Applicability of an allometric power equation to children, adolescents and young adults of extreme body size.

AIM: The aim of this study was to assess the applicability of a regression model for peak power (PP) and total mechanical work (TMW) for healthy children, adolescents and young adults especially in the extreme ranges of stature, mass, and body mass index (BMI). METHODS: A total of 454 children, adolescents and young adults aged 6-20 years volunteered for the study. Subjects, whose stature, mass and BMI were between the 10(th) and the 90(th) centile, were selected to calculate the prediction equation: 267 subjects fulfilled these criteria. Each subject performed two unilateral Wingate tests (ULWAnT), one with each leg. PP (Watts) and TMW (Joules) of the left and right leg were averaged for each individual. Ln(mass), in(stature), age, age(2), gender, and age x gender were used as predictors for in(PP) and ln(TMW). The applicability of the prediction equation was tested on individuals who were less than the 10(th) centile or greater than the 90(th) centile for stature, body mass and BMI. RESULTS: All independent variables were statistically significant (P<0.05) predictors of in(PP), adjusted R(2)=0.93 and all but gender were significant predictors for in(TMW), adjusted R(2)=0.95. However, measured in(PP) and in(TMW) were significantly lower than predicted in(PP) and in(TMW) for subjects >90th centile for stature, body mass, or BMI. CONCLUSIONS: the prediction equations overestimated PP and TMW in children, adolescents and young adults who were heavier than the reference subjects, as indicated by a relatively high body mass or high BMI for age or were taller than the reference subjects. The findings might reflect a deficit in anaerobic capacity in children, adolescents and young adults with relatively large body size for their age.

The G2/M regulator 14-3-3sigma prevents apoptosis through sequestration of Bax.

In response to DNA damage and genotoxic stress, the p53 tumor suppressor triggers either cell cycle arrest or apoptosis. The G(2) arrest after damage is, in part, mediated by the p53 target, 14-3-3final sigma (final sigma). Colorectal tumor cells lacking final sigma are exquisitely sensitive to DNA damage. Here we analyzed the mechanism of this sensitivity in final sigma(-/-) as compared with final sigma(+/+) human colorectal tumor cells. Exposure to adriamycin resulted in rapid apoptosis only in final sigma(-/-) cells. This was further characterized by caspase-3 activation, p21(CIP1) cleavage, and CDK2 activation. Moreover, Bax was rapidly translocated out of the cytoplasm, and cytochrome c was released in final sigma(-/-) cells. Transient adenovirus-mediated reconstitution of final sigma in the final sigma(-/-) cells led to effective rescue of this phenotype and protected cells against apoptosis. The association of final sigma, Bax, and CDK1 in protein complexes may be the basis for this antiapoptotic mechanism. In conclusion, final sigma not only enforces the p53-dependent G(2) arrest but also delays the apoptotic signal transduction.

Paramecium calmodulin mutants defective in ion channel regulation associate with melittin in the absence of calcium but require it for tertiary collapse.

Calmodulin (CaM) is a small acidic protein essential to calcium-mediated signal transduction. Conformational change driven by calcium binding controls its selective activation of myriad target proteins. In most well characterized cases, both homologous domains of CaM interact with a target protein. However, physiologically separable roles for the two domains were demonstrated by mutants of Paramecium tetraurelia [Kung, C. et al. (1992) Cell Calcium 13, 413], some of which have altered calcium affinities [Jaren, O. R. et al. (2000) Biochemistry 39, 6881]. To determine whether these mutants can associate with canonical targets in a calcium-dependent manner, their ability to bind melittin was assessed using analytical gel permeation chromatography, analytical ultracentrifugation, and fluorescence spectroscopy. The Stokes radius of wild-type PCaM and 11 of the mutants decreased dramatically upon binding melittin in the presence of calcium. Fluorescence spectra and sedimentation velocity studies showed that melittin bound to wild-type PCaM and mutants in a calcium-independent manner. However, there were domain-specific perturbations. Mutations in the N-domain of PCaM did not affect the spectrum of melittin (residue W19) under apo or calcium-saturated conditions, whereas most of the mutations in the C-domain did. These data are consistent with a calcium-dependent model of sequential target association whereby melittin (i) binds to the C-domain of PCaM in the absence of calcium, (ii) remains associated with the C-domain upon calcium binding to sites III and IV, and (iii) subsequently binds to the N-domain upon calcium binding to sites I and II of CaM, causing tertiary collapse.

Identification of CIP-1-associated regulator of cyclin B (CARB), a novel p21-binding protein acting in the G2 phase of the cell cycle.

The cyclin-dependent kinase inhibitor p21(cip1) regulates cell cycle progression, DNA replication, and DNA repair by binding to specific cellular proteins through distinct amino- and carboxyl-terminal protein binding motifs. We have identified a novel human gene, CARB (CIP-1-associated regulator of cyclin B), whose product interacts with the p21 carboxyl terminus. Immunocytochemical analysis demonstrates that the CARB protein is perinuclear and predominantly associated with the centrosome and mitotic spindle poles. In addition, CARB is also able to associate with cyclin B1, a key regulator of mitosis. However, cyclin B1-CARB complex formation occurs preferentially in the absence of p21. Unexpectedly, overexpression of CARB is associated with a growth-inhibitory and ultimately lethal phenotype in p21(-/-) cells but not in p21(+/+) cells. These data identify a novel mechanism that may underlie the effects of p21 in the G(2)/M phases of the cell cycle.

Compatibility of dexamethasone sodium phosphate with hydromorphone hydrochloride or diphenhydramine hydrochloride.

The stability and compatibility of dexamethasone sodium phosphate and hydromorphone hydrochloride or diphenhydramine hydrochloride at various concentrations at room temperature was studied. Solutions containing equal volumes in the following ranges of concentrations were prepared: dexamethasone sodium phosphate 0-10 mg/mL, diphenhydramine hydrochloride 0-50 mg/mL, and hydromorphone hydrochloride 0-40 mg/mL. Samples of each combination were analyzed immediately after mixing and at 7 and 24 hours using a stability-indicating high-performance liquid chromatographic assay. The pH of each solution was measured, and each combination was visually inspected. Precipitation occurred in solutions containing dexamethasone and hydromorphone hydrochloride or diphenhydramine hydrochloride when equal volumes of the most concentrated solutions were mixed. Some of the combinations at lower concentrations were visually compatible, and more than 90% of the initial concentrations of both drugs (i.e., dexamethasone-hydromorphone and dexamethasone-diphenhydramine) remained in these compatible solutions. Dexamethasone is visually compatible with diphenhydramine or hydromorphone but only within specific concentration ranges. In visually compatible solutions, both drug combinations are stable for up to 24 hours at room temperature.

H2 histaminic receptors in rat cerebral cortex. 1. Binding of [3H]histamine.

Saturable binding of [3H]histamine in equilibrium with homogenates of rat cerebral cortex reveals Hill coefficients between 0.4 and 1.0, depending upon the conditions. Data from individual experiments are well described assuming one or two classes of sites. Only the sites of higher affinity (KP1 = 3.9 +/- 0.5 nM) are observed when binding is measured by isotopic dilution at a low concentration of the radioligand (less than 1.5 nM) in the presence of magnesium or by varying the concentration of the radioligand. The sites of lower affinity (KP2 = 221 +/- 26 nM) appear during isotopic dilution at higher concentrations of the radioligand or at lower concentrations either upon the addition of guanylyl imidodiphosphate (GMP-PNP) or upon the removal of magnesium. Estimates of the second- and first-order rate constants for association and dissociation of [3H]histamine agree well with KP1. Apparent capacities corresponding to KP1 and KP2 are of the order of 100 ([R1]t) and 1300 pmol/g of protein ([R2]t), respectively. Simple interconversion cannot account for the changes in binding that occur upon adding GMP-PNP or removing magnesium, since the increase in [R2]t exceeds the decrease in [R1]t. Moreover, the apparent amount of high-affinity complex exhibits a biphasic dependence on the concentration of [3H]histamine; an increase at low concentrations is offset by a decrease that occurs at higher concentrations. The latter appears to be positively cooperative and concomitant with formation of the low-affinity complex. These and other observations indicate that the binding of histamine is inconsistent with models commonly invoked to rationalize the binding of agonists to neurohumoral receptors. GMP-PNP and magnesium reciprocally alter capacity at the sites of higher affinity, however, and the reduction caused by GMP-PNP reflects a substantial increase in the rate constant for dissociation at the sites that appear to be lost. The sites labeled by [3H]histamine thus reveal the properties of neurohumoral receptors linked to a nucleotide-specific G/F protein.

Liquid chromatographic analysis of sulfaquinoxaline and its application to pharmacokinetic studies in rabbits.

A specific, sensitive high-performance liquid chromatographic method is described for sulfaquinoxaline (I) and its major metabolite, the N4-acetyl metabolite (II), in biological fluids. Detection limits for I and II were 0.25 and 0.50 micrograms/mL in plasma and 0.10 and 0.20 micrograms/mL in urine, respectively. The pharmacokinetics of sulfaquinoxaline and its metabolite were studied in New Zealand White rabbits after individual doses of 50 mg/kg of sulfaquinoxaline and its metabolite were administered intravenously. Mean (+/- SD) plasma half-lives were 12.7 (8.0) h for sulfaquinoxaline and 15.4 (3.5) h for the metabolite. After administration of the N-acetyl metabolite sulfaquinoxaline appeared in the plasma and urine indicating that deacetylation had occurred. The repercussions of this observation are briefly discussed with respect to two rabbits in which plasma analyses and complete urine collections were made. As sulfaquinoxaline is administered prophylactically to rabbits by some breeders, it is recommended that investigators allow a washout period of about one week after receipt of the animals.

Indocyanine green pharmacokinetics in the rabbit.

In a Latin square design, nine New Zealand white male rabbits (2.8-4.8 kg) each received intravenous indocyanine green (ICG) in doses of 2.5, 12.5, and 25 mg/kg. A period of 4 weeks separated consecutive experiments. A specific high-pressure liquid chromatographic (HPLC) assay and the traditional spectrophotometric (SPEC) method were used to monitor plasma ICG. The analyses demonstrated the ambiguous nature of the SPEC assay, and the HPLC procedure pointed to the presence of an unidentified ICG metabolite. Dose-dependent ICG disposition was evident from the ANOVA of the mean (+/- SD) clearances, namely, 17.09 (7.35), 4.50 (0.82), and 2.27 (0.57) mL X min-1 X kg-1 for the aforementioned doses, respectively. Analysis of variance of the clearances also demonstrated a significant ordering effect suggesting cumulative ICG toxicity. The mean ICG profiles for the three doses accorded with a novel three-compartment model containing two ICG distributional spaces in addition to a compartment (liver) responsible for ICG elimination from the circulation. A saturable uptake process into the eliminating compartment (Vmax = 0.93 mg X kg-1 X min-1; Km = 31.9 mg/L) accounted for the dose-dependent features. Additional studies in four unanesthetized rabbits with chronically catheterized bile ducts revealed no disparity between the SPEC and HPLC analyses of biliary ICG. The mean (+/- SD) ICG recovery in bile following an intravenous dose of about 12.5 mg/kg was 59.8 (16.3)%.