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PubMed1999

Lipopolysaccharide regulates macrophage fluid phase pinocytosis via CD14-dependent and CD14-independent pathways.

Lipopolysaccharide (LPS) is a mediator of inflammation and septic shock during bacterial infection. Although monocytes and macrophages are highly responsive to LPS, the biological effects of LPS in these cell types are only partially understood. We decided, therefore, to investigate the influence of LPS on macrophage pinocytosis and Fc receptor-mediated endocytosis, two prominent and related macrophage effector functions. We observed that LPS did not greatly influence endocytosis in either macrophages or monocytes, but did exert a dual action on pinocytosis: at lower concentrations (0.1 to 100 ng/mL), LPS caused a decrease in pinocytosis in both macrophages and monocytes, whereas at higher LPS concentrations, enhanced pinocytosis in macrophages was observed. Detoxified LPS was two orders of magnitude less potent in producing these effects. After inhibition of the LPS receptor CD14, the LPS-induced decrease in pinocytosis was absent, and stimulation of pinocytosis at lower LPS concentrations was unmasked. We conclude that LPS can influence pinocytosis via CD14-dependent and CD14-independent signaling pathways. Furthermore, as addition of LPS to macrophages effected pinocytosis but not Fc receptor-mediated endocytosis, these two processes are independently regulated in macrophages.

Animals↗
PubMed1982

Cold enhanced secretion of a pinocytosis-regulating factor in Amoeba proteus.

Low temperature inhibited preferentially pinocytosis induced by Na+ and Na+-like inducers, a category of inducers which are particularly dependent on the concentration of Ca++ that means susceptible to blockade by EGTA, La+++, or high Ca++. Coldness inhibited Na+-induced pinocytosis more effectively in cells from a calcium deficient medium than in normal cells and the inhibition was abolished by Ca++. In normally fed cells, a period of coldness prevented the subsequent induction of pinocytosis by Na+. This block was of the same type as that observed when the concentration of Ca++ was increased in the medium of normal cells kept at room temperature. In contrast, starved cells responded to coldness by an increased capacity for pinocytosis. These effects lasted for several hours after the cells had been rewarmed and were mediated by a cell-derived soluble factor, PRF, pinocytosis regulating factor. Solubility characteristics indicated that PRF is a lipid. Ca++, low pH, and low temperature stimulated accumulation of the factor in the medium. Preincubation with PRF or addition of PRF to the inducer stimulated pinocytosis in starved or Ca++-deficient cells and reduced the sensitivity to Na+-like inducers in normal cells. The amount of PRF secreted from cold cells was sufficient to cause the Ca++-like blockade of pinocytosis in the cold, the diminished pinocytotic activity after a cold period and the activating effect of coldness on starved cells. PRF appears to be an important physiological regulator of the capacity for pinocytosis in the amoeba.

Amoeba↗
PubMed1980

Enhanced rates of fluid pinocytosis during exponential growth and monolayer regeneration by cultured arterial endothelial cells.

Rates of fluid pinocytosis by bovine aortic endothelial cells were measured during various manipulations of growth status in vitro. Sparsely seeded cultures grew exponentially until a confluent monolayer was formed, at which time growth slowed. This change in growth rate coincided with a decline in the rate of pinocytosis to about one-third that in the growing cultures. During the subsequent attainment of maximal cell density in the confluent monolayer, the pinocytic rate remained constant. There was close correlation between 3H-thymidine labelling indices, as measured by autoradiography, and the rates of pinocytosis. Mechanical "wounding" of the confluent monolayer resulted in cell migration and proliferation. Twenty-four hours after "wounding," rates of pinocytosis per mg. cell protein were significantly enhanced. When regeneration of the monolayer was blocked by cytochalasin B, pinocytosis remained at the same rate as in the uninjured, confluent monolayer. These experiments support, and extend to endothelium, earlier observations that in growing cells pinocytosis proceeds at a higher rate than in non-growing, quiescent cells. Furthermore, they raise the possibility that the transendothelial transport of macromolecules such as lipoproteins by receptor-independent fluid pinocytosis in vivo may be altered by the growth status of the endothelium.

Animals↗
PubMed1990

Diacylglycerols and PMA are particularly effective stimulators of fluid pinocytosis in human neutrophils.

Diacylglycerols (OAG, diC8) and PMA were found to stimulate fluid pinocytosis (net uptake of FITC-dextran) to a far greater extent than other neutrophil activators, such as the chemotactic agents fNLPNTL and LTB4, the microtubule disassembling agents colchicine and nocodazole, the kinase inhibitor H-7, or D2O. OAG and diC8 produce a dose-dependent increase in the uptake of FITC-dextran, which is up to about 25- to 30-fold the control value of unstimulated neutrophils. The protein kinase inhibitor H-7 alone had a small stimulating effect on the net uptake, and it failed to inhibit stimulation of fluid pinocytosis by PMA, OAG, and diC8. Also, the protein kinase inhibitor staurosporine failed to inhibit fluid pinocytosis stimulated by OAG, diC8, and PMA. Stimulated fluid pinocytosis and vacuolization in response to PMA or diacylglycerols is associated with surface ruffling of neutrophils. Pinocytosis as well as surface ruffling stimulated by PMA, OAG, diC8, or diC10 are suppressed in the presence of cytochalasin D. The results suggest that diacylglycerols may be instrumental in transducing the signal for stimulated pinocytosis and that the surface movements induced by diacylglycerols, and PMA may be instrumental in fluid pinocytosis.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1994

Selective effects of the PKC inhibitors Ro 31-8220 and CGP 41,251 on PMN locomotion, cell polarity, and pinocytosis.

Using two newly synthesized inhibitors, Ro 31-8220 and CGP 41,251, of protein kinase C (PKC), we analysed: (1) how distinct PMN functions (shape changes, locomotion, pinocytosis) are regulated, and (2) the role of protein phosphorylation and PKC in this process. We were able to transform: (1) resting PMNs into locomoting cells using fNLPNTL, (2) locomoting cells into non-locomoting highly pinocytic cells using PMA, and (3) PMA-stimulated cells showing marked pinocytosis into locomoting or into resting cells using Ro 31-8220. It is thus possible to selectively manipulate PMN function (resting state, locomotion, marked pinocytosis), indicating that there are different regulatory pathways. It was not possible to induce locomotion and marked pinocytosis simultaneously, indicating crosstalk between pathways. Ro 31-8220 inhibited PMA-induced shape changes (nonpolar cells) and pinocytosis, but not fNLPNTL-induced shape changes (polarity) and pinocytosis. At higher concentrations, Ro 31-8220 alone elicited cell polarity and chemokinesis, indicating that a constitutively active protein kinase is involved in maintaining the spherical shape of resting PMNs. Functional effects of another PKC inhibitor, CGP 41,251, on neutrophil function were strikingly different. CGP 41,251 selectively inhibited fNLPNTL-induced polarity and locomotion (but not colchicine or Ro 31-8220-induced polarity), and it failed to inhibit PMA-induced, stimulated pinocytosis and shape changes. Although the effects of Ro 31-8220 vs. CGP 41,251 on PMN function were strikingly different, the inhibition of profiles for constitutive and for fNLPNTL- or PMA-induced protein phosphorylation in intact PMNs showed only small differences, which could not yet be conclusively related to cell function.

Alkaloids↗
PubMed1992

Regulation of pinocytosis in murine macrophages by colony-stimulating factors and other agents.

Lucifer yellow (LY) accumulation was used to measure macrophage pinocytosis. The hematopoietic growth factors, macrophage colony-stimulating factor (CSF-1), granulocyte-macrophage CSF (GM-CSF), and interleukin 3, and the macrophage activators, lipopolysaccharide and zymosan, all stimulated LY uptake in both murine bone marrow-derived macrophages (BMMs) and resident peritoneal macrophages (RPMs) without affecting LY efflux. The stimulation of pinocytosis in the poorly cycling RPMs and in BMMs by nonmitogens dissociates stimulation of pinocytosis from subsequent DNA synthesis. Regulation of pinocytosis in BMMs appears to be independent of that of urokinase-type plasminogen activator expression. The increases in CSF-mediated BMM pinocytosis were not inhibited by pertussis toxin, by elevations in intracellular cAMP, or by glucocorticoids and were only partially inhibited by inhibitors of Na+/H+ antiport and Na+/K(+)-ATPase activities. Protein kinase C activation could be involved in regulating BMM pinocytosis because phorbol myristate acetate, oleoylacyglycerol, and exogenously added phospholipase C can all stimulate it. Ca2+ ionophores were inactive, whereas the Na+/H+ ionophore monensin potently inhibited BMM pinocytosis.

Animals↗
PubMed1980

Cell-cell contact and growth regulation of pinocytosis in 3T3 cells.

In sub-confluent cultures of Balb/c-3T3 cells, pinocytosis rates were increased after exposure to specific growth factors (serum; platelet-derived growth factor, PDGF; epidermal growth factor, EGF). Conversely, as cells became growth-inhibited with increasing culture density, there was a corresponding decline in pinocytosis rate per cell. In order to test whether density-inhibition of pinocytosis was influenced either by the growth cycle or by cell contact independently of growth, cells were induced into a quiescent state at a range of subconfluent and confluent densities. Under such conditions, cell density did not significantly inhibit pinocytosis rate. When confluent quiescent cultures in 2.5% serum were exposed to 10% serum, the resulting round of DNA synthesis was accompanied by enhanced pinocytosis per cell, even though the cells were in contact with one another. Furthermore, in a SV40-viral transformed 3T3 cell line, both the growth fraction and the pinocytosis rate per cell remained unchanged over a wide range of culture densities. These studies indicate that density-dependent inhibition of pinocytosis in 3T3 cells appears to be secondary to growth-inhibition rather than to any direct physical effects of cell-cell contact.

Animals↗
PubMed1979

Naloxone-reversible effect of opioids on pinocytosis in Amoeba proteus.

A characteristic feature of induced pinocytosis in Amoeba proteus is the formation of broad channels by invagination of the cell membrane. This process, which requires Ca2+, occurs in response to depolarising cations. High Ca2+ levels reduce pinocytosis induced by cations such as Na+ and Tris+, whereas pinocytosis induced by K+ is less affected by Ca2+ (ref. 4). Agents which interfere with the calcium metabolism of the amoeba will therefore either stimulate or inhibit pinocytosis induced by Na+ (ref. 5). Among the agents which are supposed to reduce Ca2+ influx across cell membranes or otherwise decrease cellular availability of Ca2+ are the opiates and opioid peptides, high doses of which have been reported to affect the amoeba. Accordingly, Met-enkephalin, morphine and codeine potentiate the inhibition of pinocytosis caused by Ca2+-binding agents and reverse the calcium blockade of pinocytosis mediated by caffeine. In this report we show that pinocytosis induced by Na+ or Tris+ is suppressed by beta-endorphin, Metenkephalin and morphine. These effects were abolished or diminished by an opiate receptor antagonist, (-)naloxone, by increasing the Na+ concentration, or by addition of Ca2+.

Amoeba↗
PubMed1983

Dependence of fluid-phase pinocytosis in arterial smooth-muscle cells on temperature, cellular ATP concentration and the cytoskeletal system.

125I-labelled poly(vinylpyrrolidone) was used as a marker of fluid-phase pinocytosis in cultured pig arterial smooth-muscle cells. The rate of pinocytosis was temperature-dependent. A decrease in cellular ATP concentrations as a result of inhibition of either glycolysis or oxidative phosphorylation was associated with a similar decrease in pinocytosis. A microfibrillar-disruptive agent, cytochalasin B, caused a concentration-dependent stimulation of pinocytosis, whereas the microtubular-disruptive agents colchicine and vinblastine decreased pinocytosis to approximately half of control values at all concentrations used. These results indicate that fluid-phase pinocytosis in smooth-muscle cells is dependent on a continuing supply of energy and the integrity of the microtubules. Furthermore, microfilaments appear to exert a certain degree of constraint on pinocytosis, possibly by restricting invagination of the plasma membrane.

Adenosine Triphosphate↗
PubMed1980

Chloroquine inhibits lysosomal enzyme pinocytosis and enhances lysosomal enzyme secretion by impairing receptor recycling.

Adsorptive pinocytosis of acid hydrolases by fibroblasts depends on phosphomannosyl recognition markers on the enzymes and high-affinity pinocytosis receptors on the cell surface. In this study, beta-glucuronidase binding to the cell surface of attached fibroblasts was found to be saturable and inhibitable by mannose-6-phosphate (Man-6-P). Dissociation of cell-bound beta-glucuronidase occurred very slowly at neutral pH, but was greatly accelerated by lowering the pH below 6.0, or by exposure to Man-6-P. Comparison of the maximal cell surface binding and the observed rate of enzyme pinocytosis suggests that the pinocytosis receptors are replaced or reused about every 5 min. Enzyme pinocytosis was not affected by inhibition of new protein synthesis for several hours, suggesting a large pool of internal receptors and/or reuse of internalized receptors. Chloroquine treatment of normal human fibroblasts had three effects: (a) greatly enhanced secretion of newly synthesized acid hydrolases bearing the recognition marker for uptake, (b) depletion of enzyme-binding sites from the cell surface, and (c) inhibition of pinocytosis of exogenous enzyme. Only the third effect was seen in I-cell disease fibroblasts, which were also less sensitive than control cells to this effect. These observations are consistent with a model for transport of acid hydrolases that proposes that delivery of newly synthesized acid hydrolases to lysosomes requires the phosphomannosyl recognition marker on the enzymes, and intracellular receptors that segregate receptor-bound enzymes into vesicles for transport to lysosomes. This model explains how chloroquine, which raises intralysosomal pH, can disrupt both the intracellular pathway for newly synthesized acid hydrolases, and the one for uptake of exogenous enzyme by cell surface pinocytosis receptors.

Ammonium Chloride↗
PubMed1981

Inhibition of a nutrient-dependent pinocytosis in Dictyostelium discoideum by the amino acid analogue hadacidin.

In the present study we examine the effects of the drug hadacidin (N-formyl-N- hydroxyglycine) on pinocytosis in the eukaryotic microorganism dictyostelium discoideum. At concentrations of up to approximately 8 mg/ml, hadacidin inhibited the rate of pinocytosis of fluorescein isothiocyanate (FITC) dextran in cells in growth medium in a concentration-dependent manner but had no effect on cells in starvation medium. Because hadacidin also inhibits cellular proliferation at this concentration, the relationship between growth rate and pinocytosis was studied further using another drug, cerulenin, to produce growth-arrest. These experiments showed no changes in the rate pinocytosis even after complete cessation of cellular proliferation. Other studies showed that the transfer of cells from growth to starvation medium reduced the rate of pinocytosis by approximately 50 percent. A reduction of similar magnitude occurred if cells were transferred from growth to starvation medium containing hadacidin. Also, no additional reduction in pinocytosis occurred when cells that had been treated with hadacidin were transferred to starvation medium containing hadacidin. These cells were able to take up [(14)C]hadacidin in the starvation medium. In contrast to the results with hadacidin-treated cells, cells in a cerulenin-induced state of growth-arrest when transferred to starvation medium exhibited the same 50 percent reduction in pinocytosis observed in cells not previously exposed to either drug. Cells treated with azide, in either growth or starvation medium, exhibited an immediate inhibition of all pinocytotic activity. After the transfer of log-phase cells to starvation medium supplemented with glucose, the reduction in rate was only approximately 10-15 percent. In contrast, a 50 percent reduction was observed after supplementation of starvation medium with sucrose, KCl, or concanavalin A. Maintaining the cells in growth medium containing hadacidin for as long as 16 h had no effect on the rate at which cells aggregated. These results are consistent with the conclusion that D. discoideum exhibits two types of pinocytotic activity: one that is nutrient dependent and the other independent of nutrients. This latter activity persists in starvation medium and is unaffected by hadacidin, whereas the nutrient-dependent activity is present in growth medium and is inhibited by hadacidin.

Antibiotics, Antineoplastic↗
PubMed1989

The effects of acetylated low-density lipoproteins on fluid-phase pinocytosis by macrophages.

A simple method has been set up to measure the rate of fluid-phase pinocytosis in resident mouse peritoneal macrophages in culture. The method uses 125I-labelled polyvinylpyrrolidone as a nondegradable marker of fluid-phase pinocytosis. The accumulation of 125I-labelled polyvinylpyrrolidone by the cells was directly proportional to its concentration in the culture medium up to at least 200 micrograms/ml. The estimates of the rate of fluid-phase pinocytosis were reproducible within each experiment (coefficient of variation 8.5%) but varied between individual experiments. Fluid-phase pinocytosis was undetectable at 4 degrees C and reduced greatly at 37 degrees C by metabolic inhibitors and 1 mM ZnSO4. High concentrations of human acetylated low-density lipoproteins, which are taken up rapidly by macrophages, decreased the rate of fluid-phase pinocytosis by up to about 70%. The inhibition was seen after only 2 h of incubation. Unmodified low-density lipoproteins, which are taken up only slowly by macrophages, did not usually inhibit fluid-phase pinocytosis (in fact, they sometimes increased it). Modified low-density lipoprotein uptake, leading to massive lipid accumulation in macrophages in the arterial wall, has been postulated to be involved in the pathogenesis of atherosclerosis. This study raises the possibility that the rate of fluid-phase pinocytosis in these lipid-laden arterial macrophages may be reduced.

Acetylation↗
PubMed1976

Effect of ultraviolet radiation on pinocytosis in Amoeba proteua.

Ultraviolet (UV) irradiation (4 000-10 000 erg X mm(-2) decreased membrane potential and input resistance of Amoeba proteus and induced formation of pinocytotic channels. Submaximal pinocytosis induced by UV light was additive to pinocytosis induced by K+ or Na+ and stimulated in the presence of EGTA. It was not inhibited by the presence of La+++ or by pretreatment with dibucaine. In these respects and with respect to optimum pH and pCa, UV induced pinocytosis. Accumulation of K+ in the amoeba membrane after a dose of radiation may explain the similarity between pinocytosis induced by UV light and potassium salts. Ca++ present during the period of irradiation inhibited the effect of UV light. Instead Ca++ applied after irradiation (1-20 mM) increased channel formation. This effect was stimulated the presence of local anesthetic drugs. It is suggested that high doses of UV light may induce channel formation by releasing Ca++ from the cell membrane into the cell (UV induced pinocytosis). Ca++ may be released at the moment of absorption of UV light in the membrane as well as during the period of depolarization which follows irradiation. Low doses of UV light may permit extracellular Ca++ to enter the cell and stimulate channel formation (calcium induced pinocytosis). Dithiotreitol (1 mM) applied after irradiation depressed both UV and calcium induced pinocytosis so these may be the result of the same structural change which involves the formation of disulphide bonds in the membrane.

Amoeba↗
PubMed1988

Possible regulation of cation-induced pinocytosis in Amoeba proteus by phospholipase A.

We have studied the effects of exogenous phospholipids and compounds which are known to alter the activity of phospholipase A (PLA) on Ca2+-dependent, Na+-induced pinocytosis in Amoeba proteus. The PLA-inhibitors mepacrine, p-bromophenacyl bromide (pBPB) and Rosenthal's inhibitor depressed pinocytosis. Normal pinocytotic intensity was restored by the addition of Ca2+ or picomolar concentrations of lysolecithin. Very low concentrations of lysophospholipids and different molecular species of lecithins increased the capacity for pinocytosis in starved amoebae. The effect of the lecithins but not of the corresponding lysolecithins was abolished by PLA-inhibitors. Also, the restoration of the pinocytotic capacity of starved amoebae by melittin and mastoparan, which are known to stimulate PLA, was inhibited by mepacrine and pBPB. Isolated amoeba plasma membranes contain phospholipase A1 and A2 activity and the amoebae secrete a lipid (PRF, pinocytosis regulating factor) which has lysolecithin-like effects on pinocytosis. The enzyme activities and the release of PRF were markedly decreased by the PLA-inhibitors. Our observations support the hypothesis that PRF is a lysophospholipid that may constitute a signal for the formation of pinocytotic channels in the initial stages of pinocytosis. The phospholipase A activity of the amoeba must therefore be assigned an important role in the regulation of the Ca2+-dependent, cation-induced pinocytosis.

Amoeba↗
PubMed1990

Cell physiology of the rat visceral yolk sac: a study of pinocytosis and lysosome function.

The rat visceral yolk sac is active in pinocytosis. Macromolecules accumulated by the tissue are, in general, routed to the lysosomes, where they either accumulate (if non-digestible by the lysosomal enzymes) or are degraded to their monomeric components. The yolk sac cells engage in adsorptive pinocytosis, which leads to the preferential uptake of macromolecules bearing certain surface features, such as a hydrophobic or a cationic domain. Substrates that enter the yolk sac by adsorptive pinocytosis can in some cases act as bivalent ligands, carrying in a second substance by "piggy-back" pinocytosis. Pinocytosis and intralysosomal digestion of plasma proteins by the organogenesis-stage rat embryo play an important nutritional role, supplying a high proportion of the embryo's amino acid requirement. Teratogenic effects can be induced by substances that inhibit either pinocytosis or intralysosomal proteolysis at this sensitive stage of gestation.

Animals↗
PubMed1984

Activation of the capacity for sodium-induced pinocytosis in Amoeba proteus.

Amoebae treated with cycloheximide or starved for 8-10 days lose their pinocytotic response to Na+. Their capacity for Na+-induced pinocytosis was activated after application of various physical or chemical stimuli (electrical stimulation, mechanical shearing forces, osmotic pressure, UV-light, alkali metal ions, capsaicin, and indole). The degree of activation was related to the intensity and duration of the stimulus and lasted several hours after the stimulus had been withdrawn. The dose-response curves of activating stimuli were always biphasic. Strong activating agents reduced the sensitivity of the amoeba to the inducer. At concentrations lower than those which induced pinocytosis, but in the same order of efficacy, inorganic cations were potent activating agents. Like induction of pinocytosis, activation by cations required minute amounts of Ca2+ and was inhibited by high concentrations of this ion. Activation may therefore be an early event during the induction of pinocytosis. Capsaicin and indole were potent activators, indicating that specific chemical stimuli may increase the capacity for pinocytosis. The activation may be the result of a secretory process adding area and structures to the old membrane which are necessary for the induction of pinocytosis.

Action Potentials↗
PubMed1985

Phorbol esters and horseradish peroxidase stimulate pinocytosis and redirect the flow of pinocytosed fluid in macrophages.

Lucifer Yellow CH (LY) is an excellent probe for fluid-phase pinocytosis. It accumulates within the macrophage vacuolar system, is not degraded, and is not toxic at concentrations of 6.0 mg/ml. Its uptake is inhibited at 0 degree C. Thioglycollate-elicited mouse peritoneal macrophages were found to exhibit curvilinear uptake kinetics of LY. Upon addition of LY to the medium, there was a brief period of very rapid cellular accumulation of the dye (1,400 ng of LY/mg protein per h at 1 mg/ml LY). This rate of accumulation most closely approximates the rate of fluid influx by pinocytosis. Within 60 min, the rate of LY accumulation slowed to a steady-state rate of 250 ng/mg protein per h which then continued for up to 18 h. Pulse-chase experiments revealed that the reduced rate of accumulation under steady-state conditions was due to efflux of LY. Only 20% of LY taken into the cells was retained; the remainder was released back into the medium. Efflux has two components, rapid and slow; each can be characterized kinetically as a first-order reaction. The kinetics are similar to those described by Besterman et al. (Besterman, J. M., J. A. Airhart, R. C. Woodworth, and R. B. Low, 1981, J. Cell Biol. 91:716-727) who interpret fluid-phase pinocytosis as involving at least two compartments, one small, rapidly turning over compartment and another apparently larger one which fills and empties slowly. To search for processes that control intracellular fluid traffic, we studied pinocytosis after treatment of macrophages with horseradish peroxidase (HRP) or with the tumor promoter phorbol myristate acetate (PMA). HRP, often used as a marker for fluid-phase pinocytosis, was observed to stimulate the rate of LY accumulation in macrophages. PMA caused an immediate four- to sevenfold increase in the rate of LY accumulation. Both HRP and PMA increased LY accumulation by stimulating influx and reducing the percentage of internalized fluid that is rapidly recycled. A greater proportion of endocytosed fluid passes into the slowly emptying compartment (presumed lysosomes). These experiments demonstrate that because of the considerable efflux by cells, measurement of marker accumulation inaccurately estimates the rate of fluid pinocytosis. Moreover, pinocytic flow of water and solutes through cytoplasm is subject to regulation at points beyond the formation of pinosomes.

Animals↗
PubMed1978

Mediation of pinocytosis in cultured arterial smooth muscle and endothelial cells by platelet-derived growth factor.

Pinocytosis was measured in monkey aortic smooth muscle cells (SMC), bovine aortic endothelial cells, and Swiss 3T3 cells in culture as cellular uptake of [U-(14)C]sucrose and horseradish peroxidase (HRP) from the tissue culture medium. Monkey arterial SMC and Swiss 3T3 cells were maintained in a quiescent state of growth at low cells density in medium containing 5 percent monkey plasma-derived serum (PDS). Replacement of PDS with 5 percent monkey whole blood serum (WBS) from the same donor, or addition to PDS of partially purified platelet-derived growth factor(s) (PF), resulted in a marked stimulation of pinocytosis as well as of cellular proliferation. In SMC, enhancement of the rate of pinocytosis occurred 4-6 h after exposure to WBS or PF, and the rate was up to twofold higher than the rate in medium containing PDS. In contrast, [(3)H]thymidine uptake by SMC did not increase until 12-16 h after exposure to PF. In endothelial cells the presence of PF or WBS did not enhance either the rate of pinocytosis or the rate of proliferation over that in PDS. Thus, endothelial cells did not become quiescent at subconfluent densities in PDS but maintained rates of proliferation and pinocytosis that were equivalent to those in WBS. By autoradiography, the fraction of labeled nuclei in SMC cultures 24 h after change of medium increased from 0.061 +/- 0.004 in quiescent cultures to 0.313 +/- 0.028 after exposure to WBS or PF. In contrast, labeling indices of endothelial cells were similar for cultures grown in PDS, WBS, or PF at any single time point after change of medium. These findings suggest that the rate of pinocytosis maybe be coupled in some fashion to growth regulation, which may be mediated in part by specific growth factors, such as that derived from the thrombocyte.

Animals↗