillus sphaericus Neide, souche 2362, un larvicide puissant pour plusieurs espèce de moustiques. On a fait croître leBacillus à trois concentrations (50, 100 et 150 g l^–1) de jus de trempage de pois entiers fermentés deVigna unguiculata. On a obtenu respectivement 2.8, 4.8 et 4.0×10⁹ cfu ml^–1 après 64 h. Les concentrations léthales à 50% pour les larves tests (Culex pipiens quinquefasciatus Say) étaient de 16±0.09, 11±0.1, et de 14±0.04 ppm respectivement. La valeur LD₅₀ pour le milieu de base était de 13±0.213 ppm. La transposition à plus grande échelle de la production duBacillus s'est faite en utilisant 100 g de jus de trempage de la vigna par litre de milieu de base. Le contrôle du pH du milieu a été effectué par le jus deCitrus aurantifolia et un extrait deElaeis guiniensis comme source d'acide et de base respectivement.

     

Biogeography of copepods in lakes and ponds of subarctic Québec,Canada

We aimed to determine whether the copepod assemblages in lakes and ponds of northern Québec, Canada, were closer in composition to those found in southern Québec, or to those reported from the subarctic and arctic. Six calanoid and five cyclopoid species were identified from 37 ponds and lakes located in the region between 55° N and 59° N. Species diversity was generally low, ranging from 0 to 4 species per lake. Dominant species were Leptodiaptomus minutus and Acanthocyclops vernalis. The species assemblages showed high affinity with those found in forested regions of southern Québec. Exceptions were Leptodiaptomus tyrrelli, previously only recorded west of Hudson Bay, and Hesperodiaptomus arcticus, hitherto recorded north of 58° N. Relationships between the lakes, species, and environmental variables were explored using multivariate analysis. Lakes situated along the coast and on two offshore islands clustered together and were characterised by higher conductivity and pH than those lakes located further inland. Leptodiaptomus tyrrelli was common in these coastal lakes. Canonical correspondence analysis revealed statistically significant relationships between copepod distributions and conductivity, dissolved organic carbon and pH. These three variables accounted for 70% of the variation in the species' distribution.     

Effects of various metabolites on two phosphoglucomutase allozyme activities from Drosophila melanogaster

The effects of various metabolites on the two most common phosphoglucomutase allozymes (PGM^A and PGM^B) in Drosophila melanogaster have been investigated in vitro. 2,3-Diphosphoglycerate (2,3DPG) inhibited PGM^A and PGM^B to the same degree in the presence of 25 µM glucose-1,6-diphosphate (G1, 6P₂). However a higher concentration of G1,6P₂ partially reversed the inhibition of PGM^A exerted by 2,3DPG, so that in the presence of 150 µM G1,6P₂ the inhibition of PGM^A was half that of PGM^B at pH 6.0. Glycerol-3-phosphate (G3P) had no significant effect at pH 7.4 but exerted an activating effect at pH 6.0 which was more pronounced in the case of PGM^B. ATP, citrate, and fructose-1, 6-diphosphate (F1,6P₂) inhibited both PGM^A and PGM^B. The differences found in vitro between these two allozymes can have a significant impact on in vivo function and, therefore, on the maintenance of PGM polymorphism in experimental populations of D. melanogaster studied in the laboratory.     

Area prioritization for biodiversity conservation in Québec on the basis of species distributions: a preliminary analysis

Results are presented which prioritize areas for potential protection in Québec on the basis of biodiversity considerations. These results are relevant to the ongoing public discussion in Québec about designating new parks and refuges so that the province may fulfil its obligations to Canada's Endangered Spaces Campaign. The prioritization algorithm used in this analysis is based on rarity and complementarity. It attempts to sample biodiversity in as area-efficient a way as possible. The biodiversity surrogates used here comprise a subset of 743 species for which data on spatial distributions are publicly available; the analysis begins with 394 species at risk. It is shown that: (i) the existing network of protected areas in Québec does a poor job of protecting these biodiversity surrogates; (ii) adding adjacent areas to this network will not be the optimal way of protecting these biodiversity surrogates; (iii) many of the areas that have highest priority are in southern Québec, which has a high human population density; (iv) because of (iii), designating parks may not be economically or sociologically feasible and more adaptive alternative conservation plans will have to be devised; (v) coastal areas, riparian habitats, and other wetlands should have high priority for protection but are currently very inadequately represented in the reserve network; (vi) there is some reason for concern about the clear-cut logging of boreal forests in northern Québec; and (vii) the islands, Île d'Anticosti and the Îles-de-la-Madeleine, emerge as being of very significant conservation value and plans for the protection of areas on them should be an immediate goal for biodiversity conservation in Québec.     

Ca<Superscript>2+</Superscript>-activated nonselective cation channels in rat neonatal atrial myocytes

A nonselective cation channel activated by intracellular Ca²⁺ was identified in inside-out membrane patches taken from cultured rat atrial myocytes. Ca²⁺ (0.01–1.00 mM) reversibly activated the channel in a concentration-dependent manner. The channel often showed a quick and irreversible rundown within a few minutes after patch excision. The I-V relationship of the channel was linear between –100 and +100 mV. The single channel conductance was 26.0 ± 0.5 pS and its open probability was weakly voltage-dependent. Ion-substitution experiments showed that the channel was permeable to monovalent cations (P_x/P_Cs: Li⁺ (1.5) = K⁺ (1.5)> Na⁺ (1.2) > Rb⁺ (1.1) > Cs⁺ (1.0)) but not to Cl^– (P_Cl/P_Cs < 0.01) and Ca²⁺ (P_Ca/P_Cs =0.02 ± 0.01). Present address: A.B. Zhainazarov UF Center for Smell and Taste, McKnight Brain Institute, University of Florida, 100 S Newell Dr., L1-131, P.O. Box 100015, Gainesville, FL 32610-0015, USA     

Effects of Temperature and CO(2) Enrichment on Carbon Translocation of Plants of the C(4) Grass Species Echinochloa crus-galli (L.) Beauv. from Cool and Warm Environments

Plants of Echinochloa crus-galli from Québec and Mississippi were grown under two thermoperiods (28°C/22°C, 21°C/15°C) and two atmospheric CO₂ concentrations (350 and 675 microliters per liter) to examine possible differential responses of northern and southern populations of this C₄ grass species. Translocation was monitored using radioactive tracing with short-lived ¹¹C. CO₂ enrichment induced a decrease in the size of the export pool in plants of both populations. Other parameters did not strongly respond to elevated CO₂. Low temperature reduced translocation drastically for plants from Mississippi in normal CO₂ concentration, but this reduction was ameliorated at high CO₂. Overall, plants from Québec had a higher ¹¹C activity in leaf phloem and a higher percentage of ¹¹C exported, whereas these northern plants had lower turnover time and smaller pool size than plants from the southern population.     

The rate of nutrient release from grass and dung following immersion in lake water

Summary Two experiments were carried out to determine the rate of release of ions to lake water from dry grass (largely Eragrostis species) and dung from elephant, impala and buffalo. The ions released most rapidly were PO₃ ^3- and K⁺, followed by NO₃ ^- and Ca²⁺ + Mg²⁺; the smallest increase was shown by Na⁺. In general, dung derived from grass released ions more rapidly than grass itself; the results are discussed in relation to ash analyses of grass and dung. The possible importance to Lake Kariba of the nutrients released by grass and dung following immersion under natural conditions is considered.

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Résumé On a procédé à la réalisation de deux expériences visant à déterminer la vitesse de libération des ions dans l'eau d'un lac à partir d'herbe sèche (appartenant principalement à l'espèce Eragrostis) et de crottin d'éléphant, d'impala et de buflle. Par ordre décroissant, on mesure les vitesses de libération des ions les plus grands pour PO₄ ^3- et K⁺, et ensuite pour NO₃ ^- et Ca²⁺ + Mg²⁺; Na⁺ manifeste l'augmentation de concentration la plus faible. En règle générale, le crottin formé à partir d'herbe a libéré les ions à vitesse plus grande que l'herbe elle-même; les résultats sont interprétés par rapport à des analyses de cendre d'herbe et de crottin. On a cherché à estimer l'importance que peuvent présenter, pour le lac Kariba, la libération de ces éléments nutritifs après immersion dans des conditions naturelles.

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Present address: Biology Department, Chancellor College, University of Malawi, Limbe, MalawiN     

Non-Markovian Gating of Ca2+-Activated K+ Channels in Cultured Kidney Cells Vero. Rescaled Range Analysis

Using the patch-voltage clamp technique and the rescaled range method, activity of single large conductance Ca²⁺-activated K⁺ channels (K_Ca channels) was studied. For the sequences of alternating open and shut time intervals, the dependence R/S vs. N in the double logarithmic coordinates presented a curve with two slopes, H₁ =0.60 ± 0.04, and H₂ = 0.88 ± 0.21, where H₁ and H₂ characterized the Hurst exponents for shot and long time ranges, respectively. Similar results were obtained for reduced data sets consisting of only open or only shut intervals. Randomization of the experimental data resulted in a single slope, H, of 0.52 ± 0.02. Simulations were performed with eight-state Markovian model without memory. The calculated Hurst exponent presented in average 0.54 ± 0.02. The results suggest that the activity of single Ca²⁺-activated K⁺ channel exhibits two regimes, with slight positive correlation at short time ranges (H₁ =0.6), and strong positive correlation at long time ranges (H₂ = 0.88); therefore the channel gating as a whole is not a steady-state Markovian process.