The Effects of Light Irradiation on the Orientation of Microtubules in Seedlings of Avena sativa L. and Pisum sativum L.

The effects of light irradiation on the arrangement of corticalmicrotubules (MTs) were examined in etiolated A vena mesocotylsand coleoptiles, and in Pisum epicotyls. Elongation of A venamesocotyls ceased as a result of irradiation with white lightwithin 1 h. The predominant orientation of MTs became more longitudinalwithin 1 h in epidermal cells and changed from transverse tooblique, after the elongation ceased, in parenchymal cells.Irradiation with red and with blue light also caused cessationof cell elongation and the same changes in the orientation ofMTs. Elongation of Avena coleoptiles ceased as a result of irradiationwith white light within 24 h. The predominant orientation ofMTs became more longitudinal in epidermal cells and changedfrom transverse to oblique in parenchymal cells. The changein orientation of MTs in epidermal cells preceded that in parenchymalcells. In Pisum epicotyls, elongation ceased as a result ofirradiation with white light within 1 h. Although the orientationsof MTs in epidermal cells did not show any remarkable change,those in parenchymal cells changed from transverse to obliqueafter cell elongation ceased. The change in orientation of MTs and the cessation of cell elongationof A vena mesocotyls induced by white-light irradiation wereboth significantly retarded by treatment with IAA. This resultsuggests that IAA is involved in maintaining the transverseorientation of MTs in Avena mesocotyls. (Received February 22, 1989; Accepted August 2, 1989)     

The Natural Philosophy of Plant Form: Cellular Autoreproduction as a Component of a Structural Explanation of Plant Form

A map-L-system is described which simulates the developmentof the two-dimensional patterns of cell walls displayed at thesurfaces of shoot apices of Psilotum nudum. The simulation ofthese cellular patterns commences with the division of a triangularcell and continues until a complete set of ten different cells,including new triangular cells, is formed amongst the descendantsof each merophyte. The triangular cells generated by means ofthis division pathway, P1, are, in their three-dimensional aspect,four-sided apical cells. In the plant, they have the potentialityto support the development of a shoot apex. The generation ofnew triangular cells by pathway P1 therefore seems to be a preconditionfor the branching of the shoot. Observed variations upon thecellular pattern developed by pathway P1 have also been analysed.Two of these variant pathways, P2 and P3, suggest the typesof controls which are required to bring about all three (P1–P3)patterns of cells. These controls may involve the participationof the plant cytoskeleton and may also require an influencefrom the apical cell itself. The triangular shoot apical cellsof Psilotum are autoreproductive cells: that is, at each division,one of the daughters is a new triangular cell, the other daughterhas some other shape. This example of triangular cell autoreproductionand self-maintenance and its relation to organogenesis is discussedin light of the views on reproduction and self-maintenance expressedby Agnes Arber (1950) in her book The natural philosophy ofplant form(Cambridge: Cambridge University Press). Copyright2001 Annals of Botany Company Agnes Arber, apical cell, cell division patterns, computer simulation, cytoskeleton, L-systems, Living Systems Theory, meristems, Psilotum, shoot apex, stem cell     

Cloning of murine glycosyl phosphatidylinositol anchor attachment protein, GPAA1

Glycosyl phosphatidylinositols (GPIs) are usedto anchor many proteins to the cell surface membrane and are utilizedin all eukaryotic cells. GPI anchoring units are attached to proteins via a transamidase reaction mediated by a GPI transamidase complex. Weisolated one of the components of this complex,mGPAA1 (murine GPI anchor attachment), by the signalsequence trap method. mGPAA1 cDNA is about 2 kb in lengthand encodes a putative 621 amino acid protein. The mGPAA1gene has 12 small exons and 11 small introns. mGPAA1 mRNA isubiquitously expressed in mammalian cells, and in situ hybridizationanalysis revealed that it is abundant in the choroid plexus, skeletalmuscle, osteoblasts of rib, and occipital bone in mouse embryos. Itsexpression levels and transamidation efficiency decreased withdifferentiation of embryonic stem cells. The 3T3 cell lines expressingantisense mGPAA1 failed to express GPI-anchored proteins onthe cell surface membrane.

     

Studies on the Development of the Air Pores and Air Chambers of Marchantia paleacea: 1. Light Microscopy

The ontogeny of the air pores and air chambers of Marchantiapaleacea begins with the schizogenous development of protodermalintercellular spaces of the initial apertures, and is completedwith the formation of the air pores and giant sub-epidermalair chambers bearing numerous photosynthetic filaments. Intercellularspace formation commences from the thallus surface and proceedsinwards to the first internal layer of cells. The cells amongwhich spaces develop do not originate from one mother cell.Spaces are formed only in the regions of the intersection ofthe anticlinal walls of three, four, or sometimes more successivederivatives of S₁, S₃ and S₄ segments of the apical cell, oneor two of which have been divided periclinally and the restanticlinally. Protodermal intercellular spaces appear in mostor all the corners of these cells, the anticlinal walls of whichexhibit an opposite disposition. The S₁, S₂, S₃ and S₄ segmentsare produced by definite divisions of a five-sided apical celland by a series of divisions give rise to initial cells of theinternal layers of the thallus and initial cells of the protodermaland sub-protodermal layers. The concept of a quiescent apicalcell cannot be accepted, since dividing apical cells have beenobserved, and the pattern of wall disposition of the thallusapex cannot be explained without the active participation ofthe apical cell. The air chambers are apparently of exogenous origin. They resultfrom the broadening of the bottom of the initial apertures bythe coordination of the rate of anticlinal divisions and growthof the protodermal and sub-protodermal cells surrounding theintercellular spaces of the initial apertures. The ontogenyof the pore rings starts at an advanced stage of air chamberformation not from a mother cell but from the cells which surroundthe closed entrance of the air chamber, by a shift of the planeof division from anticlinal to periclinal. Before the periclinaldivisions a new axis of growth perpendicular to the thallussurface is established in the mother cells of the pore. By a polarized growth into the air chamber followed by periclinaldivisions, the cells of the floor form initial cells of thephotosynthetic filaments. The latter divide again to form singleor branched photosynthetic filaments. Marchantia paleacea, air pore, air chamber     

Proximal tubular epithelial cells are generated by division of differentiated cells in the healthy kidney

We searched for evidence for a contribution of stem cells in growth of the proximal S3 segments of healthy rats. According to the stem cell model, stem cells are undifferentiated and slow cycling; the bulk of cycling cells are transit amplifying, rapidly cycling cells. We show the following. 1) By continuous application of a thymidine analog (ThA) for 7 days, S3 proximal epithelial cells in healthy kidneys display a high-cycling rate. 2) Slow-cycling cells, identified by lack of ThA uptake during 14 days of continuous ThA application up to death and by expression of the cell cycle protein Ki67 at death, have the same degree of differentiation as quiescent cells. 3) To detect rapidly cycling cells, rats were killed at various time points after injection of a ThA. Double immunofluorescence for ThA and a cell cycle marker was performed, with colocalization indicating successive divisions. During one week after division, daughter cells display a very low proliferation rate, indicating the absence of rapidly cycling cells. 4) Labeling with cyclin D1 showed that this low proliferation rate is due to cycle arrest. 5) More than 50% of the S3 cells entered the cell cycle 36 h after a potent proliferative stimulus (lead acetate injection). We conclude that generation of new cells in the proximal tubule relies on division of differentiated, normally slow-cycling cells. These may rapidly enter the cycle under an adequate stimulus. immunohistochemistry; cell cycle; proliferation; renal stem cells; proximal tubule; renal epithelial cells     

Functional interaction of the K-Cl cotransporter (KCC1) with the Na-K-Cl cotransporter in HEK-293 cells

We have studiedthe regulation of the K-Cl cotransporter KCC1 and its functionalinteraction with the Na-K-Cl cotransporter. K-Cl cotransporter activitywas substantially activated in HEK-293 cells overexpressing KCC1(KCC1-HEK) by hypotonic cell swelling, 50 mM external K, andpretreatment with N-ethylmaleimide(NEM). Bumetanide inhibited ⁸⁶Rbefflux in KCC1-HEK cells after cell swelling [inhibition constant (K_i) ~190µM] and pretreatment with NEM(K_i ~60 µM).Thus regulation of KCC1 is consistent with properties of the red cellK-Cl cotransporter. To investigate functional interactions between K-Cland Na-K-Cl cotransporters, we studied the relationship between Na-K-Clcotransporter activation and intracellular Cl concentration([Cl]_i). Without stimulation, KCC1-HEK cells had greater Na-K-Cl cotransporter activitythan controls. Endogenous Na-K-Cl cotransporter of KCC1-HEK cells wasactivated <2-fold by low-Cl hypotonic prestimulation, compared with10-fold activation in HEK-293 cells and >20-fold activation in cellsoverexpressing the Na-K-Cl cotransporter (NKCC1-HEK). KCC1-HEK cellshad lower resting[Cl]_i than HEK-293cells; cell volume was not different among cell lines. We found a steeprelationship between[Cl]_i and Na-K-Clcotransport activity within the physiological range, supporting aprimary role for [Cl]_iin activation of Na-K-Cl cotransport and in apical-basolateral crosstalk in ion-transporting epithelia.     

Growth and mortality of flagellates and non-flagellate cells of Phaeocystis globosa (Prymnesiophyceae)

Two cell types of the same clone of Phaeocystis globosa, solitarynon-flagellate cells and flagellates, were grown in batch culturesunder identical conditions. The non-flagellate cells had a shorterlag phase (1.4 versus 2.8 days) and a higher growth rate (0.72versus 0.65 day^–1) than flagellate cells. The flagellateshad a longer stationary phase (15.6 versus 9.5 days) and a lowerdeath rate (0.07 versus 0.52 day^–1) than non-flagellatecells. All differences were statistically significant. Biomassyield did not differ between the two cell types. The short lagphase and high growth rate of nonflagellate cells correspondsto field observations of rapidly developing non-flagellate Phaeocystisblooms that are typically observed in nutrient-rich environmentssuch as temperate seas in spring. The flagellate cell type,with its longer stationary phase and lower death rate than non-flagellatecells, is better equipped for survival in oligotrophic environments.This explains why the flagellates of Phaeocystis are abundantafter the spring phytoplankton bloom in temperate seas and inother nutrient-poor environments such as the open ocean.     

Isolation and Characterization of the Olfactory Epithelial Cells of the Catfish

A preparation enriched in olfactory receptor cells has beenobtained from the olfactory mucosa of the catfish (Ictaluruspunctatus). The tissue was treated successively with trypsin,DNase, trypsin inhibitor, EDTA in Ca^{+ +} , Mg^{+ +} free mediumaccording to a method derived from that of Cohen, et al.⁽¹⁾.After mechanical disruption of the isolated olfactory lamellae,the cells were isolated by centrifugation on a Ficoll gradient.Each type of cell was morphologically identified by comparingin situ and in vitro preparations by SEM. Small round cellswere collected on 10% Ficoll. The nature of these cells is notknown but part of them are certainly basal cells which havebeen shown⁽²⁾ to be the precursors of the constantly regeneratingolfactory neurons. Respiratory cells settled mainly on 20% Ficoll.A fraction containing 60% sustentacular cells was collectedon 33% Ficoll. Olfactory cells characterized by an axon, a dendriteand several cilia, were found on 37% Ficoll. This fraction alsocontains up to 40% sustentacular cells. A yield of 20% was measuredfor olfactory cell isolation. Vital staining and ability tosynthesize RNA indicate a viability of the final preparationof 70% to 80%. Further identification of the cells was performedby measuring the binding activity of a series of amino acidsto a preparation enriched in olfactory cells. A good correlationwas determined between the extent of the binding and the reportedelectrophysiological activities of these amino acids recordedin vivo. Although the final olfactory cell suspension is notpure, it constitutes the first step in the study of the olfactoryreceptor sites.     

Expression of Genes for Photosynthesis and the Relationship to Salt Tolerance of Alfalfa (Medicago sativa) Cells

The basis for the salt tolerant phenotype of a line of Medicagosativa (alfalfa) cells (HG2-N1) derived by selection from asalt sensitive line (HG2) was studied. The salt tolerant HG2-N1cell line shows eleven fold elevated chlorophyll content overthat of the parent salt sensitive HG2 cell line, with an additionaltwo fold increase in chlorophyll levels when the cells are grownin 1% NaCl. In this study, we demonstrate that the chlorophyllaccumulation and response to salt was associated with largeincreases in the two photosynthesis related mRNAs, rbcL (ribulose-l,5-bis-phosphatecarboxylase [Rubisco] large subunit) and rbcS (Rubisco smallsubunit) and a substantial increase in the activity of the holoenzyme.The salinity-induced increase in catalytically competent Rubiscoprotein in the salt tolerant cell line was highly responsiveto light and correlated with the salt tolerant phenotype. Inaddition, NaCl stimulated rbcL and rbcS mRNA and Rubisco accumulationin dark grown salt tolerant cells, indicating that salt couldsubstitute to some degree for light in stimulating increasesin specific mRNA and protein concentrations. Increased photosyntheticcompetence associated with these increased protein levels wasapparently important in contributing to the salt tolerant phenotypeof HG2-N1, since PS II electron transport inhibitors (DCMU,cyanazine) were found to significantly reduce the growth ofthis cell line in the presence of salt, but not in the absenceof salt. These results suggest that the salt-induced increasein mRNA and protein accumulation involved in photosynthesismay play a significant role in the salt tolerant capabilityof HG2-N1 alfalfa cells. (Received April 2, 1990; Accepted September 10, 1990)     

Flow Cytometric Determination of Relative Nuclear DNA Contents in Bicellulate and Tricellulate Pollen

Nuclear DNA content in mature pollen was measured with a flowcytometer Pollen of Lilium longiflorum, Dendranthema grandiflora(syn Chrysanthemum monfolium) and Zea mays was chopped and stainedwith the DNA fluorochrome DAPI DNA levels, expressed as arbitraryC values, were compared with those of nuclei isolated from leafor root material of the same plants In mature tricellulate pollen the generative cell is dividedafter second pollen mitosis into two sperm cells Tricellulatepollen from maize and chrysanthemum gave rise to one large 1Cpeak and, only in the case of chrysanthemum, a much smallerone at the 2C level These results suggest that the haploid nucleiof the vegetative as well as both sperm cells in tricellulatepollen are arrested in the G₁ stage of nuclear division Thesmall 2C peak in the case of chrysanthemum probably arose froma fraction of pollen with the sporophytic chromosome number(2n pollen) In contrast to this, mature bicellulate lily pollengave rise to two identical peaks at the 1C and the 2C levelFrom this result it was concluded that in bicellulate pollen,the 1C peak is caused by the signal of the haploid vegetativenucleus arrested in the G₁ stage of nuclear division, whereasthe 2C peak originates from the haploid generative nucleus whichhas already undergone DNA synthesis and is arrested in G₂ Lilium longiflorumThunb, lily, Dendranthema grandiflora Tzelev (syn Chrysanthemum morifolium Ramat ), chrysanthemum, Zea maysL, maize, male gametophytic cells, vegetative cells, generative cells, sperm cells, unreduced pollen, sporophytic cells, relative nuclear DNA contents, replication stage     

Effects of soil resistance to root penetration on leaf expansion in wheat (Triticum aestivum L.): kinematic analysis of leaf elongation

Wheat leaves (Triticum aestivum L.) elongated 50% more slowlywhen plants were grown in soils with high mechanical resistanceto penetration (R_s. The profiles of epidermal cell lengths alongthe growth zone of expanding leaves and the locations of newlyformed walls were recorded in order to compare the kineticsof elongation and partitioning of both meristematic and non-meristematiccells. In leaf 5, which completely developed under stress, highR_s, did not affect the flux of mature cells through the elongationzone; leaf elongation was reduced only because these cells wereshorter. This reduced size reflected a reduction in cell lengthat partitioning, associated with shorter cycling time. The relativerates of cell elongation before and after partitioning wereunchanged. Cell fluxes were similar because the population ofmeristematic cells was reduced, offsetting their increased partitioningrate. In contrast, in leaf 1, high R_s, had no effect on thenumber of dividing cells; elongation rate was reduced becauseof slower relative cell expansion rate and slower cell partitioningrate. These differences could reflect differences in the stageat which successive leaves perceived root stress and also time-dependentchanges in the responsiveness of leaf development to stress-inducedroot signals or in the nature of these signals. The data reveal that cell cycling time may in fact be decreasedby unfavourable growth conditions and is not directly relatedto cell expansion rates; they also show that the elongationrate of meristematic cells is partly independently controlledfrom that of non-meristematic cells. Key words: Wheat, kinematics of leaf expansion, cell partitioning, cell elongation, root impedance     

Caco-2 intestinal cell differentiation is associated with G1 arrest and suppression of CDK2 and CDK4

The cellular mechanisms regulating intestinal proliferation anddifferentiation remain largely undefined. Previously, we showed anearly induction of the cyclin-dependent kinase (CDK) inhibitor p21^Waf1/Cip1 in Caco-2 cells, ahuman colon cancer line that spontaneously differentiates into a smallbowel phenotype. The purpose of our present study was to assess thetiming of cell cycle arrest in relation to differentiation in Caco-2cells and to examine the mechanisms responsible for CDK inactivation.Caco-2 cells undergo a relativeG₁/S block and cease toproliferate at day3 postconfluency; an increase in theactivity of terminally differentiated brush-border enzymes (sucrase andalkaline phosphatase) was noted at day6 postconfluency. Cell cycle block wasassociated with suppression of both CDK2 and CDK4 activities, which areimportant for G₁/S progression.Treatment of the CDK immune complexes with the detergent deoxycholate(DOC) resulted in restoration of CDK2, but not CDK4, activity atday 3 postconfluency, suggesting the presence of inhibitory protein(s)binding to the cyclin/CDK2 complex at this time point. An increasedbinding of p21^Waf1/Cip1 to CDK2complexes at day3 postconfluency was noted, suggesting a potential role for p21^Waf1/Cip1in CDK2 inactivation; however, immunodepletion ofp21^Waf1/Cip1 from Caco-2 proteinextracts demonstrated thatp21^Waf1/Cip1 is only partiallyresponsible for CDK2 suppression atday 3 postconfluency. A decrease in the cyclin E/CDK2 complex appears tocontribute to the CDK2 inactivation noted atdays6 and12 postconfluency. Taken together, ourresults suggest that multiple mechanisms contribute to CDK suppressionduring Caco-2 cell differentiation. Inhibition of CDK2 and CDK4 leadsto G₁ arrest and inhibition ofproliferation that precede Caco-2 cell differentiation.

     

Inhibitory effect of lycorine on cell division and cell elongation

Lycorine, an alkaloid isolated from bulbs of Amarillidaceae,was found to be a powerful inhibitor of cell division and elongation.Adding different concentrations of lycorine from 10^–6M to 10^–4 M in an appropriate growth-medium strongly inhibitedcell division in explants of lettuce pith parenchyma. The sameresult was obtained with liquid yeast cultures growing exponentially. Lycorine-treated meristematic cells of the primary roots ofVicia faba also showed rapid inhibition of the mitotic indexwhile interphase cells increased proportionately. Lycorine alsoinhibited endogenous and auxin-induced cell elongation in Avenacoleoptiles and pea segments. Since both cell division and cell elongation require proteinsynthesis and RNA synthesis, the assumption is that lycorineprobably inhibits one of the two syntheses. ¹This study was supported by a contract between the NationalResearch Council of Italy and University of Bari, Instituteof Botany. (Received November 27, 1972; )     

Relationship Between Root Morphogenesis and Period of Predominant Cell Arrest in Intact and Aseptically-cultured Roots of Helianthus annuus L.

Root morphogenesis and cell cycle kinetics of intact and aseptically-grownexcised roots of Helianthus annuus L. were studied. Intact rootsshow predominant cell arrest in G1 with an absence of polyploidcells coincident with secondary vascularization. Exposure ofthe cut ends of aseptically grown excised roots to known concentrationsof indol-3-yl acetic acid, benzyladenine, and myo-inositol for8 weeks initiated the production of secondary vascular tissuesand predominant cell arrest in G2 concommitant with poiyploidization.Excised roots grown in the absence of these substances producedroots with only primary vascularization and predominant cellarrest in G1 coincident with an absence of polyploidization.These results indicate that (a) root cells of H. annuus havethe ability to undergo polyploidization that may be inducedby exogeneously applied chemicals, (b) a general relationshipbetween predominant cell arrest in G1 coincident with the absenceof secondary vascularization does not hold true and (c) althoughsecondary vascularization occurs in cultured roots exposed toall three additives similar to secondary vascularization inintact roots, the two roots should not be considered identicalin all respects. Helianthus annus L., sunflower, root, morphogenesis, cell cycle kinetics, polyploidy, cell differentiation, vascularization     

Periodic Gene Expression Patterns during the Highly Synchronized Cell Nucleus and Organelle Division Cycles in the Unicellular Red Alga Cyanidioschyzon merolae

Previous cell cycle studies have been based on cell-nuclearproliferation only. Eukaryotic cells, however, have double membranes-boundorganelles, such as the cell nucleus, mitochondrion, plastidsand single-membrane-bound organelles such as ER, the Golgi body,vacuoles (lysosomes) and microbodies. Organelle proliferations,which are very important for cell functions, are poorly understood.To clarify this, we performed a microarray analysis during thecell cycle of Cyanidioschyzon merolae. C. merolae cells containa minimum set of organelles that divide synchronously. The nuclear,mitochondrial and plastid genomes were completely sequenced.The results showed that, of 158 genes induced during the S orG2-M phase, 93 were known and contained genes related to mitochondrialdivision, ftsZ1-1, ftsz1-2 and mda1, and plastid division, ftsZ2-1,ftsZ2-2 and cmdnm2. Moreover, three genes, involved in vesicletrafficking between the single-membrane organelles such as vps29and the Rab family protein, were identified and might be relatedto partitioning of single-membrane-bound organelles. In othergenes, 46 were hypothetical and 19 were hypothetical conserved.The possibility of finding novel organelle division genes fromhypothetical and hypothetical conserved genes in the S and G2-Mexpression groups is discussed.     

Cell Cycle Changes in the Shoot Apex of Silene coeli-rosa During the Second and Third Days of Floral Induction

The cell cycle in Silene coeli-rosa shoot apices was measuredto test whether or not early components of the floral stimulus,produced during the 2nd and 3rd long days (LD) of an inductiveLD treatment, resulted in an increase in the duration of G₂phase in constant 20–24 h cell cycles. Plants were grownat 20°C in short days (SD) of 8 h light and 16 h darknessfor 28 d (day 0). Starting on day 0, plants were given SD or3 LD each comprising an identical 8 h day and 16 h photo-extension,or 3 dark-interrupted (d.i.) non-inductive LD, interrupted at1700 h of each day with 1 h of darkness. The cell cycle (percentagelabelled mitoses method) and changes in cell number were determinedin the shoot apical meristem. During days 1–2 of the SDtreatment, the cell cycle and mean cell generation time (MCGT)was 18 and 32 h, respectively, giving a growth fraction of 56%.During days 2–3, the cell cycle and MCGT shortened to15 and 23 h, respectively (growth fraction = 65%). During days1–2 of the LD and d.i. LD treatments, cell cycles andMCGTs were 9–10 and 27–29 h, respectively, resultingin smaller growth fractions (about 33%). Thus, shortened cellcycles and altered growth fractions occurred regardless of whetheror not the treatment was inductive. The LD treatment resultedin a marked shortening of G₁ and, to a lesser extent, S-phase,whilst G₂ remained constant. These changes were consistent withincreases in the proportion of cells in G₂ during the photoextensionof each LD which were suppressed during the comparable periodsof the d.i. LD treatment. The latter treatment resulted in eachphase occupying virtually identical proportions of the cellcycle as in the SD treatment. Thus, the unique cell cycle responsesto the initial part of the inductive LD treatment were increasesin the proportion of cells in G₂ coupled with G₁ and G₂ beingof similar duration. Cell cycle, mean cell generation time, shoot apex, Silene coeli-rosa     

SYNCHRONIZATION OF BACTERIAL CULTURE BY PREINCUBATION OF CELLS AT HIGH CELL DENSITY

The growth of Escherichia coli strain B in a liquid medium wasfound to cease at a cell density of 5x10⁹ cells per ml. (Thiscritical concentration is designated as the maximum or M-concentration.)Even cells harvested from the logarithmic growth phase couldnot divide at this or higher cell densities. Investigationson the metabolic activities of such cultures, however, showedthat the synthesis of cellular protein and nucleic acid wastaking place under such circumstances, showing that only someprocess (or processes) particularly related to cell divisionwas suppressed at the critical cell concentration in question. This finding led us to devise a new method of synchronizationof E. coli: cells harvested from a logarithmic phase were preincubatedat the critical concentration of 5x10⁹ cells per ml for 45 minutes,and then diluted 100 times with fresh medium. This led to synchronizationof cell division, as shown by a stepwise multiplication in cellnumber. (Received June 20, 1961; )     

Modulation of K+ currents in monocytes by VCAM-1 and E-selectin on activated human endothelium

Resting membrane potential (RMP) and whole cell currents wererecorded in human THP-1 monocytes adherent to polystyrene, unstimulated human umbilical vein endothelial cells (HUVECs),lipopolysaccharide (LPS)-treated HUVECs, immobilizedE-selectin, or vascular cell adhesion molecule 1 (VCAM-1)using the patch-clamp technique. RMP after 5 h on polystyrene was24.3 ± 1.7 mV (n = 42) with delayed rectifier K⁺(I_dr) andCl currents(I_Cl) presentin >75% of the cells. Inwardly rectifying K⁺ currents(I_ir) werepresent in only 14% of THP-1 cells. Adherence to unstimulated HUVECsor E-selectin for 5 h had no effect on I_ir orI_Cl but decreasedI_dr. Five hoursafter adherence to LPS-treated HUVECs, outward currents were unchanged,but I_ir waspresent in 81% of THP-1 cells. A twofold increase inI_ir and ahyperpolarization (41.3 ± 3.7 mV,n = 16) were abolished by pretreatmentof THP-1 cells with cycloheximide, a protein synthesis inhibitor, orherbimycin A, a tyrosine kinase inhibitor, or by pretreatment of theLPS-treated HUVECs with anti-VCAM-1. Only a brief (15-min) interactionbetween THP-1 cells and LPS-treated HUVECs was required toinduce I_ir expression 5 h later. THP-1 cells adherent to VCAM-1 exhibited similarconductances to cells adherent to LPS-treated HUVECs. Thus engagementof specific integrins results in selective modulation of differentK⁺ conductances.