Phosphorylation of factor Va and factor VIIIa by activated platelets

Platelet activation leads to the incorporation of 32[PO4(2-)] into bovine coagulation factor Va and recombinant human factor VIII. In the presence of the soluble fraction from thrombin-activated platelets and (gamma-32P) adenosine triphosphate, radioactivity is incorporated exclusively into the M(r) = 94,000 heavy chain (H94) of factor Va and into the M(r) = 210,000 to 90,000 heavy chains as well into the M(r) = 80,000 light chain of factor VIII. Proteolysis of the purified phosphorylated M(r) = 94,000 factor Va heavy chain by activated protein C (APC) gave products of M(r) = 70,000, 24,000, and 20,000. Only the intermediate M(r) = 24,000 fragment contained radioactivity. Because the difference between the M(r) = 24,000 and M(r) = 20,000 fragments is located on the COOH-terminal end of the bovine heavy chain, phosphorylation of H94 must occur within the M(r) = 4,000 peptide derived from the carboxyl-terminal end of H94 (residues 663 through 713). Exposure of the radioactive factor VIII molecule to thrombin ultimately resulted in a nonradioactive light chain and an M(r) = 24,000 radioactive fragment that corresponds to the carboxyl-terminal segment of the A1 domain of factor VIII. Based on the known sequence of human factor VIII, phosphorylation of factor VIII by the platelet kinase probably occurs within the acidic regions 337 through 372 and 1649 through 1689 of the procofactor. These acidic regions are highly homologous to sequences known to be phosphorylated by casein kinase II. Results obtained using purified casein kinase II gave a maximum observed stoichiometry of 0.6 mol of 32[PO4(2-)]/mol of factor Va heavy chain and 0.35 mol of 32[PO4(2-)]/mol of factor VIII. Phosphoamino acid analysis of phosphorylated factor Va by casein kinase II or by the platelet kinase showed only the presence of phosphoserine while phosphoamino acid analysis of phosphorylated factor VIII by casein kinase II showed the presence of phosphothreonine as well as small amounts of phosphoserine. The platelet kinase responsible for the phosphorylation of the two cofactors was found to be inhibited by several synthetic protein kinase inhibitors. Finally, partially phosphorylated factor Va was found to be more sensitive to APC inactivation than its native counterpart. Our findings suggest that phosphorylation of factors Va and VIIIa by a platelet casein kinase II- like kinase may downregulate the activity of the two cofactors.     

A survey of knowledge, attitudes, and beliefs of house staff physicians from various specialties concerning antimicrobial use and resistance

BACKGROUND: Examination of knowledge, attitudes, and beliefs of house staff physicians will be important in developing interventions to improve antimicrobial use and prevent resistance. METHODS: A 75-item survey was distributed to house staff physicians on nonpediatric services in a university teaching hospital. Knowledge was assessed with a 10-question quiz. RESULTS: The survey was completed by 179 (67%) of 269 house staff physicians on 5 specialties. Outside and inside the intensive care unit, 21% and 25% of respondents, respectively, reported that they were using antibiotics optimally. Surgeons were significantly more likely than other physicians to report that they were regularly seeking input into antimicrobial selections (P<.001). Of the 170 physicians who completed the survey, 88% agreed antibiotics are overused in general and 72% also agreed this was the case at their institution (r = 0.56; P<.05); 96% agreed that hospitals in general face serious problems with antibiotic resistance and 93% agreed that their hospital faces these same problems (r = 0.57; P<.05); 97% agreed that better use of antibiotics would reduce resistance; 32% stated that they had not had formal teaching on antimicrobial agents in the last year (medicine residents reported significantly more formal teaching than others [P =.001]); and 90% wanted more education about antimicrobials and 67% wanted more feedback on antimicrobial selections. The mean antimicrobial quiz score was 28%, with medicine residents scoring significantly higher than others (P =.04). Upper-level residents did not perform better than interns. CONCLUSIONS: This survey (1) revealed that house staff are aware of the importance of antimicrobial resistance and believe better antimicrobial use will help this problem and (2) demonstrated differences between specialties with respect to antimicrobial use and knowledge. House staff at our hospital have suboptimal knowledge about antimicrobials, and this knowledge did not increase appreciably over the course of their training. Antimicrobial education is needed and is likely to be well received by house staff physicians in academic centers but may be more effective if it is tailored to specific specialties.     

Decreased expression of phospholipase C-beta 2 isozyme in human platelets with impaired function

Platelets from a patient with a mild inherited bleeding disorder and abnormal platelet aggregation and secretion show reduced generation of inositol 1,4,5-trisphosphate, mobilization of intracellular Ca2+, and phosphorylation of pleckstrin in response to several G protein mediated agonists, suggesting a possible defect at the level of phospholipase C (PLC) activation (see accompanying report). A procedure was developed that allows quantitation of platelet PLC isozymes. After fractionation of platelet extracts by high-performance liquid chromatography, 7 out of 10 known PLC isoforms were detected by immunoblot analysis. The amount of these isoforms in normal platelets decreased in the order PLC- gamma 2 > PLC-beta 2 > PLC-beta 3 > PLC-beta 1 > PLC-gamma 1 > PLC- delta 1 > PLC-beta 4. Compared with normal platelets, platelets from the patient contained approximately one-third the amount of PLC-beta 2, whereas PLC-beta 4 was increased threefold. These results suggest that the impaired platelet function in the patient in response to multiple G protein mediated agonists is attributable to a deficiency of PLC-beta 2. They document for the first time a specific PLC isozyme deficiency in human platelets and provide an unique opportunity to understand the role of different PLC isozymes in normal platelet function.     

Brief Report: Shared partisanship dramatically increases social tie formation in a Twitter field experiment

Americans are much more likely to be socially connected to copartisans, both in daily life and on social media. However, this observation does not necessarily mean that shared partisanship per se drives social tie formation, because partisanship is confounded with many other factors. Here, we test the causal effect of shared partisanship on the formation of social ties in a field experiment on Twitter. We created bot accounts that self-identified as people who favored the Democratic or Republican party and that varied in the strength of that identification. We then randomly assigned 842 Twitter users to be followed by one of our accounts. Users were roughly three times more likely to reciprocally follow-back bots whose partisanship matched their own, and this was true regardless of the bot’s strength of identification. Interestingly, there was no partisan asymmetry in this preferential follow-back behavior: Democrats and Republicans alike were much more likely to reciprocate follows from copartisans. These results demonstrate a strong causal effect of shared partisanship on the formation of social ties in an ecologically valid field setting and have important implications for political psychology, social media, and the politically polarized state of the American public.     

von Willebrand factor antigen is not an accurate marker of rat and guinea pig liver endothelial cells

To determine whether von Willebrand Factor (vWF) is a valid marker of liver endothelial cells, we determined vWF immunoreactivity in rat and guinea pig liver sections and in smears of elutriated nonparenchymal cells isolated from these two species. In frozen sections, positive staining for vWF was seen only in the endothelium lining large hepatic vessels in both species, and no immunoactivity was detected in the sinusoids. On the other hand, immunohistochemical staining for vimentin (a marker of mesenchymal cells) showed positive reaction throughout the vascular and sinusoidal endothelial cells in both the rat and guinea pig liver. In fractions of elutriated rat and guinea pig nonparenchymal liver cells, which included almost exclusively liver endothelial cells, only 25-40% of the cells displayed a positive reaction for vWF. However, when these same fractions were stained for vimentin, 70-95% of the cells exhibited immunoreactivity. Most of the vWF-negative cells were not red and white blood cells, biliary epithelial and Kupffer cells, and hepatocytes, and had ultrastructural features of sinusoidal endothelial cells. We conclude that in both the rat and guinea pig, liver sinusoidal endothelial cells do not exhibit vWF immunoreactivity. Thus, in routine immunohistochemical assays, vWF is not an accurate marker of rat and guinea pig liver endothelial cells. Vimentin is more appropriate for this purpose, provided that other mesenchymal cells are separated or independently identified.     

Possible effect of secretor locus on plasma concentration of factor VIII and von Willebrand factor

A significant fraction (30%) of the genetically determined variance in plasma concentration of the von Willebrand factor antigen (vWf:Ag) has been shown to be related to ABH determinants. Individuals with blood group O, who have the highest amounts of blood group H substance, have the lowest concentration of vWf:Ag. The Lewis substances, Le(a) and Le(b), are biochemically closely related to the ABH substances as both can be produced from the same precursor substance. We studied the effect of the presence of the Lewis antigens on the plasma concentration of vWf:Ag and factor VIII antigen (VIII:Ag) in 323 individuals of different ABO groups from a series of twins and in 58 blood donors of blood group O. Among persons belonging to blood group O, those with the Le(a) antigen had a higher concentration of both vWf:Ag and VIII:Ag than individuals lacking Le(a). Le(a+b-) people are nonsecretors and Le(a-b+) people are secretors of ABH substance. Thus, the lowest concentration of vWf:Ag and VIII:Ag was found in group O secretors. The effect is most likely due to an effect of the secretor locus. This finding may be of importance for the detection of carriers of hemophilia A and for the diagnosis of type I von Willebrand disease.     

An Extension and Moderational Analysis of the Family Stress Model Focusing on African American Adolescents

This study focuses on 422 African American families with two caregivers as children transition into adolescence. The family stress model was tested longitudinally using structural equation modeling. Results showed that economic stress was associated with economic pressure and depressive symptoms among caregivers, which in turn was related to caregiver conflict. Higher levels of conflict had a negative influence on parenting quality at Wave 2, and this was linked to adolescent functioning. The depressive symptomology of secondary caregivers (SCs) exerted a greater indirect effect in the models than that of primary caregivers (PCs) and had a direct relationship to adolescent's positive adjustment. Moderational effects of caregiver conflict on the link between economic pressure/adolescent outcomes and economic pressure/hostile parenting were also tested. The case for the importance of including PCs and SCs of children and adolescents in future research focusing on African American families facing economic hardship is made.     

Absence of mast cells in diabetic retinopathy

The vascular beds of femoral biceps, soleus, and medial gastrocnemius of the rat were perfused with India ink to outline the capillary network. Histologic cross sections were stained with picric acid and basic fuchsin. By this method, the muscle fiber nuclei appeared red and could be clearly distinguished from the darker-stained capillary profiles. A specific anatomic relationship between capillaries and muscle fiber nuclei was tested against a random orientation by an analysis of independence. Systematic sampling was performed by positioning the center of an eyepiece reference circle on the uppermost point of each fiber profile. The frequencies of the four combinations (fiber nuclei and/or capillaries or neither) found within each test circle were recorded and stored in 2 × 2 contingency tables. The Z test of independence revealed a highly significant relationship between capillaries and fiber nuclei in all muscles examined. The nonrandom nucleus-related location of capillaries around muscle fibers was even more evident after pooling the individual muscle data in a single table (P ? 0.00001). These findings suggested a chemotactic attraction of capillaries by the muscle fiber nuclei. This observation is supported by the high concentration of cytoplasmic organelles present in nuclear regions of skeletal muscle fibers, that is well documented in the literature. These organelles may be responsible for the production and local secretion of chemotactic factors “to attract” capillaries, and hence provide for their characteristic orientation and distribution in muscle.     

Daily stress and recurrence of genital herpes simplex

It is widely believed that emotional stress triggers recurrences of both oral and genital herpes simplex virus. On a daily basis, we studied 64 subjects prospectively for 1 to 3 months; all subjects had at least one culture-proved recurrence of genital herpes simplex virus type 2 before or during the study. All subjects filled out a questionnaire that measured psychological/emotional stress in six areas: physical health, relations with friends, relations with family, relations with sex partner(s), financial, and vocation/education. These questionnaires were mailed back to us daily. Data were analyzed by General Linear Models analysis of variance to compare stress reported on each of the 6 days before a recurrence with that on days during or after a recurrence, as well as days not temporally related to recurrence. Under these conditions, in which retrospective bias was minimized, there was no significant increase in psychological/emotional stress on any day in any area preceding a recurrence of genital herpes simplex virus.