A variational calculus approach to the suspension flow problem using the minimal force hypothesis

Analytic expressions for the velocity profile and distribution of neutrally buoyant particles in laminar flow were obtained as functions of the radial distance. A modified Einstein viscosity model and the hypothesis that the total force on all the particles flowing in the tube is a minimum were used. The methods of the variational calculus were used in the mathematical development. A velocity profile differing only slightly from the parabolic form of that for Hagan-Poiseuille flow was obtained. For particle distribution the equations developed predict a maximum concentration along the center-line for some flows and a maximum concentration in a ring some distance from the center line in other flows. Both of these concentration profiles have been observed experimentally. Quantitative predictions from the equations derived must await further experimental work to permit calculation of the parameters included in the equations.     

Improved Plasmids for Fluorescent Protein Tagging of Microtubules in Saccharomyces cerevisiae

The ability to fluorescently label microtubules in live cells has enabled numerous studies of motile and mitotic processes. Such studies are particularly useful in budding yeast owing to the ease with which they can be genetically manipulated and imaged by live cell fluorescence microscopy. Because of problems associated with fusing genes encoding fluorescent proteins (FPs) to the native α‐tubulin (TUB1) gene, the FP‐Tub1 fusion is generally integrated into the genome such that the endogenous TUB1 locus is left intact. Although such modifications have no apparent consequences on cell viability, it is unknown if these genome‐integrated FP‐tubulin fusions negatively affect microtubule functions. Thus, a simple, economical and highly sensitive assay of microtubule function is required. Furthermore, the current plasmids available for generation of FP‐Tub1 fusions have not kept pace with the development of improved FPs. Here, we have developed a simple and sensitive assay of microtubule function that is sufficient to identify microtubule defects that were not apparent by fluorescence microscopy or cell growth assays. Using results obtained from this assay, we have engineered a new family of 30 FP‐Tub1 plasmids that use various improved FPs and numerous selectable markers that upon genome integration have no apparent defect on microtubule function.      

Biological evaluation of the bone healing process after application of two potentially osteogenic proteins: an animal experimental model

doi: 10.1111/j.1741‐2358.2011.00526.x
Biological evaluation of the bone healing process after application of two potentially osteogenic proteins: an animal experimental model Objective: The aim of this work was to analyse qualitatively and quantitatively the newly formed bone after insertion of rhBMP‐2 and protein extracted from Hevea brasiliensis (P‐1), associated or not with a carrier in critical bone defects created in Wistar rat calvarial bone, using histological and histomorphometrical analyses. Materials and methods: Eighty‐four male Wistar rats were used, divided into two groups, according to the period of time until the sacrifice (2 and 6 weeks). Each one of these groups was subdivided into six groups with seven animals each, according to the treatments: (1) 5 μg of pure rhBMP‐2, (2) 5 μg of rhBMP‐2/monoolein gel, (3) pure monoolein gel, (4) 5 μg of pure P‐1, (5) 5 μg of P‐1/monoolein gel and (6) critical bone defect controls. The animals were euthanised and the calvarial bone tissue removed for histological and histomorphometrical analyses. Result and conclusion: The results showed an improvement in the bone healing process using the rhBMP‐2 protein, associated or not with a material carrier in relation to the other groups, and this process demonstrated to be time dependent.     

The Effect of Surgical Weight Reduction on Left Ventricular Structure and Function in Severe Obesity

The aim of this study was to examine the effect of surgical weight reduction on cardiac structure and function and to seek the determinants of these changes. Sixty‐six severely obese adults (BMI ≥35 kg/m²) who received bariatric surgery underwent echocardiographic examination before and 3 months after surgery. At 3 months after surgery, BMI and systolic blood pressure (BP) decreased (43.3 ± 6.3 to 34.1 ± 5.6 kg/m², P < 0.001, and 146 ± 12 to 130 ± 14 mm Hg, P < 0.001, respectively). In left ventricular (LV) geometry, the relative wall thickness (RWT) and LV mass index decreased significantly (0.43 ± 0.05 to 0.35 ± 0.05, P < 0.001, and 50 ± 11 to 39 ± 11 g/m^2.7, P < 0.001, respectively) without changes in chamber size. Multivariate analyses showed change in systolic BP to be an independent predictor for the changes in RWT and LV mass index. In myocardial performance, peak systolic mitral annular velocity and all diastolic indexes showed significant improvements. We concluded that LV hypertrophy and function improved rapidly after bariatric surgery in severely obese adults. BP reduction was the major determinant for the regression of LV hypertrophy in the early stage of surgical weight reduction.     

Particle distribution for dilute suspension in flow

Analytic expressions for the velocity profile and particle distribution of a dilute suspension in flow were obtained as functions of radial distance. Einstein's linear viscosity model and the hypothesis of “minimum energy dissipation” were used. The methods of variational calculus were applied during the mathematical development. A parabolic velocity profile, which is a modified form of that for Hagen-Poiseuille flow, and a uniform particle distribution were obtained. An attempt is made to explain the results in light of some of the widely held theories on suspension flow and the rather severe limitations of Einstein's viscosity model. A suggestion for future work is made for improving the results of the present.     

Protein Phosphorylation at a Postreceptor Site Can Block Desensitization and Induce Potentiation of Secretion in Chromaffin Cells

Abstract: Desensitization or habituation to repeated or prolonged stimulation is a common property of secretory cells. Phosphorylation of receptors mediates some desensitization processes, but the relationship of phosphorylation to desensitization at postreceptor sites is not well understood. We have tested the effect of protein phosphorylation on desensitization in bovine chromaffin cells. To increase protein phosphorylation, we have used the protein phosphatase inhibitor okadaic acid at 12.5 nM, 100 pA4 8-bromo-cyclic AMP to activate protein kinase A, and 10 nM phorbol 12,13-dibutyrate to activate protein kinase C . During repeated 6-s stimulation at 5-min intervals, catecholamine secretion from control cells decreases. Cells exposed to 8-bromo-cyclic AMP or okadaic acid alone show slightly decreased rates of desensitization. In cells pretreated with phorbol 12,13-dibutyrate, desensitization is blocked. Okadaic acid-treated cells stimulated in the presence of 8-bromo-cyclic AMP show potentiation of secretion with repeated stimulation. The protein kinase inhibitor 1 -(5-iso-quinolinylsulfonyl)-2-methylpiperazine (H7) increases the desensitization rate. Because these phenomena are observed during secretion evoked with elevated Kf as well as by a nicotinic agonist, the effect of phosphorylation is at a postreceptor site. In contrast to desensitization to the repeated stimulations, desensitization to prolonged stimulation with high K+ is not altered by the above protocols in chromaffin Cells.     

Estrogen potentiates constrictor prostanoid function in female rat aorta by upregulation of cyclooxygenase-2 and thromboxane pathway expression

Estrogen potentiates vascular reactivity to vasopressin (VP) by enhancing constrictor prostanoid function. To determine the cellular and molecular mechanisms, the effects of estrogen on arachidonic acid metabolism and on the expression of constrictor prostanoid pathway enzymes and endoperoxide/thromboxane receptor (TP) were determined in the female rat aorta. The release of thromboxane A2 (TxA2) and prostacyclin (PGI2) was measured in male (M), intact-female (Int-F), ovariectomized-female (OvX-F), and OvX + 17beta-estradiol-replaced female (OvX + ER-F) rats. The expression of mRNA for cyclooxygenase (COX)-1, COX-2, thromboxane synthase (TxS), and TP by aortic endothelium (Endo) and vascular smooth muscle (VSM) of these four experimental groups was measured by RT-PCR. The expression of COX-1, COX-2, and TxS proteins by Endo and VSM was also estimated by immunohistochemistry (IHC). Basal release of TxA2 and PGI2 was similar in M (18.8 +/- 1.9 and 1,723 +/- 153 pg/mg ring wt/45 min, respectively) and Int-F (20.2 +/- 4.2 and 1,488 +/- 123 pg, respectively) rat aortas. VP stimulated the dose-dependent release of TxA2 and PGI2 from both male and female rat aorta. OvX markedly attenuated and ER therapy restored VP-stimulated release of TxA2 and PGI2 in female rats. No differences in COX-1 mRNA levels were detected in either Endo or VSM of the four experimental groups (P > 0.1). The expression of both COX-2 and TxS mRNA were significantly higher (P < 0.05) in both Endo and VSM of Int-F and OvX + ER-F, compared with M or OvX-F. Expression of TP mRNA was significantly higher in VSM of Int-F and OvX + ER-F compared with M or OvX-F. IHC revealed the uniform staining of COX-1 in VSM of the four experimental groups, whereas staining of COX-2 and TxS was greater in Endo and VSM of Int-F and OvX + ER-F than in OvX-F or M rats. These data reveal that estrogen enhances constrictor prostanoid function in female rat aorta by upregulating the expression of COX-2 and TxS in both Endo and VSM and by upregulating the expression of TP in VSM.