We have characterized the effects of vinblastine on the growing and shortening dynamics at opposite ends of individual bovine brain microtubules at steady state in vitro by video microscopy. Vinblastine exerted strikingly different effects on the dynamics and polymer mass at the plus and minus ends of microtubules. At concentrations between 0.1 and 0.4 M, the drug strongly depolymerized microtubules at minus ends, whereas it did not significantly depolymerize microtubules at plus ends. Vinblastine stabilized plus ends by suppressing the rate and extent of growth and shortening, decreasing the catastrophe frequency, and increasing the rescue frequency. In contrast, vinblastine destabilized minus ends by increasing the catastrophe frequency and decreasing the rescue frequency, whereas it had no effect on the rate or extent of growth or shortening. Thus, vinblastine moderately increased the overall dynamicity at minus ends while strongly suppressing dynamicity at plus ends. Both the kinetic destabilization of microtubules at minus ends and the stabilization at plus ends may contribute to the altered function of mitotic spindle microtubules of cells blocked in mitosis by low concentrations of vinblastine.

Aim-Nanosized particles (NPs) enriched in hydroxyapatite and protein isolated from calcified human tissue accelerate occlusion of endothelium-denuded arteries when injected intravenously into rabbits. Since platelet aggregation and secretory processes participate in normal hemostasis, thrombosis and vascular remodeling, experiments were designed to determine if these biologic NPs alter specific platelet functions in vitro.Methods-Platelet-rich plasma was prepared from citrate anticoagulated human blood. Platelet aggregation and ATP secretion were monitored in response to thrombin receptor agonists peptide (10 μM) or convulxin (50 μg/ml) prior to and following 15 min incubation with either control solution, human-derived NPs, bovine-derived NPs or crystals of hydroxyapatite at concentrations of 50 and 150 nephelometric turbidity units.Results-Incubation of platelets for 15 min with either human-or bovine-derived NPs reduced aggregation induced by thrombin receptor activator peptide and convulxin in a concentrationdependent manner. Hydroxyapatite caused a greater inhibition than either of the biologically derived NPs. Human-derived NPs increased ATP secretion by unstimulated platelets during the 15 min incubation period.Conclusion-Effects of bovine-derived and hydroxyapatite NPs on basal release of ATP were both time and concentration dependent. These results suggest that biologic NPs modulate both platelet aggregation and secretion. Biologically derived NPs could modify platelet responses within the vasculature, thereby reducing blood coagulability and the vascular response to injury.

Self‐replicating, self‐calcifying nanosized particles (NPs) can be isolated from mammalian blood and calcified human tissue. Intravenous injection of these biologic NPs into rabbits accelerates occlusion of endothelium‐denuded carotid arteries. Since platelet activation is an initiating step in arterial repair, experiments were designed to determine if biologic NPs alter platelet functions. Platelet rich plasma was prepared from human citrate anti‐coagulated blood. Platelet aggregation (light transmission) and ATP secretion were monitored in response to sTRAP (10 μM) prior to and following incubation with either control solution, biologic NPs (50, 150, 500 NTUs) or hydroxyapatite (HA). NPs increased light transmission and ATP secretion when added immediately to the platelet solution. Both rate and maximal aggregation induced by sTRAP were reduced in the presence of NPs. NPs increased stimulated release of ATP at moderate doses but only after 15 minutes of incubation. HA crystals reduced rather than augmented ATP secretion. These results suggest that NPs cause a shape change in platelets and formation of microaggregates under basal conditions. NPs selectively augment agonist‐stimulated ATP secretion in a dose and time dependent fashion. Therefore, NP activation of platelets could contribute to the increased vascular response to injury in vivo.