Factors responsible for the differences in cultural estimates and direct microscopical counts of populations of bacterivorous nanoflagellates

Bacterivorous nanoflagellates (microflagellates) have been routinely enumerated in marine and freshwater samples using either a Most Probable Number (MPN) culture method or by a direct microscopical counting method (DC). These two techniques typically yield highly disparate estimates of the density of nanoflagellates in natural samples. We compared these methods with seawater and marine snow (macroscopic detrital aggregate) samples collected from surface waters throughout the North Atlantic and in freshwater samples collected at three stations in Lake Ontario. Densities of nanoflagellates determined by the two methods differed by as much as four orders of magnitude; the MPN estimate rarely exceeded 10% of the microscopical count, and averaged 1% of this count. The MPN estimate constituted a higher percentage of the DC value in environments with high concentrations of nanoflagellates relative to environments with low concentrations of nanoflagellates. The ratio of the culture count to the microscopical count (MPNDC) increased along an environmental gradient from oligotrophy to eutrophy, and was positively correlated with the density of bacteria in the samples. In laboratory experiments with two species of bacterivorous nanoflagellates, the MPN count constituted a much greater percentage of the DC count during the exponential growth phase of the nanoflagellate than during the stationary growth phase. Differences in the estimates of nanoflagellate density obtained with these two techniques probably can be explained by the trophic mode of these protozoa, their growth stage, and the amenability of these species to laboratory culture.     

The influence of experimental conditions on the spectrin-hemoglobin interaction

Human spectrin, when isolated, purified and stored in such conditions that preserve its tetrameric form, is able to associate with human hemoglobin as it is clearly shown by gel filtration. However, this hemoglobin-spectrin association does not seem to have a significant effect on hemoglobin oxygenation as indicated by equilibrium and rapid kinetics measurements.     

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The occurrence and distribution of certain polypeptides within the human carotid body

Summary Both carotid bodies from 26 patients coming to necropsy were fixed in 10% neutral buffered formalin and sections 4 m thick were stained for various peptides by use of the immunogold technique. The results show that the human carotid body contains met- and leu-enkephalin, substance P, vasoactive intestinal peptide (VIP), neurotensin and bombesin. The distribution of these six peptides within the carotid body differs. Thus met- and leu-enkephalin are both present predominantly within glomic chief cells but with a marked tendency to favour the dark variant of these cells. Substance P and VIP both show a weak immunoreactivity in comparison to the enkephalins and are present in all three variants of chief cell. Neurotensin shows the weakest immunoreactivity of all and is restricted to a few glomic chief cells in a minority of cases. Bombesin also shows a weak immunoreactivity in glomic chief cells but a strong reaction in glomic arteries and arterioles. In these vessels bombesin appears to be confined to smooth muscle cells in the media but we cannot say whether it is secreted by them or merely bound to receptor sites on their membranes. These findings are related to quantitative data on the concentration of peptides in the human carotid body from a previous paper with which we were associated.     

Evolutionary conservation of the human homologue of the yeast cell cycle control gene cdc2 and assignment of Cd2 to chromosome 10

Summary The human homologue of the fission yeast Schizosaccharomyces pombe cell cycle control gene cdc2 has been assigned to chromosome 10. DNA hybridization reveals that this gene is highly conserved in vertebrates. The human CDC2 gene probe detects a simple two-allele polymorphism in Taq1-digested DNA.     

Osmotic effectors in kidneys of xeric and mesic rodents: corticomedullary distributions and changes with water availability

Summary Urea, sodium, the methylamines glycine betaine and glycerophosphorylcholine (GPC), and the polyols sorbitol and myo-inositol are reported to be the major osmolytes in kidneys of laboratory mammals. These were measured (millimoles per kilogram wet weight) in kidney regions and urines of three species of wild rodents with different dehydration tolerances: the pocket mousePerognathus parvus (xeric), voleMicrotus montanus (mesic), and deer mousePeromyscus m. gambeli (intermediate). In animals kept without water for 4–6 days, sodium, urea, betaine and GPC+choline were found in gradients increasing from cortex to outer to inner medulla in all species, withPerognathus having the highest levels. Sorbitol was high in the inner medulla but low in the cortex and outer medulla; inositol was highest in the outer medulla. Totals of methylamines and methylamines plus polyols in the medulla showed high linear correlations (positive) with urea and with sodium values.Whole medullae were analyzed at several time points inMicrotus andPeromyscus subject to water diuresis followed by antidiuresis. In 102 h diuresis inMicrotus, all osmolytes decreased except inositol; however, only urea, sodium and sorbitol reached new steady states within 24 h. Urea returned to initial values in 18 h antidiuresis, while other osmolytes required up to 90 h. InPeromyscus, all osmolytes except the polyols declined in diuresis (max. 78 h test period). During antidiuresis, urea and GPC+choline rose to initial values in 18 h, with sodium and betaine requiring more time. In plots of both species combined, total methylamines+polyols correlated linearly (positive) with sodium, and GPC+choline with urea.Estimates of tissue concentrations suggest that total methylamines+polyols can account for intracellular osmotic balance in all species in antidiuresis and that sufficient concentrations of methylamines may be present to counteract perturbing effects of urea on proteins.Abbrevations GPC Glycero-3-phosphorylcholine - TCA trichloroacetic acid - M+P methylamines plus polyols     

pH Dependence of Histidine Affinity for Blood-Brain Barrier Carrier Transport Systems for Neutral and Cationic Amino Acids

The effects of pH (3.5-7.5) on the brain uptake of histidine by the blood-brain barrier (BBB) carriers for neutral and cationic amino acids were tested, in competition with unlabeled histidine, arginine, or phenylalanine, with the single-pass carotid injection technique. Cationic amino acid ( [14C]arginine) uptake was increasingly inhibited by unlabeled histidine as the pH of the injection solution decreased. In contrast, the inhibitory effect of unlabeled histidine on neutral amino acid ( [14C]phenylalanine) uptake decreased with decreasing pH. Brain uptake indices with varying histidine concentrations indicated that the neutral form of histidine inhibited phenylalanine uptake whereas the cationic form competed with arginine uptake. Since phenylalanine decreased [14C]histidine uptake at all pH values whereas arginine did not, it was concluded that the cationic form of histidine had an affinity for the cationic carrier, but was not transported by it. We propose that the saturable entry of histidine into brain is, under normal physiological circumstances, mediated solely by the carrier for neutral amino acids.     

The X-ray induced G2 arrest in mouse eggs: a maternal effect involving a lack of polypeptide phosphorylation

Summary In some strains of mice, eggs when X irradiated during the pronuclear stage, undergo a mitotic block in the G₂ phase of the first cell cycle and cleave when the second division takes place in controls. The importance of this effect varies considerably with the strain and depends exclusively on the maternal genotype. In previous work, two-dimensional electrophoresis showed that eggs blocked at the one-cell stage after irradiation, undergo the same modifications in polypeptide synthesis as two-cell controls of the same age, except at the time of normal first mitosis, where three polypeptide sets of 30, 35 and 45 kDa appear only in cleaving controls. In the present study, we have found phosphorylations in dividing controls, on polypeptides of 30, 35 and 45 kDa. These phosphorylations are not seen in blocked irradiated eggs.     

The theory of the frequency response of ellipsoidal biological cells in rotating electrical fields

In this paper we have presented in as compact a form as possible the theoretical formalism that is needed to predict the frequency response of a biological cell of arbitrary ellipsoidal shape to a frequency dependant rotating external field. The formalism is much more complicated than that for a spherical or cylindrical cell where the radial vector is always parallel to the surface normal at each point of the surface. In addition to providing the theory we have demonstrated that the spin rate and its frequency dependance is very intimately related to the electrical properties of the cell interior and to that of the suspending fluid. It is possible to probe these properties of the cell and its environment by utilizing this technique. This aspect has been demonstrated by examining rotational changes as a function of the conductivity of both the cell interior and its suspending liquid. We also have shown, by considering a very simple model for the cell and the two dielectric constants, that the frequency spectrum is shape dependant. All our calculations have been carried out for "lossy" systems with frictional dissipation where energy minimization methods are no longer applicable. The invariant form of the Poynting vector forms the basis of the method.