Caffeine and nicotine: a review of their joint use and possible interactive effects in tobacco withdrawal

There is a strong, significant relationship between coffee consumption and smoking. In six epidemiological studies reviewed and analyzed here, 86.4% of smokers consumed coffee versus 77.2% of nonsmokers. Exsmokers use more coffee than nonsmokers but somewhat less than smokers. Seventeen experimental studies suggest that the pharmacologic effect of caffeine in coffee may be partially but not totally responsible for the relationship. Conditioning, a reciprocal interaction (caffeine intake increases anxiety/arousal--nicotine decreases it), or joint effect of a third variable (e.g., stress, alcohol) may account for the relationship. In abstinent smokers, blood caffeine levels increase and remain elevated for as long as 6 months. These higher caffeine plasma levels may be sufficient to produce caffeine toxicity syndrome. A review of 86 studies of nicotine withdrawal, caffeine withdrawal, and caffeine toxicity suggests that the symptoms are similar enough to be confused, and that reported nicotine withdrawal symptoms may be a mixture of nicotine withdrawal and caffeine toxicity.

Characterization of pulmonary endothelial charge barrier

To clarify the role of charge in protein movement across the pulmonary endothelial barrier, we simultaneously measured the permeability-surface area product (PS) for native [isoelectric point (pI) 4.4-5.1] and cationic (pI 7.2-8.0) albumin in isolated rabbit lungs perfused with and without protamine sulfate. We focused our measurement on the initial (endothelial) barrier by using a technique that is based on the very rapid (3 min) uptake of tracer. This allowed us to distinguish the charge properties of the endothelium separate from other barriers. In control studies, PS was greater for cationic than for native albumin (8.67 +/- 0.93 vs. 2.55 +/- 0.20 x 10(-2) ml.min-1.g dry lung-1). In the presence of 1 mg/ml protamine sulfate, cationic albumin permeability was not different from control (7.34 +/- 0.49 x 10(-2) ml.min-1.g dry lung-1), whereas PS for anionic albumin increased to 8.82 +/- 1.32 x 10(-2) ml.min-1.g dry lung-1. Thus the protamine sulfate eliminated the difference between native and cationic albumin PS. This selective increase in anionic albumin permeability is presumably due to the cation, protamine sulfate, binding to the anionic charges on the endothelium and reducing the anionic charge-charge repulsion. If protamine sulfate had produced a general endothelial injury, the PS for both albumins would have increased. Our results suggest that the normal pulmonary endothelium is an anionic charge barrier restricting the transcapillary movement of negatively charged molecules.

Salmonella stimulate macrophage macropinocytosis and persist within spacious phagosomes

Light microscopic studies of phagocytosis showed that Salmonella typhimurium entered mouse macrophages enclosed in spacious phagosomes (SP). Viewed by time-lapse video microscopy, bone marrow-derived macrophages exposed to S. typhimurium displayed generalized plasma membrane ruffling and macropinocytosis. Phagosomes containing Salmonella were morphologically indistinguishable from macropinosomes. SP formation was observed after several methods of bacterial opsonization, although bacteria opsonized with specific IgG appeared initially in small phagosomes that later enlarged. In contrast to macropinosomes induced by growth factors, which shrink completely within 15 min, SP persisted in the cytoplasm, enlarging often by fusion with macropinosomes or other SP. A Salmonella strain containing a constitutive mutation in the phoP virulence regulatory locus (PhoPc) induced significantly fewer SP. Similar to Yersinia enterocolitica, PhoPc bacteria entered macrophages in close-fitting phagosomes, consistent with that expected for conventional receptor-mediated phagocytosis. These results suggest that formation of SP contributes to Salmonella survival and virulence.

Effect of common vasodilators on lung microvascular permeability

The effect of papaverine on the albumin permeability-surface area product (PS), reflection coefficient (sigma), and capillary filtration coefficient (Kf) was examined in isolated rabbit lungs. Because PS and Kf are functions of vascular surface area and permeability, we also compared papaverine with two other means of maximizing lung surface area: isoproterenol (1 x 10(-7) M) and a mild increase in vascular pressure. Only lungs perfused with 0.1 mg/ml papaverine were significantly different from control. PS increased from control (2.80 +/- 0.16 to 5.53 +/- 0.20 ml.min-1.g dry lung-1 x 10(-2), whereas sigma decreased from control (0.92 +/- 0.01 to 0.78 +/- 0.03). Kf after papaverine was significantly lower than baseline predrug Kf (5.60 +/- 0.78 to 4.56 +/- 0.53 ml.s-1.cmH2O-1.g dry lung-1 x 10(-3). However, this group's predrug Kf was higher than that of any other group. Our results indicate that papaverine increases albumin permeability and decreases endothelial selectivity. The isolated perfused lung appears fully recruited, because Kf and PS did not increase with isoproterenol or increased vascular pressure. Papaverine should be used with caution in the Ringer-perfused lung.

Pure thoughts with impure proteins: permeabilized cell models of organelle motility

Permeabilized cell models provide an experimental middle ground wherein the in vitro properties of mechanochemical proteins can be reconciled with the physical and topological constraints of the intact cell. Several well-studied examples of organelle motility are described here, including the actin-based cytoplasmic streaming of Characean algae, the microtubule-based aggregation and dispersion of pigment granules in chromatophores and the saltatory movements of vesicles along microtubules in fibroblasts and macrophages. The permeabilized models developed for these systems have helped to integrate observations in vivo with in vitro assays of motor proteins.

HEPES buffer perfusate alters rabbit lung endothelial permeability

N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) has been shown to cause changes in cultured endothelial cells and smooth muscle function at concentrations from 5 to 25 mM. To determine whether HEPES also affects vascular permeability, the effects of two buffers, HEPES and phosphate, were compared in isolated perfused rabbit lungs. Hemodynamic parameters and vascular protein permeability-surface area products (PS) were measured after perfusion with the buffers. Endothelial permeability was measured for an anionic and a cationic albumin to assess the charge effects of the zwitterion buffer. With HEPES, there were no changes in vascular pressure or resistance but permeability was affected. Cationic albumin permeability increased with 12 mM HEPES (8.7phosphate-->30(12) mM HEPES x ml.min-1.g dry lung-1 x 10(-2)) as did the anionic albumin PS (2.7phosphate-->3.52(12) mM HEPES). The cationic PS returned to baseline (8.1(60) mM HEPES) at 60 mM HEPES, but the anionic PS did not change from the 12 mM HEPES (4.01(60) mM HEPES). In summary, we find that HEPES is not innocuous. Although hemodynamic parameters did not change, endothelial permeability was increased when HEPES was used at normal concentrations. Therefore, HEPES should be used with caution as a physiological buffer in perfused organ systems.

Macropinosome maturation and fusion with tubular lysosomes in macrophages

Macropinosomes formed by addition of recombinant macrophage colony-stimulating factor (rM-CSF) to mouse macrophages migrate centripetally and shrink, remaining detectable by phase microscopy for up to 15 min. This longevity allowed us to study how macropinosomes age. Macropinosomes were pulse labeled for 1 min with fixable fluorescein dextran (FDx10f), a probe for fluid phase pinocytosis, and chased for various times. To quantify changes in their antigenic profile, pulse-labeled macropinosomes of different ages were fixed and stained for immunofluorescence with a panel of antibodies specific for the transferrin receptor (TfR), the late endosome-specific, GTP-binding protein rab 7 or lysosomal glycoprotein A (lgp-A), and the percentage of antibody positive, FDx10f-labeled macropinosomes was scored. Some newly formed macropinosomes were positive for TfR, but few were rab 7 or lgp-A-positive. With intermediate chase times (2-4 min), staining for rab 7 and lgp-A increased to > 60%, while TfR staining declined. After a long chase (9-12 min), rab 7 staining returned to low levels while lgp-A staining remained at a high level. Thus, macropinosomes matured by progressive acquisition and loss of characteristic endocytic vesicle markers. However, unlike a maturation process, their merger with the tubular lysosomal compartment more nearly resembled the incorporation of a transient vesicle into a pre-existing, stable compartment. Shortly after their formation, FDx10f-labeled macropinosomes contacted and merged with Texas red dextran (TRDx10)-labeled tubular lysosomes. This occurred in two steps: macropinosomes acquired lgp-A first, and then several minutes later the cation-independent mannose-6-phosphate receptor (CI-MPR) and markers of lysosomal content (cathepsin L or pre-loaded TRDx10), all apparently derived from tubular lysosomes. Thus, macropinosome progress through macrophages showed features of both the maturation and vesicle shuttle models of endocytosis, beginning with a maturation process and ending by merger into a stable, resident lysosomal compartment.

Regulation of syrM and nodD3 in Rhizobium meliloti

The early steps of symbiotic nodule formation by Rhizobium on plants require coordinate expression of several nod gene operons, which is accomplished by the activating protein NodD. Three different NodD proteins are encoded by Sym plasmid genes in Rhizobium meliloti, the alfalfa symbiont. NodD1 and NodD2 activate nod operons when Rhizobium is exposed to host plant inducers. The third, NodD3, is an inducer-independent activator of nod operons. We previously observed that nodD3 carried on a multicopy plasmid required another closely linked gene, syrM, for constitutive nod operon expression. Here, we show that syrM activates expression of the nodD3 gene, and that nodD3 activates expression of syrM. The two genes constitute a self-amplifying positive regulatory circuit in both cultured Rhizobium and cells within the symbiotic nodule. We find little effect of plant inducers on the circuit or on expression of nodD3 carried on pSyma. This regulatory circuit may be important for regulation of nod genes within the developing nodule.

Salmonella typhimurium activates virulence gene transcription within acidified macrophage phagosomes

Survival of Salmonella typhimurium within macrophage phagosomes requires the coordinate expression of bacterial gene products. This report examines the contribution of phagosomal pH as a signal for expression of genes positively regulated by the S. typhimurium virulence regulators PhoP and PhoQ. Several hours after bacterial phagocytosis by murine bone marrow-derived macrophages, PhoP-activated gene transcription increased 50- to 77-fold. In contrast, no difference in PhoP-activated gene expression was observed after infection of cultured epithelial cells, suggesting that the membrane sensor PhoQ recognized signals unique to macrophage phagosomes. The increase in PhoP-regulated gene expression was abolished when macrophage culture medium contained NH4Cl or chloroquine, weak bases that raise the pH of acidic compartments. Measurements of pH documented that S. typhimurium delayed and attenuated acidification of its intracellular compartment. Phagosomes containing S. typhimurium required 4-5 hr to reach pH < 5.0. In contrast, within 1 hr vacuoles containing heat-killed bacteria were measured at pH < 4.5. The eventual acidification of phagosomes to pH < 5.0 correlated with the period of maximal PhoP-dependent gene expression. These observations implicate phagosome acidification as an intracellular inducer of PhoP-regulated gene expression and suggest that Salmonella survival is dependent on its ability to attenuate phagosome acidification.

Radial movement of lysosomes along microtubules in permeabilized macrophages

In murine bone marrow-derived macrophages, lysosomes often form tubulovesicular compartments, whose extended distribution in the cytoplasm depends on the integrity of cytoplasmic microtubules. When macrophages with fluorescently labeled lysosomes were plated onto coverslips opsonized with IgG, they engaged that surface in a phagocytic response (frustrated phagocytosis). The tubular lysosomal compartment of these cells collected in a central, perinuclear region, despite the continued presence of a radiating array of cytoplasmic microtubules. Using methods developed in the study of melanophores, we permeabilized macrophages engaged in frustrated phagocytosis, then re-activated lysosome extension along microtubules. Permeabilization was selective for plasma membranes, in that high molecular weight probes such as trypan blue or IgG could enter cells, while fluorescent probes previously loaded into lysosomes via endocytosis remained contained therein. Addition of 2 mM ATP, GTP or UTP to these permeabilized cell models produced centrifugal extension of tubular lysosomes. Selective depletion of ATP, using Escherichia coli glycerol kinase, inhibited ATP-dependent extension but not that which occurred with GTP or UTP, indicating that the mechanism of radial movement can use any of these three nucleotide triphosphates. Extension was independent of pH between 6.8 and 7.4, and was inhibited by AMP-PNP and by GMP-PNP. Depolymerization of cytoplasmic microtubules with nocodazole prevented subsequent ATP-inducible lysosome extension, whereas preincubation of cells with cytochalasin D did not inhibit the response. These results are consistent with the in vitro mechanochemical properties of kinesin (Cohn et al., 1989), and support earlier evidence, obtained in living cells, that kinesin is the mechanochemical motor of lysosome extension along microtubules in macrophages.

M-CSF-induced macropinocytosis increases solute endocytosis but not receptor-mediated endocytosis in mouse macrophages

Although coated vesicles can mediate both solute and receptor-mediated endocytosis, there are other kinds of endocytic vesicles that contribute to these processes. The relative contributions of these other organelles, particularly regarding solute influx, remains unsettled. Here we describe a physiological uncoupling of solute and receptor-mediated endocytosis that occurs during growth factor-stimulated macropinocytosis. We examined how recombinant human macrophage colony-stimulating factor (rM-CSF), which rapidly stimulates solute endocytosis in murine bone marrow-derived macrophages, affected ligand internalization via receptor-mediated endocytosis. Although rM-CSF stimulated internalization and accumulation of Lucifer Yellow (LY), a probe for solute endocytosis, it had no effect on accumulation of fluorescent acetylated low-density lipoprotein (acLDL), a ligand for the macrophage scavenger receptor, or on the endocytosis of 125I-labelled diferric transferrin. Video microscopy revealed that rM-CSF immediately induced active cell ruffling and the formation of phase-bright macropinosomes. Nocodazole pretreatment of macrophages inhibited both ruffling and macropinocytosis. Macropinosomes were fluorescently labelled by incubating macrophages briefly with probes for both solute endocytosis (fluorescent dextrans) and ligand endocytosis (fluorescein-labelled transferrin or diI-labelled acLDL). Macrophages incubated for one or two minutes formed macropinosomes that were labelled predominantly with the fluorescent solute probes but with little or none of the ligand probes; the latter were localized within smaller pinosomes. When cells pulsed with the fluorescent probes were washed and chased for an additional two minutes, solute and ligand probes occasionally co-localized in macropinosomes. Nocodazole inhibited macropinocytosis with little apparent effect on endocytosis via smaller vesicles. These experiments show that macropinosome formation is dependent on microtubules and also that the macropinosomes induced by rM-CSF are solute-rich and receptor-poor. Macropinosomes differ from coated vesicles in these respects, and therefore provide a physiologically regulated mechanism for uncoupling solute and receptor-mediated endocytosis.

Objectives to direct the training of emergency medicine residents on off-service rotations; radiologic imaging 1: Plain films

Interpretation of radiologic images is an essential skill for the emergency physician. This is the first of two sets of objectives for an off-service rotation in radiology. It covers the interpretation of plain films. The second series will address commonly used, but more sophisticated, imaging modalities including the use of contrast materials, ultrasound, nuclear medicine, computed tomography, and magnetic resonance imaging. This set of objectives may be used to guide a one-month radiology rotation or serve as part of a teaching program integrated with didactic training and emergency department experience.

The macrophage capacity for phagocytosis

Murine bone marrow-derived macrophages, which measure 13.8 +/− 2.3 microns diameter in suspension, can ingest IgG-opsonized latex beads greater than 20 microns diameter. A precise assay has allowed the determination of the phagocytic capacity, and of physiological parameters that limit that capacity. Ingestion of beads larger than 15 microns diameter required IgG-opsonization, and took 30 minutes to reach completion. Despite the dependence on Fc-receptors for phagocytosis of larger beads, cells reached their limit before all cell surface Fc-receptors were occupied. The maximal membrane surface area after frustrated phagocytosis of opsonized coverslips was similar to the membrane surface area required to engulf particles at the limiting diameter, indicating that the capacity was independent of particle shape. Vacuolation of the lysosomal compartment with sucrose, which expanded endocytic compartments, lowered the phagocytic capacity. This decrease was reversed when sucrose vacuoles were collapsed by incubation of cells with invertase. These experiments indicate that the phagocytic capacity is limited by the amount of available membrane, rather than by the availability of Fc-receptors. The capacity was also reduced by depolymerization of cytoplasmic microtubules with nocodazole. Nocodazole did not affect the area of maximal cell spreading during frustrated phagocytosis, but did alter the shape of the spread cells. Thus, microtubules may coordinate cytoplasm for engulfment of the largest particles.

Cellular dimensions affecting the nucleocytoplasmic volume ratio

Although it has long been appreciated that larger eukaryotic cells have larger nuclei, little is known about how this size relationship is maintained. Here we describe a method for measuring the aqueous volume ratio of nucleus to cytoplasm, two compartments which are interconnected via the pores in the nuclear envelope. We then use that method to identify proportional cellular dimensions in variously treated cells and in different cell types. Cells were scrape loaded with a mixture of fluorescent dextrans: Texas red dextran, average mol wt = 10,000 (TRDx10), and fluorescein isothiocyanate dextran, average mol wt = 70,000 (FDx70). After introduction into the cytoplasmic space, the TRDx10 distributed into both the nucleus and cytoplasm, whereas the FDx70 was restricted to cytoplasm, due to size exclusion by the nuclear pores. The aqueous nucleocytoplasmic volume ratio (RN/C) was determined by measuring, from fluorescence images of spread cells, total cellular fluorescence of each of the two probes and the fluorescence ratio of those probes in the cytoplasm. RN/C was unaffected by the measurement procedure or by varying temperatures between 23 degrees and 37 degrees C. Loading excess unlabeled dextrans had little effect on RN/C, with the single exception that high concentrations of large dextrans could lower RN/C in endothelial cells. Expanding intracellular membranous compartments of macrophages by phagocytosis of latex beads decreased RN/C. Expanding the same compartment by pinocytosis of sucrose, which nearly doubled total cell volume, had little effect on RN/C, indicating that nuclear volume was more closely linked to the cytoplasmic volume, exclusive of vesicular organelles, than to total cell volume. RN/C was the same in mononucleate and binucleate endothelial cells. Finally, measurements of RN/C in murine bone marrow-derived macrophages, bovine aortic endothelial cells, Swiss 3T3 fibroblasts, PtK2 cells, and CV-1 cells revealed that nuclear volume scaled allometrically with cell volume. The allometric relationship indicated that cell volume was proportional to nuclear surface area.

Head injury and the use of baby walkers: a continuing problem

STUDY OBJECTIVE

To determine the frequency of baby walker use as a contributing factor in head injuries in children less than 2 years old.

DESIGN

Retrospective clinical review.

SETTING

Urban Level I trauma center and multispecialty clinic.

TYPE OF PARTICIPANTS

All children less than 2 years old who were evaluated for a head injury during a three-year period.

MEASUREMENTS AND MAIN RESULTS

129 patients' cases were reviewed. Walker-related injuries occurred in 19 of 129 patients (14.7%). This represents the third most common mechanism of injury in this age group. Mean patient age at the time of injury was 8.7 months. Of the 19 accidents involving walkers, 18 (94.7%) involved falling down stairs. Nine children (47.4% of all walker-related injuries) suffered fractures of the cranial vault. No patients required surgical intervention, although one required treatment for post-traumatic meningitis.

CONCLUSION

Baby walkers continue to be a frequent cause of head injury in this age group, and further efforts must be made to deal with these preventable injuries.

Effect of interleukin-1 on gamete interaction and mouse embryo development

Early stages of endometriosis have been shown to be associated with infertility. The pathophysiology of this relationship is unclear. To determine if interleukin-1 (IL-1), a peritoneal macrophage product, has any effect on gamete interaction and early embryo development, human recombinant IL-1 was added to the coincubation of gametes in the sperm penetration assay (SPA), human zona pellucida assay (ZPPA) and culture medium (Ham's F-10) used for processing semen samples with the layering method, with analysis of velocity and motility after 24 hours. IL-1 was also added to mouse embryos (two cells) cultured for 72 hours. The results showed that IL-1 caused impairment of SPA and ZPPA when compared to control medium, without significant alterations in sperm velocity and motility. Also, IL-1 demonstrated significant inhibition of mouse embryo development. These results help explain subfertility associated with early stages of endometriosis.

Radial extension of macrophage tubular lysosomes supported by kinesin

The centrifugal elongation of membranes to form extended tubular structures is a widespread form of intracellular organelle movement. Tubular lysosomes and the endoplasmic reticulum, for example, undergo such extension in association with microtubules, and this process has been mimicked in vitro by combining purified microtubules with isolated membranes and the mechanochemical ATPase kinesin. This, along with evidence that kinesin is associated with the endoplasmic reticulum, has led to the suggestion that kinesin provides the motive force for the formation and maintenance of elongated tubulovesicular structures in cells. We have addressed this hypothesis in murine macrophages, which have prominent tubular lysosomes whose form depends on the integrity of microtubules. Here we report that two antikinesin antibodies which disrupt in vitro motility will each cause centripetal collapse of the array of tubular lysosomes when scrape-loaded into macrophages. To our knowledge this provides the first in vivo evidence that kinesin is responsible for extension of tubulovesicular structures along microtubules.

Plasticity of the tubular lysosomal compartment in macrophages

Because bone marrow-derived macrophages differentiate in culture, their lysosomal compartment is largely devoid of the undigested particles that are common in macrophages removed from tissues. The morphology of this nearly vacant lysosomal compartment was observed, after labeling with fluorescent endocytic tracers such as Lucifer Yellow, to be an extensive, tubuloreticular network, which underwent extensive rearrangements in accommodating endocytic loads. It was converted to spherical organelles when the lysosomal compartment was loaded with osmotically active solutes such as sucrose or Acridine Orange. Enzymatic degradation of intravacuolar sucrose by pinocytosed invertase resulted in the shrinkage of vacuoles and the re-formation of the tubular network. After phagocytosis of opsonized erythrocytes or latex beads, tubular lysosomes wrapped around the phagosomes, then merged to form phagolysosomes. The disappearance of tubules was proportional to the total surface area of particles ingested. Degradation of the phagocytosed contents permitted shrinkage of the phagolysosome and concomitant re-formation of the tubuloreticular network. Nondegradable contents such as latex beads prevented re-formation of the tubular network. These rearrangements of the lysosomal compartment indicate that the organelle exhibits considerable plasticity and interconnectedness, and that maturation of lysosomes after endocytosis does not necessarily entail irreversible morphological changes.

Macrophage colony-stimulating factor (rM-CSF) stimulates pinocytosis in bone marrow-derived macrophages

Incubation of murine bone marrow-derived macrophages (BMM) in medium containing recombinant macrophage colony-stimulating factor (rM-CSF) stimulated influx, efflux, and the net accumulation of the fluid-phase pinocytic marker, lucifer yellow (LY). Stimulation was dose dependent, occurred within 5 min of addition of the growth factor, and was sustained. Previous experiments had shown that BMM treated with PMA were stimulated to accumulate LY, but compared with rM-CSF-treated cells, the onset of stimulation in PMA-treated macrophages was slower. In further comparisons of rM-CSF- and PMA-stimulated LY accumulation, it was found that rM-CSF-stimulated pinocytosis could be abolished by pretreatment with 0.5 mg/ml trypsin, whereas neither unstimulated nor PMA-stimulated LY accumulation was affected by trypsin pretreatment. These findings indicate that the rM-CSF response was initiated at the cell surface, while the PMA response occurred via intracellular (or trypsin-resistant) receptors. However, once initiated, the pinocytic responses elicited by either agent were very similar. First, rM-CSF-treated cells, like PMA-treated cells, showed extensive ruffling and formation of large phase-bright pinosomes. Second, both rM-CSF- and PMA-stimulated LY accumulation could be inhibited by treatment of cells with the cytoskeleton destabilizing drugs nocodazole, colchicine, or cytochalasin D. Finally, rM-CSF, like PMA, was found to stimulate efflux of LY from cells preloaded with the dye. Thus, both rM-CSF and PMA stimulate the net rate of solute flow through the macrophage endocytic compartment.

Phorbol esters stimulate macropinocytosis and solute flow through macrophages

The morphology and kinetics of pinocytosis by bone marrow-derived macrophages were studied to determine how stimulation by phorbol esters increases net solute accumulation. Application of phorbol myristate acetate (PMA) increased both the abundance of macropinosomes and the rate of solute flow through the endocytic compartment. The large pinosomes originated as ruffles at the cell margins that folded back on themselves, internalizing extracellular medium and solutes. I examined how stimulation affects the kinetics of pinocytic influx, accumulation, and subsequent efflux of the fluorescent dye Lucifer Yellow (LY) in macrophages. Both the accumulation of LY and its subsequent efflux were temperature-dependent and directly proportional to the concentration of LY in the extracellular medium. Macrophages incubated in PMA and LY for 2 h accumulated four to six times more LY than did macrophages in LY alone. If after pinocytosis the macrophages were washed and reincubated in unlabeled medium for a 1 h chase period, some of the internalized LY was regurgitated from the cells. Inclusion of PMA in the chase medium increased efflux of LY. In contrast, a smaller percentage of LY was regurgitated from macrophages which were both loaded and chased in the presence of PMA. This indicates that although efflux is increased by PMA, influx increases more, and therefore more of the LY entering by pinocytosis is retained within the cell. I suggest that macropinocytosis increases the size difference between pinosomes and efflux vesicles, and that that difference increases greatly both solute accumulation and membrane flow through the endocytic compartment.

A prelysosomal compartment sequesters membrane-impermeant fluorescent dyes from the cytoplasmic matrix of J774 macrophages

After the membrane impermeant dye Lucifer Yellow is introduced into the cytoplasmic matrix of J774 cells, the dye is sequestered within cytoplasmic vacuoles and secreted into the extracellular medium. In the present work we studied the intracellular transport of Lucifer Yellow in J774 macrophages and the nature of the cytoplasmic vacuoles into which this dye is sequestered. When the lysosomal system of J774 cells was prelabeled with a Texas red ovalbumin conjugate and Lucifer Yellow was then loaded into the cytoplasm of the cells by ATP-mediated permeabilization of the plasma membrane, the vacuoles that sequestered Lucifer Yellow 30 min later were distinct from the Texas red-stained lysosomes. After an additional 30 min Lucifer Yellow and Texas red colocalized in the same membrane bound compartments, indicating that the Lucifer Yellow had been delivered to lysosomes. We next prelabeled the plasma membrane of J774 cells with anti-macrophage antibody and Texas red protein A before Lucifer Yellow was loaded into the cells. The phase-lucent vacuoles that subsequently sequestered Lucifer Yellow also stained with Texas red, showing that they were part of the endocytic pathway. J774 cells were fractionated on percoll density gradients either 15 or 60 min after Lucifer Yellow was introduced into the cytoplasmic matrix of the cells. In cells fractionated after 15 min, Lucifer Yellow was contained within the fractions of light buoyant density that contain plasma membrane and endosomes; the dye later appeared in vesicles of higher density which contained lysosomes. Secretion of Lucifer Yellow from the cytoplasmic matrix of J774 cells is inhibited by the organic anion transport blocker probenecid. We found that probenecid also reversibly inhibited sequestration of dye, indicating that sequestration of dye within cytoplasmic vacuoles was also mediated by organic anion transporters. These studies show that the vacuoles that sequester Lucifer Yellow from the cytoplasmic matrix of J774 cells possess the attributes of endosomes. Thus, in addition to their role in sorting of membrane bound and soluble substances, macrophage endosomes may play a role in the accumulation and transport of molecules resident in the soluble cytoplasm.

Fura-2 secretion and sequestration in macrophages. A blocker of organic anion transport reveals that these processes occur via a membrane transport system for organic anions

Fura-2, loaded into J774.2 macrophages as the acetoxymethyl ester, is sequestered into intracellular vacuoles within 90 min after the beginning of the loading at 37 degrees C. The dye is also efficiently secreted from the cells. Sequestration and secretion of fura-2 reduce the accuracy of measurements of cytosolic free Ca2+ concentration in this cell line. Fura-2 is also sequestered and secreted by J774.2 when the dye is loaded into the cytoplasm as the pentapotassium salt by reversible permeabilization of the plasma membrane. Regardless of the mechanism by which fura-2 is loaded into the cytoplasm, both sequestration and secretion are prevented by 2.5 mM probenecid, a blocker of organic anion transport. Probenecid has no effect on resting or stimulated cytosolic free Ca2+ levels or on FcR-mediated phagocytosis. These findings suggest that macrophages express a transport mechanism for the anionic form of fura-2. This transport system is responsible for the clearance of fura-2 from the cytoplasm of this cell type. Furthermore we suggest that use of probenecid to block secretion and intracellular sequestration of fura-2 may overcome problems arising in the application of this Ca2+ indicator to macrophages and perhaps to other cell types.

Fura-2 secretion and sequestration in macrophages. A blocker of organic anion transport reveals that these processes occur via a membrane transport system for organic anions

Fura-2, loaded into J774.2 macrophages as the acetoxymethyl ester, is sequestered into intracellular vacuoles within 90 min after the beginning of the loading at 37 degrees C. The dye is also efficiently secreted from the cells. Sequestration and secretion of fura-2 reduce the accuracy of measurements of cytosolic free Ca2+ concentration in this cell line. Fura-2 is also sequestered and secreted by J774.2 when the dye is loaded into the cytoplasm as the pentapotassium salt by reversible permeabilization of the plasma membrane. Regardless of the mechanism by which fura-2 is loaded into the cytoplasm, both sequestration and secretion are prevented by 2.5 mM probenecid, a blocker of organic anion transport. Probenecid has no effect on resting or stimulated cytosolic free Ca2+ levels or on FcR-mediated phagocytosis. These findings suggest that macrophages express a transport mechanism for the anionic form of fura-2. This transport system is responsible for the clearance of fura-2 from the cytoplasm of this cell type. Furthermore we suggest that use of probenecid to block secretion and intracellular sequestration of fura-2 may overcome problems arising in the application of this Ca2+ indicator to macrophages and perhaps to other cell types.