Biomedical subjects

S Greenberg

Publications and source records attributed to S Greenberg.

At least 91 records · Page 5Linked to original sources

PubMed1994

Selective pulmonary and venous smooth muscle relaxation by furosemide: a comparison with morphine.

Furosemide and morphine reduce pulmonary edema associated with congestive heart failure. It is uncertain whether furosemide or morphine are direct-acting relaxants of arterial and venous smooth muscle. The authors compared the effect of furosemide and morphine on isolated rings of canine pulmonary artery (PA) and vein (PV) and mesenteric, splenic and anterior tibial arteries and their corresponding veins precontracted with norepinephrine or (15S)-hydroxy-11 alpha, 9 alpha-(epoxymethano)prosta-5Z,13E-dienoic acid. Furosemide (10-300 microM) selectively relaxed veins by an endothelium-independent mechanism, with its greatest efficacy on the PV. Morphine (10-1000 microM) relaxed both arteries and veins. The mechanism of relaxation by furosemide and morphine was examined in the PV and PA. Morphine-induced relaxation of the PV and PA was dependent on prostanoid release from endothelium and smooth muscle because it was attenuated in endothelium-rubbed and ibuprofen-treated PV and PA but not in blood vessels treated with inhibitors of nitric oxide system/cyclic GMP system (I-NG-nitroarginine and methylene blue). Furosemide-mediated relaxation of the PV was refractory to each of these interventions. Similarly, furosemide- and morphine-induced relaxation of the PV were unaffected by 4-aminopyridine, tetraethylammonium, glibenclamide, dendrodotoxin and apamin and, thereby, were independent of an action on K+ channels. Reduction of extracellular K+ or Cl- attenuated furosemide-mediated relaxation of, and inhibition of 86Rb+ uptake by, PV even in the presence of ouabain. It was concluded that furosemide relaxes veins by an effect on Na+/K+/Cl- cotransport or chloride-mediated refilling of intracellular calcium stores.

Animals↗

PubMed1993

Alcohol administration attenuates LPS-induced expression of inducible nitric oxide synthase in Kupffer and hepatic endothelial cells.

This study investigates the effects of in vivo ethanol (primed infusion, causing 170-190 mg% plasma alcohol for 12 hours) and/or LPS (12 hours after injection of E. coli LPS 1 mg/kg bw.) on the mRNA expression of inducible nitric oxide synthase (NOS II) in hepatic cells measured by competitive PCR technique, and on hepatic release of reactive nitrogen intermediates (RNI, NO2- + NO3-). Perfused livers from alcohol- or saline-infused animals did not release measurable amounts of RNI. Under these conditions small amounts of NOS II mRNA were expressed in Kupffer and endothelial cells, while it was not detectable in parenchymal cells. LPS treatment along with markedly elevating hepatic RNI release increased NOS II mRNA levels by 35- and 200-fold, in endothelial and Kupffer cells, respectively. LPS injection and alcohol infusion to the same animal decreased hepatic RNI release by about 70% and almost completely inhibited the LPS-induced, elevated NOS II mRNA in Kupffer or endothelial cells. No similar changes were observed in the parenchymal cells. These data suggest that the primary target of in vivo LPS in upregulating hepatic NO release are the nonparenchymal cells. Furthermore, alcohol inhibits the LPS-induced response which may influence immune-related hepatic function.

Amino Acid Oxidoreductases↗

PubMed1993

Trimethoprim-sulfamethoxazole induces reversible hyperkalemia.

OBJECTIVE: To determine the effect of trimethoprimsulfamethoxazole (Tmp-Smx) on serum potassium concentration. DESIGN: Retrospective cohort study. SETTING: An urban teaching hospital. PATIENTS: Fifty-one persons hospitalized for symptomatic infection with human immunodeficiency virus (HIV). Twenty-five patients who were taking high-dose Tmp-Smx (trimethoprim 20 mg/kg per day; sulfamethoxazole, 100 mg/kg per day) for Pneumocystis carinii pneumonia were the study group. Twenty-six patients who had not received the drug were the control group. Patients who received potassium supplements, those taking medications known to alter potassium homeostasis or renal function, or those with a serum creatinine level more than 186 mumol/L were excluded. MEASUREMENTS AND MAIN RESULTS: Serum potassium concentration in the study group was 4.1 +/- 0.1 mmol/L (mean +/- SE) and increased by 1.1 mmol/L (Cl, 0.8 to 1.5 mmol/L) (P < 0.0001) 9.8 +/- 0.5 days after starting Tmp-Smx therapy. Patients followed longitudinally showed a progressive increase in serum potassium levels during therapy and a progressive decline after discontinuing Tmp-Smx. Blood urea nitrogen and serum creatinine levels increased mildly from 4.3 +/- 0.5 mmol/L and 85 +/- 6 mumol/L to 6.4 +/- 0.7 mmol/L and 113 +/- 8 mumol/L, respectively. The serum potassium level in the control group was 4.3 +/- 0.1 mmol/L and remained unchanged during hospitalization. CONCLUSIONS: High-dose Tmp-Smx therapy used for the treatment of P. carinii pneumonia in HIV-infected patients leads to an increase in the serum potassium concentration and may result in life-threatening hyperkalemia. Patients receiving high doses of Tmp-Smx require close monitoring of their serum potassium concentration, particularly 7 to 10 days after the start of therapy.

AIDS-Related Opportunistic Infections↗

PubMed1993

Tyrosine phosphorylation is required for Fc receptor-mediated phagocytosis in mouse macrophages.

Although Fc receptor-mediated phagocytosis is accompanied by a variety of transmembrane signaling events, not all signaling events are required for particle ingestion. For example, Fc receptor-mediated phagocytosis in mouse inflammatory macrophages (Di Virgilio, F., B. C. Meyer, S. Greenberg, and S. C. Silverstein. 1988. J. Cell Biol. 106:657; Greenberg, S., J. El Khoury, F. Di Virgilio, and S. C. Silverstein. 1991. J. Cell Biol. 113:757) and neutrophils (Della Bianca, V., M. Grzeskowiak, and F. Rossi. 1990. J. Immunol. 144:1411) occurs in the absence of cytosolic calcium transients. We sought to identify transmembrane signaling events that are essential for phagocytosis. Here we show that tyrosine phosphorylation is an early event after Fc receptor ligation in mouse inflammatory macrophages, and that the formation of tyrosine phosphoproteins coincides temporally with the appearance of F-actin beneath phagocytic cups. The distribution of tyrosine phosphoproteins that accumulated beneath phagocytic cups was punctate and corresponded to areas of high ligand density on the surface of the antibody-coated red blood cells, which provided the phagocytic stimulus. A tyrosine kinase inhibitor, genistein, but not several inhibitors of protein kinase C, blocked the appearance of tyrosine phosphoproteins as assessed by immunofluorescence, the focal accumulation of F-actin beneath immunoglobulin G-opsonized particles, and the ingestion of these particles as well. We suggest that tyrosine phosphorylation is a critical signaling event that underlies Fc receptor-mediated phagocytosis in mouse macrophages, and is necessary for the engulfment per se.

Actins↗

PubMed1993

Hyperkalemia with high-dose trimethoprim-sulfamethoxazole therapy.

In a patient with the acquired immunodeficiency syndrome, a progressive increase in the serum potassium concentration occurred with high-dose trimethoprim-sulfamethoxazole (TMP-SMX) therapy for Pneumocystis carinii pneumonia. In this patient, factors known to alter transcellular potassium shifts to induce hyperkalemia were not present. There was no evidence of glucocorticoid or mineralocorticoid insufficiency at the time of hyperkalemia, while the transtubular potassium gradient decreased. The hyperkalemia resolved spontaneously on discontinuation of TMP-SMX therapy, suggesting that this electrolyte abnormality is related to altered renal tubular secretion of potassium as a consequence of the high-dose TMP-SMX therapy.

AIDS-Related Opportunistic Infections↗

PubMed1993

Tumor necrosis factor-alpha inhibits endothelium-dependent relaxation.

Tumor necrosis factor-alpha (TNF-alpha) stimulates nitric oxide (NO) in vascular endothelium by induction of the enzyme NO synthase II (NOS II). We examined the effects of TNF-alpha on 1) endothelium-dependent (EDR) and endothelium-independent (EIR) relaxation and 2) contraction of bovine intralobar pulmonary arteries (BPA) and veins (BPV) in vitro. Acetylcholine (ACh), bradykinin (BK), histamine, and A23187 produced EDR of BPA contracted with a 50% effective concentration of U-46619 (15 nM), because relaxation was abolished by endothelium-rubbing and attenuated by L-NG-mono-methylarginine (L-NMMA; 300 microM). TNF-alpha (0.00417, 0.0417, 0.417, and 1.25 micrograms/ml) incubated with BPA for 60 min inhibited EDR of the BPA to ACh, BK, and histamine. The effects of TNF required 30 min for onset. Recovery of EDR occurred 3-4 h after washout of TNF-alpha. Pentoxifylline (1 microM) did not affect ACh-induced EDR but selectively reversed TNF-alpha-mediated inhibition of ACh-induced EDR. TNF-alpha-mediated inhibition of EDR was not reversible by L-NMMA, an inhibitor of NOS I and NOS II, the cyclooxygenase inhibitor ibuprofen, or CV-3908 (1 microM), a platelet-activating factor antagonist. The inhibitory effect of TNF-alpha on EDR was not mediated by nonspecific sensitization of the endothelium to human protein because recombinant human granulocyte colony-stimulating factor (10, 50, and 500 x 10(3) U/ml) did not affect EDR of BPA. The effect of TNF-alpha was specific for release of NO from the endothelium of BPA because TNF-alpha did not affect 1) EDR of BPV to ACh, BK, or ATP; 2) EIR of BPA or BPV to nitroprusside; and 3) contraction of either BPA or BPV to KCl, U-46619, histamine, norepinephrine, or serotonin. Thus TNF-alpha appears to selectively inhibit receptor-mediated EDR and NO release in BPA. TNF-alpha-mediated inhibition of EDR differs from that of L-arginine-based inhibitors and may represent an endogenous physiological mechanism of regulation of NO in the endothelium.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗

PubMed1992

Efficacy and risks of moricizine in inducible sustained ventricular tachycardia.

OBJECTIVE: To assess the efficacy and toxicity of moricizine in treating patients with serious ventricular arrhythmias and inducible sustained ventricular tachycardia. DESIGN: Uncontrolled clinical trial. SETTING: The intensive care and telemetry units of Northwestern Memorial Hospital, St. Francis Hospital and Medical Center, and Lenox Hill Hospital. PATIENTS: Twenty-six patients with sustained ventricular arrhythmias or hemodynamically significant nonsustained ventricular tachycardia, most of whom failed therapy with at least one class I antiarrhythmic agent. INTERVENTION: Patients were treated with moricizine, 400 to 1000 mg/d. MEASUREMENT: Efficacy was assessed by the results of programmed ventricular stimulation done during moricizine therapy. MAIN RESULTS: Seven of the 26 patients (27%) developed life-threatening ventricular proarrhythmia during moricizine loading. Three patients had incessant sustained ventricular tachycardia, two had incessant nonsustained ventricular tachycardia, one had new sustained ventricular tachycardia, and one had new cardiac arrest. One of these patients died of intractable ventricular fibrillation. No clinical or electrophysiologic variables clearly identified those at risk for proarrhythmia. Only 3 of 26 patients (12%) became noninducible on moricizine. CONCLUSION: Moricizine has a low rate of efficacy and carries a considerable risk for life-threatening proarrhythmia in patients with serious ventricular arrhythmias and inducible ventricular tachycardia who have failed therapy with other class I antiarrhythmic agents.

Adult↗

PubMed1992

Cardiomegaly on chest x-ray: prognostic implications from a ten-year cohort study of elderly subjects: a report from the Bronx Longitudinal Aging Study.

This report is from a 10-year cohort study of community-dwelling elderly men and women. Mean age at the time of entry into the study was 79 years. Annual chest x-ray studies were performed, and data are presented regarding prevalence, incidence, and prognosis of cardiomegaly. Cardiomegaly was defined as a transverse diameter of the cardiac silhouette greater than or equal to 50% of the transverse diameter of the chest (increased cardiothoracic ratio). At the time of entry into the study 110 subjects (23%) had cardiomegaly. After 10 years, 51% of the subjects with cardiomegaly at baseline died compared with 33% of the subjects without cardiomegaly (mortality rate = 9.1 vs 4.8/100 person-years respectively; p = 0.014). Cardiovascular disease incidence was also higher for those with preexisting cardiomegaly at baseline (rate 9.1 vs 6.1/100 person-years; p = 0.0001). According to the Cox proportional hazards regression analysis, age, cardiomegaly, diabetes, and prior evidence of myocardial infarction were independent predictors for death in this cohort. Similarly, the best predictive variables for cardiovascular disease were age, diabetes, prior evidence of myocardial infarction, and cigarette smoking. Of the 359 subjects without cardiomegaly at baseline, 108 (30%) showed evidence of new cardiomegaly, and their risk of cardiovascular disease was 1.8 times that of subjects whose test results were negative for cardiomegaly throughout the study (p = 0.003). Thus cardiomegaly, as defined by an increased cardiothoracic ratio on x-ray films, irrespective of cause, is associated with a poor prognosis in very elderly men and women.

Aged↗

PubMed1992

Strongyloides stercoralis hyperinfection in a carrier of HTLV-I virus with evidence of selective immunosuppression.

A patient with near fatal Strongyloides hyperinfection syndrome is briefly described. Investigation for possible risk factors for this parasitic infection disclosed that he was a carrier of human T-cell leukemia virus type I (HTLV-I), but without evidence of disease due to this retrovirus. Over the next few years, the patient's serum antibody levels of IgG to S. stercoralis larvae declined and became undetectable despite continued infection with the parasite. Repeated courses of appropriate treatment cleared the parasitic infection only temporarily. The patient was also found to have undetectable total serum IgE and a negative immediate hypersensitivity skin test to S. stercoralis antigens. Five of six other patients with HTLV-I-associated disease and with or without strongyloidiasis were also found to have very low total serum IgE levels. It is postulated that HTLV-I infection in certain individuals may selectively impair immune responses that are critical in controlling strongyloidiasis.

Antibodies, Helminth↗

PubMed1992

Environmentally contaminated families: therapeutic considerations.

The unique stress for families of exposure to environmental toxins is discussed in terms of the physical characteristics of such contaminants and resultant adaptational dilemmas, the agent or cause of the injury, and institutional responses to the contamination. Recommendations for mental health professionals working with contaminated families are presented.

Adaptation, Psychological↗

PubMed1992

Hypertension: cardiovascular implications in a cohort of old old.

OBJECTIVE: To examine the prevalence and cardiovascular implications of hypertension in advanced age. DESIGN: Prospective non-interventional study of a fixed cohort of very elderly subjects. PARTICIPANTS AND SETTING: The subjects were 488 community-dwelling volunteers. Mean age at entry was 79 years (range 75-85). All subjects were ambulatory, non-demented, and free of terminal illness at baseline. Participants were evaluated at the gerontology department of an urban medical school. MAIN OUTCOME MEASURES: Cardiovascular morbid and mortal events that were followed included fatal and non-fatal myocardial infarction, fatal and non-fatal stroke, and death. Prevalence of unrecognized myocardial infarction defined by electrocardiographic changes was also assessed. RESULTS: When hypertension was defined by history, current use of medications, or measured elevations in blood pressure, 78% of the subjects could be considered hypertensive. Univariate analysis showed an increased incidence of strokes in subjects with measured hypertension (P = 0.04). Subjects with elevated blood pressure (untreated) were more likely to develop clinically unrecognized myocardial infarction (P = 0.017). Multivariate survival analysis showed hypertension to be a modest predictor of overall cardiovascular disease (P = 0.067) but not of all-cause mortality. Left ventricular hypertrophy was a predictor of cardiovascular disease (P = 0.013) and all-cause mortality (P = 0.008). Age remained a significant risk factor for these endpoints, even in the very old. Isolated systolic hypertension was analyzed separately and in univariate analysis was a risk factor for stroke but not other cardiovascular morbidity. CONCLUSIONS: Hypertension at advanced age remains a modestly important risk factor in the development of cardiovascular disease.

Age Factors↗

PubMed1992

B-cell activation and differentiation by HIV-1 antigens among volunteers vaccinated with VaxSyn HIV-1.

The generation of memory B cells in response to vaccination with a baculovirus-derived recombinant gp160 candidate AIDS vaccine, VaxSyn HIV-1, was investigated in 12 healthy human volunteers who were immunized with VaxSyn HIV-1, hepatitis B vaccine, or alum adjuvant alone on days 1, 28, 180, and 540. Peripheral blood mononuclear cells were collected pre- and post-immunization and cultured unstimulated or with pokeweed mitogen (PWM), VaxSyn HIV-1 (rgp160), or HIV-1 lysate (iHIV-1) for 7 days before polyclonal and HIV-1-specific IgG production in culture supernatants (SNs) were measured. No differences were seen in the spontaneous or PWM-induced IgG production in SN from vaccinees and controls. Only vaccinee SN contained higher-than-normal levels of polyclonal IgG after stimulation with either rgp160 or iHIV-1, especially after the second and third booster immunizations on days 180 and 540, respectively. There were also contemporaneous increases in HIV-1-specific antibody in SN of all vaccinees, albeit at different time points throughout the study. We conclude that VaxSyn HIV-1 induces antigen-specific B-cell responses with the generation of memory B cells in vivo that can be reactivated in vitro to deliver an anamnestic response.

AIDS Vaccines↗

PubMed1991

Clinical and angiographic characteristics and outcome of patients with rest-unstable angina occurring during regular aspirin use.

Today many patients admitted with an acute coronary syndrome are already taking aspirin. Because they have symptoms despite antithrombotic therapy, these patients are presumed to be at higher risk for subsequent clinical events. In a pilot trial of antithrombotic therapy in patients with unstable angina at rest or non-Q wave infarction, 93 patients admitted within 48 h of pain were prospectively followed up for 12 weeks. On admission, 29 patients (31%) were already taking daily aspirin; 64 (68%) were receiving no antiplatelet agent. After enrollment all patients received antithrombotic therapy with either aspirin or heparin according to protocol regardless of prior aspirin use. The two groups (prior users versus nonusers of aspirin) were similar with regard to age, gender, coronary risk factors, prior antianginal medication, duration of symptomatic coronary disease, presentation with non-Q wave infarction and extent of electrocardiographic changes on admission. Quantitative analysis of coronary arteriograms (on a 0 to 10 scale) showed similar myocardium-in-jeopardy scores (JS). Follow-up events (recurrent ischemia [Isch], infarction [MI] and revascularization [Revasc]) were: (formula: see text) Aspirin users experiencing rest angina are similar to other patients with ischemic rest pain. The "resistant to aspirin" group does not constitute a subgroup that is at higher risk for cardiac events or revascularization.

Adult↗

PubMed1991

Usefulness of ST-segment changes in greater than or equal to 2 leads on the emergency room electrocardiogram in either unstable angina pectoris or non-Q-wave myocardial infarction in predicting outcome.

To determine the reliability of the admission electrocardiogram in predicting outcome in patients hospitalized for chest pain at rest, 90 patients were randomized into a trial of aspirin versus heparin in unstable angina or non-Q-wave myocardial infarction, and prospectively followed for 3 months. The emergency room admission electrocardiogram was analyzed for ST-segment deviation greater than or equal to 1 mm/lead and T-wave changes. Unfavorable outcomes were recurrent ischemic pain, myocardial infarction and coronary revascularization with angioplasty or surgery. In patients who underwent coronary arteriography, a myocardium in jeopardy score ranging from 0 to 10 was assigned, based on the number of vessels with a diameter stenosis greater than or equal to 70% and the location of the stenoses. Considering all 90 patients, an admission electrocardiogram with ST-segment deviation in greater than or equal to 2 leads had a positive predictive value for adverse clinical events of 79% and a negative predictive value of 64%. In the subset of patients without left ventricular hypertrophy and whose admission electrocardiograms were recorded during chest pain (62 of 90), the positive predictive value of ST deviation in greater than or equal to 2 leads improved to 89% and the negative value to 72%. Of the 62 patients, 53 underwent coronary arteriography. There was a positive linear correlation between the total number of leads with ST-segment deviation and the myocardium in jeopardy score (r = 0.80, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

PubMed1991

A fluorescence technique to distinguish attached from ingested erythrocytes and zymosan particles in phagocytosing macrophages.

While investigating the role of [Ca2+]i in Fc receptor-mediated phagocytosis, we found that clamping the [Ca2+]i to low levels by a variety of methods often led to increased plasma membrane permeability, rendering the hypotonic lysis method for calculating the phagocytosis index unreliable. To overcome this difficulty we developed a method for calculating the phagocytosis index of IgG-coated RBC that does not depend on hypotonic lysis. It depends on the ability of ingested RBC to create dark-appearing phagocytic vacuoles when the cytoplasm of murine macrophages is stained with acridine orange. Uningested or partially ingested RBC do not change the appearance of the otherwise uniformly stained cytoplasm of the macrophages. Since this method does not rely on hypotonic lysis to distinguish attached from ingested RBC, it can be used in situations when macrophages are unusually sensitive to hypotonic treatment (e.g. after clamping the macrophage [Ca2+]i to low levels). It can also be applied to the study of phagocytosis of particles that are not susceptible to hypotonic lysis (e.g., zymosan).

Acridine Orange↗

PubMed1991

Comparison of celiprolol and propranolol in stable angina pectoris. Celiprolol International Angina Study Group.

The comparative antianginal effects and safety of propranolol and celiprolol, a highly beta 1-selective adrenoceptor blocker with selective partial beta 2-adrenoceptor agonist activity, were assessed in an international multicenter, placebo run-in, active control, double-blind, randomized, titration-to-effect study of 140 patients with stable, exercise-induced angina pectoris. At baseline, all patients received placebo for 2 weeks, then titrated doses of once-daily celiprolol (200, 400, 600 mg) or twice-daily propranolol (total daily dose 80, 160, 320 mg) over 4 weeks, followed by a 2-week maintenance period. Heart rate and blood pressure, at rest and with exercise, weekly anginal attack frequency, nitroglycerin consumption and symptom-limited treadmill exercise times (modified Bruce protocol) were assessed. Compared with their respective baselines, both celiprolol and propranolol reduced anginal attack and nitroglycerin consumption rates to a comparable degree, while improving exercise tolerance (p less than 0.05). Treatment with propranolol compared with celiprolol, however, was associated with a significantly lower heart rate at rest (p less than 0.01). The double-product at the conclusion of exercise testing was significantly reduced by both drugs. Celiprolol and propranolol had similar effects on blood pressure, and were well tolerated. More symptomatic bradycardia occurred with propranolol. Despite the differences in their hemodynamic actions, once-daily celiprolol is as effective as twice-daily propranolol in the treatment of patients with stable angina pectoris.

Adrenergic beta-Antagonists↗

PubMed1991

Sustained ventricular tachycardia associated with sarcoidosis: assessment of the underlying cardiac anatomy and the prospective utility of programmed ventricular stimulation, drug therapy and an implantable antitachycardia device.

The presentation, cardiac anatomy and utility of programmed ventricular stimulation in seven patients with sustained ventricular tachycardia associated with sarcoidosis are described. The mean patient age was 38 +/- 8 years. Pulmonary involvement was apparent in three patients and no systemic manifestations of sarcoidosis were present in one patient. All patients had electrocardiographic abnormalities at rest and six had a left ventricular ejection fraction less than 45%. All seven patients had left ventricular wall motion abnormalities and five had mitral valve dysfunction. Sustained ventricular tachycardia was easily induced in all patients. Spontaneous sustained ventricular tachycardia was not prevented with corticosteroid administration. Despite antiarrhythmic drug therapy, two patients had sudden cardiac death and an additional four had recurrence of ventricular tachycardia. Four patients had an automatic cardioverter-defibrillator implanted and received drug therapy; all four received appropriate shocks. This report represents the largest descriptive series of consecutive patients with sustained ventricular tachycardia associated with sarcoidosis. Antiarrhythmic drug therapy of ventricular tachycardia in patients with sarcoidosis, even when guided with programmed ventricular stimulation, is associated with a high rate of arrhythmia recurrence or sudden death, or both. Thus, implantation of an automatic antitachycardia device (cardioverter-defibrillator) should be considered as primary therapy in such patients. Furthermore, sarcoidosis should be excluded, with Kveim skin testing if necessary, in any patient with sustained ventricular tachycardia of unknown origin.

Adult↗

PubMed1991

Ca(2+)-independent F-actin assembly and disassembly during Fc receptor-mediated phagocytosis in mouse macrophages.

Phagocytosis of IgG-coated particles by macrophages is presumed to involve the actin-based cytoskeleton since F-actin accumulates beneath forming phagosomes, and particle engulfment is blocked by cytochalasins, drugs that inhibit actin filament assembly. However, it is unknown whether Fc receptor ligation affects the rate or extent of F-actin assembly during phagocytosis of IgG-coated particles. To examine this question we have used a quantitative spectrofluorometric method to examine F-actin dynamics during a synchronous wave of phagocytosis of IgG-coated red blood cells by inflammatory mouse macrophages. We observed a biphasic rise in macrophage F-actin content during particle engulfment, with maxima at 1 and 5 min after the initiation of phagocytosis. F-actin declined to resting levels by 30 min, by which time particle engulfment was completed. These quantitative increases in macrophage F-actin were reflected in localized changes in F-actin distribution. Previous work showed that the number of IgG-coated particles engulfed by macrophages is unaffected by buffering extracellular calcium or by clamping cytosolic free calcium concentration ([Ca2+]i) to very low levels (Di Virgilio, F., B. C. Meyer, S. Greenberg, and S. C. Silverstein. 1988. J. Cell Biol. 106: 657-666). To determine whether clamping [Ca2+]i in macrophages affects the rate of particle engulfment, or the assembly or disassembly of F-actin during phagocytosis, we examined these parameters in macrophages whose [Ca2+]i had been clamped to approximately less than 3 nM with fura 2/AM and acetoxymethyl ester of EGTA. We found that the initial rate of phagocytosis, and the quantities of F-actin assembled and disassembled were similar in Ca(2+)-replete and Ca(2+)-depleted macrophages. We conclude that Fc receptor-mediated phagocytosis in mouse macrophages is accompanied by an ordered sequence of assembly and disassembly of F-actin that is insensitive to [Ca2+]i.

Actin Cytoskeleton↗