Changes in umbilical venous velocities with physiologic perturbations.

OBJECTIVE: The purpose of this study was to determine the direction of transmission of umbilical venous Doppler flow velocity changes in human fetuses. STUDY DESIGN: Strip chart recordings of simultaneously measured umbilical arterial and venous velocities were examined at two sites in the umbilical cord, one near the fetus (proximal) and one near the placenta (distal). Fetuses with venous pulsations or breathing episodes were included. At both locations time from venous pulsation to arterial systole was measured in fetuses with venous pulsations and duration of phase delay between arterial diastolic velocity minimum and venous velocity minimum was measured in fetuses with breathing episodes. RESULTS: In 21 fetuses with venous pulsations the pulsations occurred earlier in the cardiac cycle at proximal sites (0.12 +/- 0.04 second before systole) and later at distal sites (0.02 +/- 0.04 second before systole;P <.001). Phase delays in venous velocities in the 5 fetuses with breathing episodes were also longer at distal sites than at proximal sites (P <.011). CONCLUSION: Changes in umbilical venous velocities occurred earlier at sites that were closer to the fetus. These findings suggest that changes in umbilical venous velocities originate in the fetal venous system and are transmitted to, rather than from, the placenta.

Vapor pressure osmometry studies of osmolyte-protein interactions: implications for the action of osmoprotectants in vivo and for the interpretation of "osmotic stress" experiments in vitro.

To interpret or to predict the responses of biopolymer processes in vivo and in vitro to changes in solute concentration and to coupled changes in water activity (osmotic stress), a quantitative understanding of the thermodynamic consequences of interactions of solutes and water with biopolymer surfaces is required. To this end, we report isoosmolal preferential interaction coefficients (Gamma(mu1) determined by vapor pressure osmometry (VPO) over a wide range of concentrations for interactions between native bovine serum albumin (BSA) and six small solutes. These include Escherichia coli cytoplasmic osmolytes [potassium glutamate (K(+)Glu(-)), trehalose], E. coli osmoprotectants (proline, glycine betaine), and also glycerol and trimethylamine N-oxide (TMAO). For all six solutes, Gamma(mu1) and the corresponding dialysis preferential interaction coefficient Gamma(mu1),(mu3) (both calculated from the VPO data) are negative; Gamma(mu1), (mu3) is proportional to bulk solute molality (m(bulk)3) at least up to 1 m (molal). Negative values of Gamma(mu1),(mu3) indicate preferential exclusion of these solutes from a BSA solution at dialysis equilibrium and correspond to local concentrations of these solutes in the vicinity of BSA which are lower than their bulk concentrations. Of the solutes investigated, betaine is the most excluded (Gamma(mu1),(mu3)/m(bulk)3 = -49 +/- 1 m(-1)); glycerol is the least excluded (Gamma(mu1),(mu3)/m(bulk)3 = -10 +/- 1 m(-1)). Between these extremes, the magnitude of Gamma(mu1),(mu3)/m(bulk)3 decreases in the order glycine betaine >> proline >TMAO > trehalose approximately K(+)Glu(-) > glycerol. The order of exclusion of E. coli osmolytes from BSA surface correlates with their effectiveness as osmoprotectants, which increase the growth rate of E. coli at high external osmolality. For the most excluded solute (betaine), Gamma(mu1),(mu3) provides a minimum estimate of the hydration of native BSA of approximately 2.8 x 10(3) H(2)O/BSA, which corresponds to slightly less than a monolayer (estimated to be approximately 3.2 x 10(3) H(2)O). Consequently, of the solutes investigated here, only betaine might be suitable for use in osmotic stress experiments in vitro as a direct probe to quantify changes in hydration of protein surface in biopolymer processes. More generally, however, our results and analysis lead to the proposal that any of these solutes can be used to quantify changes in water-accessible surface area (ASA) in biopolymer processes once preferential interactions of the solute with biopolymer surface are properly taken into account.

The importance of coulombic end effects: experimental characterization of the effects of oligonucleotide flanking charges on the strength and salt dependence of oligocation (L8+) binding to single-stranded DNA oligomers.

Binding constants Kobs, expressed per site and evaluated in the limit of zero binding density, are quantified as functions of salt (sodium acetate) concentration for the interactions of the oligopeptide ligand KWK6NH2 (designated L8+, with ZL = 8 charges) with three single-stranded DNA oligomers (ss dT-mers, with |ZD| = 15, 39, and 69 charges). These results provide the first systematic experimental information about the effect of changing |ZD| on the strength and salt dependence of oligocation-oligonucleotide binding interactions. In a comparative study of L8+ binding to poly dT and to a short dT oligomer (|ZD| = 10),. Proc. Natl. Acad. Sci. USA. 93:2511-2516) demonstrated the profound thermodynamic effects of phosphate charges that flank isolated nonspecific L8+ binding sites on DNA. Here we find that both Kobs and the magnitude of its power dependence on salt activity (|SaKobs|) increase monotonically with increasing |ZD|. The dependences of Kobs and SaKobs on |ZD| are interpreted by introducing a simple two-state thermodynamic model for Coulombic end effects, which accounts for our finding that when L8+ binds to sufficiently long dT-mers, both DeltaGobso = -RT ln Kobs and SaKobs approach the values characteristic of binding to poly-dT as linear functions of the reciprocal of the number of potential oligocation binding sites on the DNA lattice. Analysis of our L8+-dT-mer binding data in terms of this model indicates that the axial range of the Coulombic end effect for ss DNA extends over approximately 10 phosphate charges. We conclude that Coulombic interactions cause an oligocation (with ZL < |ZD|) to bind preferentially to interior rather than terminal binding sites on oligoanionic or polyanionic DNA, and we quantify the strong increase of this preference with decreasing salt concentration. Coulombic end effects must be considered when oligonucleotides are used as models for polyanionic DNA in thermodynamic studies of the binding of charged ligands, including proteins.

Umbilical venous velocity pulsations are related to atrial contraction pressure waveforms in fetal lambs.

OBJECTIVE: To identify the source of umbilical venous velocity pulsations, times of transmission from the atrial contraction pressure waveform to velocity waves in the inferior vena cava, ductus venosus, intra-abdominal umbilical vein, and intra-amniotic umbilical vein were examined. METHODS: Five lamb fetuses at 125-135 days' gestation were instrumented with solid state pressure transducers in the inferior vena cava, fluid-filled catheters in the inferior vena cava and descending aorta, and epicardial pacemakers. Three to 5 days postoperatively, inferior vena cava, ductus venosus, and umbilical vein velocities were examined with Doppler ultrasound. Normal saline was administered and umbilical vein velocity pulsations developed (180 +/- 60 mL). In three fetuses, premature atrial contractions were induced under baseline conditions and after umbilical vein velocity pulsations developed. RESULTS: Times of transmission from the atrial contraction pressure waveform until velocity decreases in the fetal venous system were significantly different in the inferior vena cava, ductus venosus, intra-abdominal umbilical vein, and intra-amniotic umbilical vein (P < .001). Times increased with the distance from the atrium. Inferior vena cava pressure increased with fluid administration from 3.7 +/- 4.7 mmHg to 9.3 +/- 2.3 mmHg (P < .01). Time from increased pressure waveforms with induced premature atrial contractions to the nadir of subsequent umbilical vein velocity waves decreased from 0.123 +/- 0.047 seconds before saline administration to 0.072 +/- 0.039 seconds after saline administration (P < .001). CONCLUSION: Transmission time of atrial pressure into the venous circulation increases with distance from the atrium and decreases with volume loading. Umbilical venous velocity pulsations derive from atrial pressure changes transmitted in a retrograde fashion.

Binding of cationic (+4) alanine- and glycine-containing oligopeptides to double-stranded DNA: thermodynamic analysis of effects of coulombic interactions and alpha-helix induction.

Coulombic interactions and coupled conformational changes make important contributions to stability and specificity of many protein-nucleic acid complexes. As models of these phenomena in simpler systems, we have investigated the binding to mononucleosomal (160 base-pair) calf thymus DNA of a high charge density (compact) 5-residue (+4) oligopeptide (with 4 lysines and 1 tryptophan) and of four lower charge density (extended) 17-residue (+4) oligopeptides (each with 4 lysines, 10-12 alanines, 0-2 glycines, and 1 tryptophan). The fractional helicity (f(h)) of each oligopeptide before and after DNA binding was determined using circular dichroism. At low univalent cation concentration ([M+] = 6.4 mM), binding to DNA increases f(h) significantly for all but one of the extended oligopeptides. Oligopeptide-DNA binding constants (K(obs)) and apparent binding site sizes (n) were quantified using the noncooperative McGhee-von Hippel isotherm to fit tryptophan fluorescence quenching data. For each of the oligopeptides studied, n is found to be approximately equal to four, the number of lysine charges. In the range 6.4 mM < or = [M+] < or = 21.5 mM, power dependences of K(obs) on [M+] (SK(obs) = d log K(obs)/d log[M+]) for all 17-residue (+4) oligopeptides are similar with an average value of -3.7 +/- 0.4, which is indistinguishable (outside uncertainty) from the value obtained here for the compact (+4) oligopeptide and from values reported elsewhere for another compact tetralysine and for spermine (+4). Our results are consistent with the conclusion that the nonspecific binding to DNA of all these tetravalent ligands is driven primarily by coulombic interactions. At any [M+] investigated, values of K(obs) for the four extended (+4) oligopeptides differ by less than an order of magnitude, but all are 1-2 orders of magnitude less than values of K(obs) for two compact (+4) oligopeptides and for spermine. The differences in K(obs) for oligopeptide-DNA complexes, which all have similar n and similar SK(obs) indicate that when an extended oligopeptide binds to DNA it becomes more compact as a result of conformational changes, such as the additional alpha-helix formation detected by circular dichroism.