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Starvation effect on the morphology of microvilli in HeLa cells. Biochem Biophys Res Commun 2019; 514:1238-1243. [DOI: 10.1016/j.bbrc.2019.05.073] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2019] [Accepted: 05/09/2019] [Indexed: 01/03/2023]
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Lange K. Fundamental role of microvilli in the main functions of differentiated cells: Outline of an universal regulating and signaling system at the cell periphery. J Cell Physiol 2010; 226:896-927. [PMID: 20607764 DOI: 10.1002/jcp.22302] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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Lange K. Role of microvillar cell surfaces in the regulation of glucose uptake and organization of energy metabolism. Am J Physiol Cell Physiol 2002; 282:C1-26. [PMID: 11742794 DOI: 10.1152/ajpcell.2002.282.1.c1] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Experimental evidence suggesting a type of glucose uptake regulation prevailing in resting and differentiated cells was surveyed. This type of regulation is characterized by transport-limited glucose metabolism and depends on segregation of glucose transporters on microvilli of differentiated or resting cells. Earlier studies on glucose transport regulation and a recently presented general concept of influx regulation for ions and metabolic substrates via microvillar structures provide the basic framework for this theory. According to this concept, glucose uptake via transporters on microvilli is regulated by changes in the structural organization of the microfilament bundle, which is acting as a diffusion barrier between the microvillar tip compartment and the cytoplasm. Both microvilli formation and the switch of glucose metabolism from "metabolic regulation" to "transport limitation" occur during differentiation. The formation of microvillar cell surfaces creates the essential preconditions to establish the characteristic functions of specialized tissue cells including the coordination between glycolysis and oxidative phosphorylation, regulation of cellular functions by external signals, and Ca(2+) signaling. The proposed concept integrates various aspects of glucose uptake regulation into a ubiquitous cellular mechanism involved in regulation of transmembrane ion and substrate fluxes.
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Lange K, Gartzke J. Microvillar cell surface as a natural defense system against xenobiotics: a new interpretation of multidrug resistance. Am J Physiol Cell Physiol 2001; 281:C369-85. [PMID: 11443036 DOI: 10.1152/ajpcell.2001.281.2.c369] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The phenomenon of multidrug resistance (MDR) is reinterpreted on the basis of the recently proposed concept of microvillar signaling. According to this notion, substrate and ion fluxes across the surface of differentiated cells occur via transporters and ion channels that reside in membrane domains at the tips of microvilli (MV). The flux rates are regulated by the actin-based cytoskeletal core structure of MV, acting as a diffusion barrier between the microvillar tip compartment and the cytoplasm. The expression of this diffusion barrier system is a novel aspect of cell differentiation and represents a functional component of the natural defense system of epithelial cells against environmental hazardous ions and lipophilic compounds. Because of the specific organization of epithelial Ca(2+) signaling and the secretion, lipophilic compounds associated with the plasma membrane are transferred from the basal to the apical cell surface by a lipid flow mechanism. Drug release from the apical pole occurs by either direct secretion from the cell surface or metabolization by the microvillar cytochrome P-450 system and efflux of the metabolites and conjugation products through the large multifunctional anion channels localized in apical MV. The natural microvillar defense system also provides a mechanistic basis of acquired MDR in tumor cells. The microvillar surface organization is lost in rapidly growing cells such as tumor or embryonic cells but is restored during exposure of tumor cells to cytotoxins by induction of a prolonged G(0)/G(1) resting phase.
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Affiliation(s)
- K Lange
- Bundesanstalt für Arbeitsschutz und Arbeitsmedizin, D-10317 Berlin, Germany
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Abstract
The recently presented theory of microvillar Ca(2+)signaling [Lange, K. (1999) J. Cell. Physiol.180, 19-35], combined with Manning's theory of "condensed counterions" in linear polyelectrolytes [Manning, G. S. (1969). J. Chem. Phys.51, 924-931] and the finding of cable-like ion conductance in actin filaments [Lin, E. C. & Cantiello, H. F. (1993). Biophys. J.65, 1371-1378], allows a systematic interpretation of the role of the actin cytoskeleton in ion channel regulation. Ion conduction through actin filament bundles of microvilli exhibits unique nonlinear transmission properties some of which closely resemble that of electronic semiconductors: (1) bundles of microfilaments display significant resistance to cation conduction and (2) this resistance is decreased by supply of additional energy either as thermal, mechanical or electromagnetic field energy. Other transmission properties, however, are unique for ionic conduction in polyelectrolytes. (1) Current pulses injected into the filaments were transformed into oscillating currents or even into several discrete charge pulses closely resembling that of single-channel recordings. Discontinuous transmission is due to the existence of counterion clouds along the fixed anionic charge centers of the polymer, each acting as an "ionic capacitor". (2) The conductivity of linear polyelectrolytes strongly decreases with the charge number of the counterions; thus, Ca(2+)and Mg(2+)are effective modulator of charge transfer through linear polyelectrolytes. Field-dependent formation of divalent cation plugs on either side of the microvillar conduction line may generate the characteristic gating behavior of cation channels. (3) Mechanical movement of actin filament bundles, e.g. bending of hair cell microvilli, generates charge translocations along the filament structure (mechano-electrical coupling). (4) Energy of external fields, by inducing molecular dipoles within the polyelectrolyte matrix, can be transformed into mechanical movement of the system (electro-mechanical coupling). Because ionic transmission through linear polyelectrolytes is very slow compared with electronic conduction, only low-frequency electromagnetic fields can interact with the condensed counterion systems of linear polyelectrolytes. The delineated characteristics of microvillar ion conduction are strongly supported by the phenomenon of electro-mechanical coupling (reverse transduction) in microvilli of the audioreceptor (hair) cells and the recently reported dynamics of Ca(2+)signaling in microvilli of audio- and photoreceptor cells. Due to the cell-specific expression of different types and combinations of ion channels and transporters in the microvillar tip membrane of differentiated cells, the functional properties of this cell surface organelle are highly variable serving a multitude of different cellular functions including receptor-mediated effects such as Ca(2+)signaling, regulation of glucose and amino acid transport, as well as modulation of membrane potential. Even mechanical channel activation involved in cell volume regulation can be deduced from the systematic properties of the microvillar channel concept. In addition, the specific ion conduction properties of microfilaments combined with their proposed role in Ca(2+)signaling make microvilli the most likely cellular site for the interaction with external electric and magnetic fields.
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Affiliation(s)
- K Lange
- Kladower Damm 25b, 14089 Berlin, Germany.
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Abstract
A novel mechanism of cellular volume regulation is presented, which ensues from the recently introduced concept of transport and ion channel regulation via microvillar structures (Lange K, 1999, J Cell Physiol 180:19-35). According to this notion, the activity of ion channels and transporter proteins located on microvilli of differentiated cells is regulated by changes in the structural organization of the bundle of actin filaments in the microvillar shaft region. Cells with microvillar surfaces represent two-compartment systems consisting of the cytoplasm on the one side and the sum of the microvillar tip (or, entrance) compartments on the other side. The two compartments are separated by the microvillar actin filament bundle acting as diffusion barrier ions and other solutes. The specific organization of ion and water channels on the surface of microvillar cell types enables this two-compartment system to respond to hypo- and hyperosmotic conditions by activation of ionic fluxes along electrochemical gradients. Hypotonic exposure results in swelling of the cytoplasmic compartment accompanied by a corresponding reduction in the length of the microvillar diffusion barrier, allowing osmolyte efflux and regulatory volume decrease (RVD). Hypertonic conditions, which cause shortening of the diffusion barrier via swelling of the entrance compartment, allow osmolyte influx for regulatory volume increase (RVI). Swelling of either the cytoplasmic or the entrance compartment, by using membrane portions of the microvillar shafts for surface enlargement, activates ion fluxes between the cytoplasm and the entrance compartment by shortening of microvilli. The pool of available membrane lipids used for cell swelling, which is proportional to length and number of microvilli per cell, represents the sensor system that directly translates surface enlargements into activation of ion channels. Thus, the use of additional membrane components for osmotic swelling or other types of surface-expanding shape changes (such as the volume-invariant cell spreading or stretching) directly regulates influx and efflux activities of microvillar ion channels. The proposed mechanism of ion flux regulation also applies to the physiological main functions of epithelial cells and the auxiliary action of swelling-induced ATP release. Furthermore, the microvillar entrance compartment, as a finely dispersed ion-accessible peripheral space, represents a cellular sensor for environmental ionic/osmotic conditions able to detect concentration gradients with high lateral resolution. Volume regulation via microvillar surfaces is only one special aspect of the general property of mechanosensitivity of microvillar ionic pathways.
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Abstract
Proceeding from the recent finding that the main components of the Ca++ signal pathway are located in small membrane protrusions on the surface of differentiated cells, called microvilli, a novel concept of cellular Ca++ signaling was developed. The main features of this concept can be summarized as follows: Microvilli are formed on the cell surface of differentiating or resting cells from exocytic membrane domains, growing out from the cell surface by elongation of an internal bundle of actin filaments. The microvillar tip membranes contain all functional important proteins synthesized such as ion channels and transporters for energy-providing substrates and structural components, which are, in rapidly growing undifferentiated cells, distributed over the whole cell surface by lateral diffusion. The microvillar shaft structure, a bundle of actin filaments, forms a dense cytoskeletal matrix tightly covered by the microvillar lipid membrane and represents an effective diffusion barrier separating the microvillar tip compartment (entrance compartment) from the cytoplasm. This diffusion barrier prevents the passage of low molecular components such as Ca++ glucose and other relevant substrates from the entrance compartment into the cytoplasm. The effectiveness of the actin-based diffusion barrier is modulated by various signal pathways and effectors, most importantly, by the actin-depolymerizing/reorganizing activity of the phospholipase C (PLC)-coupled Ca++ signaling. Moreover, the microvillar bundle of actin filaments plays a dual role in Ca++ signaling. It combines the function of a diffusion barrier, preventing Ca++ influx into the resting cell, with that of a high-affinity, ATP-dependent, and IP3-sensitive Ca++ store. Activation of Ca++ signaling via PLC-coupled receptors simultaneously empties Ca++ stores and activates the influx of external Ca++. The presented concept of Ca++ signaling is compatible with all established data on Ca++ signaling. Properties of Ca++ signaling, that could not be reconciled with the basic principles of the current hypothesis, are intrinsic properties of the new concept. Quantal Ca++ release, Ca(++)-induced Ca++ release (CICR), the coupling phenomen between the filling state of the Ca++ store and the activity of the Ca++ influx pathway, as well as the various yet unexplained complex kinetics of Ca++ uptake and release can be explained on a common mechanistic basis.
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Lange K, Brandt U, Gartzke J, Bergmann J. Action of insulin on the surface morphology of hepatocytes: role of phosphatidylinositol 3-kinase in insulin-induced shape change of microvilli. Exp Cell Res 1998; 239:139-51. [PMID: 9511732 DOI: 10.1006/excr.1997.3894] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
In previous studies we have shown that the insulin-responding glucose transporter isoform of 3T3-L1 adipocytes, GluT4, is almost completely located on microvilli. Furthermore, insulin caused the integration of these microvilli into the plasma membrane, suggesting that insulin-induced stimulation of glucose uptake may be due to the destruction of the cytoskeletal diffusion barrier formed by the actin filament bundle of the microvillar shaft regions [Lange et al. (1990) FEBS Lett. 261, 459-463; Lange et al. (1990) FEBS Lett. 276, 39-41]. Similar shape changes in microvilli were observed when the transport rates of adipocytes were modulated by glucose feeding or starvation. Here we demonstrate that the action of insulin on the surface morphology of hepatocytes is identical to that on 3T3L1 adipocytes; small and narrow microvilli on the surface of unstimulated hepatocytes were rapidly shortened and dilated on top of large domed surface areas. The aspect and mechanism of this effect are closely related to "membrane ruffling" induced by insulin and other growth factors. Pretreatment of hepatocytes with the PI 3-kinase inhibitor wortmannin (100 nM), which completely prevents transport stimulation by insulin in adipocytes and other cell types, also inhibited insulin-induced shape changes in microvilli on the hepatocyte surface. In contrast, vasopressin-induced microvillar shape changes in hepatocytes [Lange et al. (1997) Exp. Cell Res. 234, 486-497] were insensitive to wortmannin pretreatment. These findings indicate that PI 3-kinase products are necessary for stimulation of submembrane microfilament dynamics and that cytoskeletal reorganization is critically involved in insulin stimulation of transport processes. The mechanism of the insulin-induced cytoskeletal reorganization can be explained on the basis of the recent finding of Lu et al. [Biochemistry 35(1996) 14027-14034] that PI 3-kinase products exhibit much higher affinity for the profilin-actin complex than the primary products, PIP and PIP2. Thus, activated PI 3-kinase may direct a flux of profilin-actin complexes to the membrane locations of activated insulin receptors, where, due to the release of actin monomers after binding of profilactin to PI(3,4)P2 and PI(3,4,5)P3, massive actin polymerization is initiated. As a consequence, PI 3-kinase activation initiates a vectorial reorganization of the cellular actin system to membrane sites neighboring activated insulin receptors, giving rise to local membrane stress as visualized by extensive surface deformations and shortening of microvilli. In addition, extensive high-affinity binding of F-actin-barbed endcapping proteins enhances the cytoplasmic concentration of rapidly polymerizing filament ends. Consequently, the actin monomer concentration is lowered and the (cytoplasmic) pointed ends of the microvillar shaft bundle depolymerize and become shorter. The observations presented strengthen the previously postulated diffusion-barrier concept of glucose- and ion-uptake regulation and provide a mechanistic basis for explaining the action of insulin and other growth factors on transport processes across the plasma membrane.
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Affiliation(s)
- K Lange
- Institut für Pharmakologie, Freie Universität Berlin, Germany
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Lange J, Schlieps K, Lange K, Knoll-Köhler E. Activation of calcium signaling in isolated rat hepatocytes is accompanied by shape changes of microvilli. Exp Cell Res 1997; 234:486-97. [PMID: 9260919 DOI: 10.1006/excr.1997.3652] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Preceding studies using the hamster insulinoma cell line, HIT, and isolated rat hepatocytes have shown that two essential components of the Ca2+ signaling pathway, the ATP-dependent Ca2+ store and the store-coupled Ca2+ influx pathway, are both located in microvilli covering the surface of these cells. Microvilli-derived vesicles from both cell types exhibited anion and cation pathways which could be inhibited by anion and cation channel-specific inhibitors. These findings suggested that the microvillar tip compartment forms a space which is freely accessible for external Ca2+, ATP, and IP3. The entry of Ca2+ into the cytoplasm, however, is largely restricted by the microvillar core structure, the dense bundle of actin microfilaments acting as a diffusion barrier between the microvillar tip compartment and the cell body. Moreover, evidence has been presented that F-actin may function as ATP-dependent and IP3-sensitive Ca2+ store that can be emptied by profilin-induced depolymerization or reorganization [K. Lange and U. Brandt (1996) FEBS Lett. 395, 137-142]. Here we demonstrate the tight connection between microvillar shape changes and the activation of the Ca2+ signaling system in isolated rat hepatocytes. Using a combination of scanning electron microscopy (SEM) and fura-2 fluorescence technique, we confirmed a consequence of the "diffusion barrier" concept of Ca2+ signaling: Irrespective of the type of the applied stimulus, activation of the Ca2+ influx pathway is accompanied by changes in the structural organization of microvilli indicative of the loss of their diffusion barrier function. We further show that the cell surfaces of unstimulated hepatocytes isolated by either the collagenase or the EDTA perfusion technique are densely covered with microvilli predominantly of a short and slender type. Beside this rather uniformly shaped type of microvilli, a number of dilated surface protrusions were observed. Under these conditions the cells displayed the well known rather high basal [Ca2+]i of 200-250 nM as repeatedly demonstrated for freshly isolated hepatocytes. However, addition of the serine protease inhibitor, phenylmethanesulfonyl fluoride (PMSF), to the cell suspension immediately after its preparation reduced the basal cytoplasmic Ca2+ level to about 100 nM. Concomitantly, dilated surface protrusions disappeared, and cell surfaces exclusively displayed short, slender microvilli. Activation of the Ca2+ signaling pathway by vasopressin, as well as by the IP3-independent acting Ca2+ store inhibitor, thapsigargin, was accompanied by a conspicuous shortening and dilation of microvilli following the same time courses as the respective increases of [Ca2+]i induced by the effectors. Furthermore, the abundance of the large form of surface protrusions on isolated hepatocytes positively correlated with the size of a cellular Ca2+/Fura-2 compartment which is rapidly depleted from Ca2+ by extracellular EGTA. These findings support the postulated localization of the store-coupled Ca2+ influx pathway in microvilli of HIT cells also for hepatocytes and are in accord with the notion of a cytoskeletal diffusion barrier regulating the flux of external Ca2+ via the microvillar tip region in the cytoplasm.
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Affiliation(s)
- J Lange
- Institut für Pharmakologie, Freie Universität Berlin, Germany
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Gartzke J, Lange K, Brandt U, Bergmann J. A new concept for risk assessment of the hazards of non-genotoxic chemicals--electronmicroscopic studies of the cell surface. Evidence for the action of lipophilic chemicals on the Ca2+ signaling system. THE SCIENCE OF THE TOTAL ENVIRONMENT 1997; 199:213-226. [PMID: 9200866 DOI: 10.1016/s0048-9697(97)05498-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Recently, we presented evidence for the localization of components of the cellular Ca2+ signaling pathway in microvilli. On stimulation of this pathway, microvilli undergo characteristic morphological changes which can be detected by scanning electron microscopy (SEM) of the cell surface. Here we show that both receptor-mediated (vasopressin) and unspecific stimulation of the Ca2+ signaling system by the lipophilic tumor promoters thapsigargin (TG) and phorbolmyristateacetate (PMA) are accompanied by the same type of morphological changes of the cell surface. Since stimulated cell proliferation accelerates tumor development and sustained elevation of the intracellular Ca2+ concentrations is a precondition for stimulated cell proliferation, activated Ca2+ signaling is one possible mechanism of non-genomic tumor promotion. Using isolated rat hepatocytes we show that all tested lipophilic chemicals with known tumor promoter action, caused characteristic microvillar shape changes. On the other hand, lipophilic solvents that were used as differentiating agents in cell cultures such as dimethylsulfoxide (DMSO) and dimethylformamide also, failed to change the microvillar shapes. Instead DMSO stabilized the original appearance of microvilli. The used technique provides a convenient method for the evaluation of non-genomic carcinogenicity of chemicals prior to their industrial application.
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Affiliation(s)
- J Gartzke
- Federal Institute for Occupational Safety and Health, Berlin, Germany
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Lange K, Brandt U. Calcium storage and release properties of F-actin: evidence for the involvement of F-actin in cellular calcium signaling. FEBS Lett 1996; 395:137-42. [PMID: 8898081 DOI: 10.1016/0014-5793(96)01025-3] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Preceding studies have shown that the bulk of the ATP-dependent, inositol 1,4,5-trisphosphate (IP3)-sensitive Ca2+ store of hamster insulinoma (HIT) cells is located in microvilli on the cell surface. Similar results were obtained with isolated rat hepatocytes. Moreover, in vesicles of microvillar origin, passive fluxes of Ca2+, ATP, and IP3 occur through cation and anion channels, respectively, suggesting that Ca2+ storage is due to ATP-dependent Ca2+ binding to an intravesicular component. Here we demonstrate that F-actin may be a possible candidate for this function. ATP-actin monomers bind Ca2+ with high affinity (Kd = 2-8 nM) to their divalent cation binding sites. Polymerization of actin monomers decreases the rate constant for divalent cation exchange at this binding site by more than 3 orders of magnitude rendering bound cations nearly unavailable. F-actin-bound Ca2+ can be released by depolymerization and dissociation from Ca(2+)-ADP-actin monomers (Kd = 375 nM). We now provide additional evidence for the possible involvement of actin in Ca2+ storage. (1) Preincubation of surface-derived Ca(2+)-storing vesicles from HIT cells with the F-actin stabilizer, phalloidin, strongly inhibited ATP-dependent Ca2+ uptake, reducing the IP3-sensitive Ca2+ pool by 70%. Phalloidin, when added after the loading process, affected neither the amount of stored Ca2+ nor IP3 action on the store. (2) F-actin polymerized in the presence of Mg2+ in nominally Ca(2+)-free buffer still contained about half of the high affinity sites occupied with Ca2+ (Mg/Ca-F-actin). (3) Using the fura-2 technique, we found that in the presence of ATP, Mg/Ca-F-actin incorporated free Ca2+ at a relatively low rate. Short pulses of ultrasound (3-10 s) strongly accelerated Ca2+ uptake, decreasing free Ca2+ from 500 nM to below 100 nM. (4) In the presence of physiological levels of Mg2+ (0.5 mM), sonication liberated large amounts of Ca2+ from Mg/Ca-F-actin. (5) Ca-F-actin released bound Ca2+ at a very slow rate. Short ultrasonic pulses rapidly elevated free Ca2+ from about 50 nM up to 500 nM. (6) Small amounts of profilin, an actin-binding protein, released Ca2+ both from Ca- and Mg/Ca-F-actin and also inhibited uptake of Ca2+ into Mg/Ca-F-actin. (7) Phalloidin completely inhibited Ca-uptake into Mg/Ca-F-actin even during ultrasonic treatment. These findings suggest that Ca2+ storage may occur by addition of Ca-ATP-actin monomers to reactive ends of the polymer and emptying of this store by profilin-stimulated release of Ca-ADP-actin. Thus, receptor-operated Ca2+ signaling, initiated by phospholipase C activation, may proceed via the well-known phosphatidylinositol phosphate-regulated profilin/gelsolin pathway of actin reorganization/depolymerization. The importance of the proposed microvillar Ca2+ signaling system for living cells remains to be established.
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Affiliation(s)
- K Lange
- Institut für Pharmakologie, Freie Universität Berlin, Germany
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Shepard TH, Park HW. Neural plate microvillus lengthening in rat embryos grown in various concentrations of glucose and further studies of the mechanism. TERATOLOGY 1994; 50:340-7. [PMID: 7716741 DOI: 10.1002/tera.1420500505] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Glucose is an important cellular nutrient, and in the early embryo, which is dependent mostly on anaerobic glycolysis, it is even more essential. Based on tissue culture cells in which glucose utilization has become membrane-limited, a concept has been developed that the tip of the microvilli is the entrance compartment for glucose and that the shaft sets up a diffusion barrier. An increase in length of the microvillus is associated with decreased entry of phosphorylated hexose into the cells. Our previous findings of lengthening of the microvilli of the neural plate cells after 40 min exposure to glucose at room temperature have been extended to a 17 hr whole embryo culture system. In cultures where the final concentration of glucose was 20 and 24 mg/dl there was embryonic death. In those cultures ending with 29-137 mg/dl of glucose the embryos developed normally. Those grown in dialyzed serum supplemented with B vitamins and glucose grew equally as well as those in whole rat serum. Somite numbers attained did not change with increasing glucose concentration but a modest increase in micromoles of glucose used per embryo was found, suggesting the presence of another source of energy at lower glucose concentrations. The average glucose utilization per gram of protein per hour was 844 mumol in these day 9.5-10 embryos and this compares to 733 mumol previously found using uniformly labeled 14C glucose on day 10.3. Lactate production averaged 85% of the glucose utilized. Pyruvate did not support growth in the absence of glucose.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- T H Shepard
- Department of Pediatrics, University of Washington, Seattle 98195, USA
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Lange K, Brandt U. Rapid uptake of calcium, ATP, and inositol 1,4,5-trisphosphate via cation and anion channels into surface-derived vesicles from HIT cells containing the inositol 1,4,5-trisphosphate-sensitive calcium store. FEBS Lett 1993; 325:205-9. [PMID: 7686509 DOI: 10.1016/0014-5793(93)81074-a] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
In a previous study [K. Lange and U. Brandt (1993) FEBS Lett. 320, 183-188], we showed that the bulk of the ATP-dependent IP3-sensitive Ca2+ store of the hamster insulinoma cell line, HIT-T15, resides in cell surface-derived vesicles most likely of microvillar origin. The origin and orientation of these vesicles suggested that Ca2+ storage is not due to a membrane-located Ca2+ pumping ATPase but rather to ATP-dependent Ca(2+)-binding within the vesicles. In this case, Ca2+, ATP and IP3 should have free access to the vesicle lumen. This hypothesis was tested. ATP-independent Ca2+ uptake occurred with biphasic kinetics. An initial rapid uptake, which was complete within 30 s, was followed by a slow linear uptake lasting about 10 min. The rapid component was shown by efflux experiments to have an equilibration half-time of about 4 s. This rapid Ca2+ efflux pathway was inhibited by externally applied La3+ (0.1 mM). A similar rapidly equilibrating La(3+)-sensitive Ca2+ pool was also present in vesicles which had been actively loaded with Ca2+ in the presence of ATP. The intravesicular distribution space of this labile Ca2+ pool was identical with that of the non-metabolizable hexose analogue 3-O-methyl-D-glucose, demonstrating that rapid Ca2+ uptake occurs into a true vesicular water space and is not due to binding. ATP and IP3 were also shown to enter the vesicles by an energy-independent pathway which is inhibited by the anion channel inhibitor, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS; 0.5 mM). Both ATP-dependent Ca2+ uptake and IP3-induced Ca2+ release from preloaded vesicles were inhibited by DIDS. These findings clearly demonstrate that (1) the vesicle membrane is permeable to ATP and IP3 via anion channels, and (2) Ca2+ uptake into as well as IP3-induced Ca2+ release from the vesicles occur by passive diffusion through a cation channel which is not regulated by IP3. Consequently, the mechanisms for Ca2+ storage and IP3-induced Ca2+ release must be located in the vesicle lumen. Moreover, the microvillar diffusion-barrier concept, originally proposed for the regulation of hexose transport may also be valid for the receptor-operated regulation of cation and anion influx pathways.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- K Lange
- Institut für Pharmakologie, Freie Universität Berlin, Germany
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Shepard TH, Park HW, Pascoe-Mason J. Glucose causes lengthening of the microvilli of the neural plate of the rat embryo and produces a helical pattern on their surface. TERATOLOGY 1993; 48:65-74. [PMID: 8351650 DOI: 10.1002/tera.1420480111] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Prominent microvilli have been observed on the surface of neural plates in the embryos of many species. Since glucose is the main source of energy for embryos before neural tube closure and the onset of vascular circulation, it was of interest to study the relationship between these microvilli and glucose utilization in the neural plate. By applying microdrops of amniotic fluid to chemstrips, which colorimetrically measure glucose by glucose oxidase reaction, we determined that day 10 rat amniotic fluid glucose level was 31.6 +/- 1.6 mg/dl. On day 10 and within about 20 min from removal of the decidual sites, no glucose was found in the amniotic fluid. By use of a scanning electron microscope, the microvilli of the day 10 neural plate were found to have a 10-fold increase in length during a 40-min exposure to Hanks' solution at 21-23 degrees C. Similarly exposed embryos in Hanks' without glucose did not have microvillus elongation. However, under whole embryo culture conditions at 38 degrees C no extension of the microvilli was found. In the closed neural tube of the day 10 embryo, the microvilli were stubby and did not elongate with glucose exposure. Similarly, day 11 and 14 embryos had short microvilli which did not elongate with direct exposure to glucose at 21-23 degrees C. The short microvilli on the surface of the closed neural tube on day 11, 14, and 16 were associated with low glucose concentrations in the neural tube fluids. By use of a field emission scanning electron microscope, the surfaces of the microvilli in the extended position were seen to be covered by a right-handed helical array of globular objects the size of large molecules. The findings support the hypothesis that microvillar length may modulate glucose uptake. Shortening is associated with low concentrations of glucose in closed neural tubes, and lengthening occurs at glucose exposures of 100 mg/dl.
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Affiliation(s)
- T H Shepard
- Department of Pediatrics RD-20, University of Washington, Seattle 98195
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Lange K, Brandt U. The IP3-sensitive calcium store of HIT cells is located in a surface-derived vesicle fraction. FEBS Lett 1993; 320:183-8. [PMID: 8462684 DOI: 10.1016/0014-5793(93)80582-f] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Electron microscopic and biochemical techniques were used to study the cellular localization of the ATP-dependent, IP3-sensitive, Ca2+ store in the glucose- and phosphatidylinositol(PI) agonist-sensitive hamster insulinoma cell line HIT-T15. Scanning electron microscopy revealed conspicuous shape changes of the microvilli following stimulation of these cells with bombesin or thapsigargin. These changes closely resemble those previously shown to accompany stimulation of hexose transport in adipocytes with insulin [J. Cell. Physiol. 142 (1990) 1-14]. Using a hydrodynamic shearing technique for the isolation of microvilli, two cell surface-derived vesicle fractions were prepared containing 80% of the total cellular Ca(2+)-storing activity. In contrast, subcellular fractionation using normal homogenization with a glass/teflon homogenizer yielded the well-known distribution of the Ca(2+)-storing activity which is then predominantly recovered within the microsomal fraction. The surface-derived vesicle fraction was clearly distinguished from the microsomal fraction by its high content of Na+/K(+)-ATPase and an immunoreactive fragment of the GluT-1 glucose transporter isoform which both are not detectable in the microsomal fraction isolated from homogenates from sheared cells. The Ca2+ uptake properties of the cell surface-derived vesicle fractions including the vanadate, A23187, and thapsigargin sensitivity were found to be identical with those described for the microsomal Ca2+ stores of various cell types. Inositol 1,4,5-trisphosphate (IP3) at 1 microM induced a maximal release of 35-40% of the stored Ca2+ from these vesicles.
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Affiliation(s)
- K Lange
- Institut für Pharmakologie, Freie Universität Berlin, Germany
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Lange K, Brandt U. Restricted localization of the adipocyte/muscle glucose transporter species to a cell surface-derived vesicle fraction of 3T3-L1 adipocytes. Inhibited lateral mobility of integral plasma membrane proteins in newly inserted membrane areas of differentiated 3T3-L1 cells. FEBS Lett 1990; 276:39-41. [PMID: 2265708 DOI: 10.1016/0014-5793(90)80501-9] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The recent demonstration of a large cell surface-derived pool of insulin-sensitive glucose transporters, presumably concentrated in the microvilli of 3T3-L1 adipocytes, induced the assumption that in differentiated adipocytes, newly inserted plasma membrane areas may display restricted lateral mobility, thereby preventing diffusion of integral membrane proteins out of these areas into the adjoining plasma membrane. In order to test this assumption, the cell surface distributions of the two glucose transporter species expressed by 3T3-L1 cells were determined using specific antisera against the HepG2/erythrocyte transporter, GluT1, which is synthesized in both fibroblasts and adipocytes, and the adipocyte/muscle-specific transporter, GluT4, expressed for the first time 3-4 days after induction of adipose conversion. GluT1 was shown to be localized in the plasma membrane of both 3T3-L1 preadipocytes and adipocytes, whereas GluT4 was almost entirely restricted to the low density surface-derived vesicle (LDSV) fraction of 3T3-L1 adipocytes most likely consisting of microvilli-derived vesicles. In contrast to the minor portion of GluT4 found in the adipocyte plasma membrane fraction, equal amounts of the GluT1 protein were detected in both the plasma membrane and the LDSV fractions of adipocytes. Both transporter species were present in the microsomal and the LDSV fractions of adipocytes. The observed distribution of the two transporter species is in accordance with the postulated restriction of the lateral mobility in plasma membrane areas formed by newly inserted transgolgi vesicles of differentiated adipocytes.
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Affiliation(s)
- K Lange
- Institut für Pharmakologie, Freie Universität Berlin, FRG
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