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Biomedical subjects

K B Pastakia

Publications and source records attributed to K B Pastakia.

6 recordsLinked to original sources
PubMed1996

Adhesion of platelets to chemotactically responsive and non-responsive neutrophils.

Aims-To investigate the heterotypic adhesion of unactivated platelets to chemotactically responsive (migrated) and non-responsive (non-migrated) polymorphonuclear neutrophils (PMN).Methods-Platelets and PMN were isolated from autologous, normal blood. Migrated and non-migrated PMN were separated after N-formylmethionyl-leucylphenylalanine (FMLP) stimulation. Platelets were labelled with a fluorescent monoclonal antibody directed against CD41 (GPIIb-IIIa). Platelets (3 x 10(8)/ml) and PMN (3 x 10(6)/ml) were incubated together. Heterotypic cell adhesion was measured in isolated PMN and PMN co-incubated with platelets by flow cytometric analysis of platelet marker fluorescence in PMN gated events. Platelet-PMN adhesion was also visualised by fluorescence microscopy.Results-In studies of isolated PMN, contaminating platelets were bound to 16-34% of unstimulated PMN, 7-22% of stimulated PMN, 2-4% of migrated PMN, and 17-24% of non-migrated PMN. When platelets were co-incubated with migrated or non-migrated PMN, 15-78% of PMN bound one or two platelets.Conclusions-Unactivated platelets adhere to isolated PMN in vitro. Fewer unactivated platelets were adhered to migrated PMN than to non-migrated PMN in isolated PMN preparations. These results indicate that platelets adhering to PMN are removed during PMN migration.

Journal Article↗
PubMed1996

Amphotericin B induced abnormalities in human platelets.

Aims-To investigate in vitro the effect of amphotericin B on platelets in order to understand poor platelet recovery in patients receiving platelet transfusions and amphotericin B simultaneously.Methods-Washed platelets were isolated from platelet concentrates and exposed to amphotericin B (4 mug/ml) for one hour. Platelet function was assessed by aggregation response to thrombin (0-0.6 U/ml), serotonin release, response to hypotonic stress, and mean platelet volume. The expression of surface membrane glycoprotein (GP) Ib-IX complex, GPIIb-IIIa complex and CD62P (P-selectin) was examined by flow cytometry using fluorescence labelled monoclonal antibodies. Heterotypic cell adhesion was measured in amphotericin B treated platelets coincubated with isolated, autologous polymorphonuclear leucocytes (PMN) by flow cytometric analysis.Results-Amphotericin B induced platelet dysfunction. The rate of aggregation by thrombin, serotonin uptake and thrombin induced release of serotonin, and the response of platelets to hypotonic stress were inhibited. There was up to a two-fold increase in the mean platelet volume. The expression of platelet surface GPIb-IX and GPIIb-IIIa was not affected. P-selectin, normally expressed only on the surface of activated platelets, was also expressed on unactivated platelets. Amphotericin B increased platelet adherence to PMN and the number of platelets bound per PMN.Conclusions-In vitro, amphotericin B induces P-selectin expression on the surface of unactivated platelets and increases platelet adhesion to PMN, which is exacerbated by storage. Platelet dysfunction resulting from exposure to amphotericin B may contribute to poor platelet recovery in vivo when amphotericin B is administered concomitantly with platelet transfusion.

Journal Article↗
PubMed1993

Penicillin-induced dysfunction of platelet membrane glycoproteins.

We examined the effects of the beta-lactam antibiotic penicillin G on platelet function and on specific membrane glycoproteins in vitro. Platelet concentrates exposed to 3 to 10 mmol/L penicillin for 48 hours showed irreversible inhibition of aggregation by thrombin in washed platelets after removal of the antibiotic. Although a brief 15-minute exposure to similar doses of penicillin also inhibited thrombin aggregation, the inhibition was reversed on removal of the penicillin by washing. Aggregation activity was also restored to normal levels by stimulation with high thrombin concentrations (> 0.4 U/ml). Results of the aggregation studies led us to examine how penicillin affects platelet membrane proteins. Membranes isolated after 48 hours of exposure of platelet concentrates to penicillin showed no differences from the control in total protein profiles on sodium dodecylsulfate--polyacrylamide gel electrophoresis or in the glycoprotein Ib or IIb content on immunoblotting. However, flow cytometric analysis with fluorescently labeled monoclonal antibodies revealed that exposure of platelets to penicillin for 15 minutes inhibited thrombin-induced modulations in the glycoproteins Ib, Ib-IX, IIb-IIIa, and P-selectin. These effects were observed with washed platelets and platelets in plasma. Penicillin also inhibited the regulation of expression of glycoproteins Ib-IX and IIb-IIIa in adenosine diphosphate--activated platelets. The inhibitory effects were partially reversed at high agonist concentrations.

Adenosine Diphosphate↗
PubMed1992

Effect of albumin on the inhibition of platelet aggregation by beta-lactam antibiotics.

Platelet aggregation and bleeding time abnormalities are reported in patients receiving beta-lactam antibiotics (beta LAs), although clinical bleeding most frequently occurs in chronically ill, malnourished patients. Although most beta LAs bind to serum albumin, the relative influence of bound versus unbound beta LAs on platelet function is unknown. We examined the effect of beta LAs on the aggregation of gel-filtered platelets from normal subjects and on platelet-rich plasma (PRP) from hypoalbuminemic patients. Therapeutic concentrations of five beta LAs were added to normal platelets at different albumin concentrations (1.5 to 4.5 g/dL). Inhibition of aggregation by the beta LAs was inversely proportional to the albumin concentration, and most antibiotic-treated samples showed more than 50% inhibition at albumin levels below 2.0 g/dL. When PRPs from hypoalbuminemic patients were incubated with cephalothin, aggregation was completely inhibited, in contrast to samples from patients with normal albumin levels, and this decreased platelet aggregation was partially restored (25% to 75%) by increasing the albumin concentration above 4.0 g/dL. Specific binding of [35S]-benzylpenicillin to normal platelets decreased proportionately as the albumin concentration increased in the range of 1.0 to 5.0 g/dL. The inhibitory effects of beta LAs on platelets in vitro appear to be influenced by albumin concentration. Plasma albumin concentration may influence bleeding in patients receiving beta LAs.

Anti-Bacterial Agents↗
PubMed1987

Identification and characterization of a ribose transport system in Leishmania donovani promastigotes.

A transport system for ribose in Leishmania donovani promastigotes was identified and characterized by measuring the uptake of radioisotope-labeled ribose. The pentoses arabinose, 2-deoxyribose and xylose inhibited ribose uptake, whereas hexoses (glucose, alpha-methylglucoside, thioglucose, galactose, lactose, maltose, mannose), adenosine, and proline did not inhibit uptake, indicating that the transporter exhibited substrate specificity. Intracellular ribose exchanged with 2-deoxyribose. Uptake of ribose showed saturation kinetics with an apparent Km = 2 mM and Vmax = 11 nmol (mg protein)-1 min-1. Both N-ethylmaleimide and p-hydroxymercuribenzoate inhibited ribose uptake which was prevented by dithiothreitol. The uncoupling agents 2,4-dinitrophenol and carbonylcyanide p-(trifluoromethoxy)phenylhydrazone and a variety of inhibitors of energy-driven transport had no significant effect on ribose uptake. Following transport, the intracellular ribose pool contained two-thirds of the sugar in the phosphorylated form and one-third in the neutral form. These cumulative results indicate that a specific carrier mediates ribose uptake via a facilitated diffusion system in L. donovani promastigotes.

Animals↗