Nearest Neighbor Classification Rule for Mixtures of Discrete and Continuous Random Variables

In this paper very simple nonparametric classification rule for mixtures of discrete and continuous random variables is described. It is based on the method of nearest neighbor proposed by Cover and Hart (1967). The bounds on the limit of the nearest neighbor rule risks are given. Both lower and upper bound depend on the Bayes risk and the loss function. Finally the method is compared with other existing methods on some practical data set.     

Environmental factors influencing the vertical migration of planktonic rotifers in a hypereutrophic tarn

The diel vertical migration of planktonic rotifers in a small, hypereutrophic tarn was investigated on four occasions in 1983. When the tarn was isothermal the rotifers were distributed throughout the water column. After stratification, the rotifers were confined to the top 1–2 m of oxygenated water. On all four dates the rotifers were aggregated at specific depths in the water column. On some occasions, the pattern of aggregation changed as the animals performed distinct diurnal migrations. Keratella cochlearis, K. quadrata and Polyarthra vulgaris usually followed the reverse migrations of the phytoplankton. In contrast, the movements of Anuraeopsis fissa were less pronounced and were associated with variations in the depth of the oxycline.     

Cranial variation in European populations: a spatial autocorrelation study at three time periods

This study reports on spatial variation of 10 cranial variables in European populations at 3 time periods. Means for these variables, based on 137, 108, and 183 samples from the Early Medieval, Late Medieval, and Recent periods, were subjected to one-dimensional and directional spatial autocorrelation analyses. Significant spatial structure was found for most variables. It becomes more pronounced as time progresses. The spatial patterns are not strongly clinal. Correlograms based on distances computed from all variables are monotonic only to 900, 1,650, and 1,350 km for the three periods. Regional patterns are seen for most variables and become more structured and significant with time. There is little similarity among the correlograms of the variables at any one period and virtually none among periods. Inferences about spatial structure of these populations, based on spatial autocorrelation analysis, suggest a pattern dominated by migration, followed by expansion and admixture rather than selection or chance fluctuations. The patterns of morphometric change seem to reflect the patterns of linguistic change in these areas.     

Morphological traits and common illness in newborn infants

The present study focussed on neonates morbidity in connection with the morphological traits in the individual relative to the population average and in connection with the fluctuating asymmetry (FA) in 8 bilateral traits. The sample comprised two categories of newborn infants: 1) 1088 full term children, in which body weight (W), body height (H) and head circumference (HC) were measured on the day of birth; and 2) 216 infants of various gestation age (from 26 to 41 weeks) in which 6 measurements of upper and lower arm breadth, plus ear length and breadth on both sides of the body, were made during the first 72 hours of life. Relevant vital statistics were also obtained from parents. The following major categories of morbidity were observed in our samples: jaundice, respiratory diseases, cardiovascular diseases, urinary tract infections (only in the second sample), haematological diseases and ‘varia’. The results show that W, H, HC and W/H² index are significantly correlated with a predisposition to various categories of morbidity. For W and W/H² index, this correlation remains significant even after adjustment for diverse anthropometric and demographic variables. In the case of urinary tract infection, the contribution of HC also remains significant even after the adjustment procedure. Gestational age and cardiovascular illnesses yielded significant correlations with mean FA. There was an evident decrease in mean FA upon increase of gestational age. The mean FA of infants suffering from cardiovascular morbidity displays the same trend, although it is consistently higher compared to the total group of infants in the respective gestational age.     

Na+ and K+ fluxes stimulated by Na+-coupled glucose transport: Evidence for a Ba2+-insensitive K+ efflux pathway in rabbit proximal tubules

Summary Addition of glucose or the nonmetabolizable analogue -methyl-d-glucoside to rabbit proximal tubules suspended in a glucoseand alanine-free buffer caused a sustained increase in intracellular Na⁺ content (+43±7 nmol · (mg protein)^–1) and a concomitant but larger decrease in K⁺ content (–72±11 nmol· (mg protein)^–1). A component of the net K⁺ efflux was Ba²⁺ insensitive, and was inhibited by high (1mm) but not low (10 m) concentrations of the diuretics, furosemide and bumetanide. The increase in intracellular Na⁺ content is consistent with the view that the increased rates of Na⁺ and water transport seen in the proximal tubule in the presence of glucose can be attributed (at least in part) to a stimulation of basolateral pump activity by an increased [Na⁺] _i .     

Ca2+-activated K+ conductance causes membrane hyperpolarizations in a monkey kidney cell line (JTC-12)

Summary We have previously reported hyperpolarizing membrane potential changes in a monkey kidney cell line (JTC-12) which has characteristics resembling proximal tubular cells. These hyperpolarizations could be observed spontaneously or evoked by mechanically touching adjacent cells. In this report, we have shown further evidence that these hyperpolarizations are elicited by an increase in membrane conductance to K⁺ which is caused by an increase in cytosolic Ca²⁺ concentration. In addition, we have found another type of hyperpolarization which is evoked by applying flow of extracellular fluid to the cell. Intracellular injection of Ca²⁺ and Sr²⁺ evoked hyperpolarizations, while intracellular injection of Mn²⁺ and Ba²⁺ did not. Intracellular injection of EGTA suppressed both spontaneous and mechanically evoked hyperpolarizations. In Ca²⁺-free medium, both spontaneous and flow-evoked hyperpolarizations were not observed, while mechanical stimuli consistently evoked hyperpolarization. In Na⁺-free medium, the incidence of cells showing the spontaneous or flow-evoked hyperpolarization increased, and the amplitude and the duration of the mechanically evoked hyperpolarization became greater. Quinidine inhibited all types of hyperpolarization. These data suggest that hyperpolarizations in JTC-12 cells are due to an increase in Ca²⁺-activated K⁺ conductance.     

An in vitro test for measuring cytotoxicity of mercuric chloride to human kidney epithelial cells by specific enzyme release

Mercuric compound toxicity is well documented in animals and man for practically all organs. The recent development of cell culture techniques appeared as a novel fruitful tool in toxicology, especially in renal toxicology. Heavy metal induced renal cell alterations can be evaluated by membrane permeability damages.The present study evaluates mercuric chloride nephrotoxic effect in human kidney epithelial cells by measuring the release of two specific nephrotoxicity marker enzymes, Gamma Glutamyl Transferase (GGT) and Alkaline Phosphatase (ALP) in the culture medium. Cultured kidney epithelial cells were exposed to different HgCl₂ concentrations (5, 10, 20, and 50 g). Cultures were examined after 6 and 24 hours exposure. A good correlation between mercury dose and toxic effect, and exposure time and toxic effect was found. Enzymes were significantly released into the culture medium for 5 g and 10 g HgCl₂/ml after 6 hours exposure; and after 24 hours exposure, enzymes were released for 5 g/ml only.It appears that the specific tubular enzyme release in the culture medium is a good in vitro test for quantification of specific tubular damage.     

Initiation and characterization of primary mouse kidney epithelial cultures

Summary Primary cultures of murine renal epithelial cells were established from a preparation of proximal tubule fragments. Confluent cultures exhibited multiple dome formation, indicating the presence of tight junctions and an intact transcellular transport process. Ultrastructural analysis revealed a monolayer of polarized cells, with a sparse but clearly defined microvillar surface facing the growth medium and a basolateral surface attached to the substratum. Cultures grown on collagen gels did not show domes. The epithelial monolayer exhibited several differentiated functions of the proximal tubule: a) parathyroid hormone (PTH)-stimulated cAMP synthesis; b) production of 24,25-dihydroxyvitamin D₃ from 25-hydroxyvitamin D₃; c) high alkaline phosphatase activity; and d) Na⁺-dependent transport of phosphate (Pi) and α-methylglucoside (α-MG). The sugar uptake was selectively inhibited by phlorizin, a competitive inhibitor of glucose uptake at the luminal membrane. Kinetic analysis revealed independent transport systems for Pi and α-MG, with Km values corresponding to the high affinity systems identified in brush border membrane vesicles derived from the proximal tubule. Pi uptake by the epithelial monolayers was regulated by the concentration of Pi in the growth medium. Phorbol esters and PTH did not exert an effect on Pi and α-MG transport in mouse primary cultures. The present study demonstrates that primary cultures provide a useful in vitro preparation to investigate renal proximal tubular function. Cindy Bell was the recipient of an MRC Studentship Award. This work was supported by the MRC (Group in Medical Genetics). This is publication number 88011 of the McGill University-Montreal Children's Hospital Research Institute.