Adaptation to salinity at the plant cell level

Summary Various mechanisms of adaptation of plant cells to salinity are reviewed: (1) protection of enzymes and maintenance of turgor by organic solutes; (2) prevention of ion toxicity by compartmentation; and (3) energization of solute transport by the proton pump. All these mechanisms seem to play a role in adaptation. The particular advantages of using salt-adapted cells in suspension culture to identify mechanisms of adaptation are pointed out.     

On Comparing Correlated Means in the Presence of Incomplete Data

Two statistics are proposed for testing the hypothesis of equality of the means of a bivariate normal distribution with unknown common variance and correlation coefficient when observations are missing on both variates. One of the statistics reduces to the one proposed by Bhoj (1978, 1984) when the unpaired observations on the variates are equal. The distributions of the statistics are approximated by well known distributions under the null hypothesis. The empirical powers of the tests are computed and compared with those of some known statistics. The comparison supports the use of one of the statistics proposed in this paper.     

Development of membrane-potential responsiveness by myeloid leukemia cells during neutrophilic differentiation

The ability of a myeloid leukemia cell line (HL-60) to undergo membrane electrical potential changes was followed during neutrophilic differentiation induced by 2 compounds. Membrane-potential changes were induced with 12-O-tetradecanoylphorbol 13-acetate (TPA) or formyl-methionyl-leucyl-phenylalanine (FMLP) and were monitored by flow cytometry. The magnitude of the membrane-potential response to TPA increased in a more uniform manner as the population of cells matured than did acquisition of mature morphology or ability to undergo the respiratory burst in response to TPA. The response to TPA and FMLP of HL-60 cells, maximally induced to differentiate by dimethylsulfoxide, closely resembled that of neutrophils. Thus, HL-60 cells may be a useful tool in the study of the relation between membrane depolarization and subsequent cellular activation.     

The insertion of mesenchyme cells into the ectoderm during differentiation in Sea urchin embryos

Summary During the course of sea urchin development, from early blastula to pluteus larva, there are two major visible processes toward which all activities seem to be focused. They are the differentiation of the larval skeleton by the primary mesenchyme cells and the differentiation of the primitive gut by the secondary mesenchyme cells. These activities take place within the shell-like layer of epithelial cells, or ectodermal wall. The interactive role of the ectodermal wall with the mesenchyme cells is not yet clearly understood. A number of earlier studies have proposed that the ectoderm may have an inductive influence on the mesenchyme cells and that its inner surface forms a molecular template for guiding the mesenchyme cells. In this report, we suggest an additional role for the ectodermal wall. We show that some primary mesenchyme cells and secondary mesenchyme cells insert between the cells of the ectodermal wall in order to firmly anchor the anlage of the larval skeleton and primitive gut during differentiation. This mechanism may provide a physical basis for maintaining the stable positional relationship of the anlage during development.     

Mercury in blood cells—Altered elemental profiles

The study was composed of 27 persons that displayed vague symptoms similar to those of the victims of Minamata and Iraq. Skew distributions of mercury were observed in individual erythrocytes and neutrophil granulocytes when measured by PIXE. Mercury could not be detected in the platelets. The erythrocytes also displayed lowered concentrations of magnesium and zinc, together with increased concentrations of calcium and strontium. The neutrophils displayed decreased concentrations of magnesium and zinc and increased concentrations of calcium, strontium, and iron. The presence of mercury and the altered elemental profiles in the erythrocytes and the neutrophil granulocytes are suggested as early signs of exposure.     

Single chloride-permeable channels of large conductance in cultured cardiac cells of new-born rats

Large conductance channels were observed in the membrane of cultured cardiac cells of newborn rats studied with the patch-clamp technique in cell-attached and inside-out configurations. These channels were observed in 4% of the patches. In the cell-attached configuration they exhibited outward rectification and partial inactivation. In the inside-out configuration no rectification occurred but inactivation was present, mainly during hyperpolarizations. Two channels with large single unit conductances (400–450 pS) and one with a smaller conductance (200–250 pS) were frequently observed in the same patch. The two large channels generally had different kinetics. Under steady-state conditions the opening probability of the faster channel appeared to be voltage-independent. The slower channel was activated by depolarization. In asymmetrical solutions the permeability ratios P _Na/P _Cl were 0.03 and 0.24 for the larger and smaller channels, respectively; corresponding values for P _Ba/P _Cl were 0.04 and 0.09. It is proposed that in cardiac membranes the chloride permeability system is composed of widely dispersed microclusters forming grouped channels of different types and sizes.     

Rapid lateral diffusion of lectin-labelled glycoconjugates in the human colonic adenocarcinoma cell line HT29

The lateral diffusion of lectin-labelled glycoconjugates was studied in the human colon carcinoma cell line HT29 using fluorescence photobleaching techniques. HT29 cells were grown in either Dulbecco's modified Eagle's medium with glucose (25 mM; DMEM-Glu) or with galactose (25 mM; DMEM-Gal). Cell cultivation in the DMEM-Gal medium was assumed to promote a transformation of the cells to become small-intestinal-like with characteristic microvilli and associated enzymes. The diffusion of glycoconjugates labelled with fluoresceinated Triticum vulgaris agglutinin (Wheat germ agglutinin; WGA), Ricinus communis agglutinin-I (RCA-I), Concanavalia ensiformis agglutinin (ConA), Ulex europaeus agglutinin-I (UEA-I) and Arachis hypogaea agglutinin (PNA) was in all cases rapid, with a diffusion constant (D) ranging between 0.4 and 0.8×10^-8 cm² s^-1. As a comparison the diffusion of the fluorescent synthetic lipid analog diI-C₁₄ was characterized by D=0.8 – 1.0 × 10^–8 cm² s^-1. The diffusion of lectin-labelled surface components could not be related to the presence of microvilli on HT29 cells grown in DMEM-Gal, which ought to yield an apparently lower diffusion rate. The results indicate either that surface glycoconjugates in HT29 cells are dominated by glycolipid, or that the labelled glycoproteins are more or less free to diffuse in the plane of the membrane.     

Fused cells of frog proximal tubule: I. Basic membrane properties

Summary Patch-clamp techniques were used to study a K channel in the cell membrane of MDCK cells. This cell line derives from the kidney of a normal dog, presumably from the distal nephron, a region involved in potassium secretion. The cells were cultured in confluent monolayers and approached from the apical side. The K channel we describe is Ca²⁺ and voltage activated, has a conductance of 221±7 pS, and can be inhibited by 10mm tetraethylammonium and by 1mm quinidine, but not by 4-aminopyridine, nor by 1mm Ba²⁺ added to the outer side. Using the whole-cell configuration, we find that most of the cationic conductance of the membrane is constituted by a K-specific one (maximum K conductance 32.1±3.9 nSvs. a leak conductance of 1.01±0.17 nS). Comparisons of the maximum K conductance with that of a single K channel indicates that an MDCK cell has an average of 145 such channels. The membrane capacity is 24.5±1.4 pF.     

Effects of reagents modifying carboxyl groups on the gating current of the myelinated nerve fiber

Summary K⁺ channels in inside-out patches from hamster insulin tumor (HIT) cells were studied using the patch-clamp technique. HIT cells provide a convenient system for the study of ion channels and insulin secretion. They are easy to culture, form gigaohm seals readily and secrete insulin in response to glucose. The properties of the cells changed with the passage number. For cell passage numbers 48 to 56, five different K⁺-selective channels ranging from 15 to 211 pS in symmetrical 140mm KCl solutions were distinguished. The channels were characterized by the following features: a channel with a conductance (in symmetrical 140mm KCl solutions) of 210 pS that was activated by noncyclic purine nucleotides and closed by H⁺ ions (pH=6.8); a 211 pS channel that was Ca²⁺-activated and voltage dependent; a 185 pS channel that was blocked by TEA but was insensitive to quinine or nucleotides; a 130 pS channel that was activated by membrane hyperpolarization; and a small conductance (15 pS) channel that was not obviously affected by any manipulation. As determined by radioimmunoassay, cells from passage number 56 secreted 917±128 ng/mg cell protein/48 hr of insulin. In contrast, cells from passage number 77 revealed either no channel activity or an occasional nonselective channel, and secreted only 29.4±8.5 ng/mg cell protein/48 hr of insulin. The nonselective channel found in the passage 77 cells had a conductance of 25 pS in symmetrical 140mm KCl solutions. Thus, there appears to be a correlation between the presence of functional K⁺ channels and insulin secretion.