Anionic biopolyelectrolytes of the syndecan/perlecan superfamily: physicochemical properties and medical significance

In the review article presented here, we demonstrate that the connective tissue is more than just a matrix for cells and a passive scaffold to provide physical support. The extracellular matrix can be subdivided into proteins (collagen, elastin), glycoconjugates (structural glycoproteins, proteoglycans) and glycosaminoglycans (hyaluronan). Our main focus rests on the anionic biopolyelectrolytes of the perlecan/syndecan superfamily which belongs to extracellular matrix and cell membrane integral proteoglycans. Though the extracellular domain of the syndecans may well be performing a structural role within the extracellular matrix, a key function of this class of membrane intercalated proteoglycans may be to act as signal transducers across the plasma membrane and thus be more appropriately included in the group of cell surface receptors. Nevertheless, there is a continuum in functions of syndecans and perlecans, especially with respect to their structural role and biomedical significance. HS/CS proteoglycans are receptor sites for lipoprotein binding thus intervening directly in lipid metabolism. We could show that among all lipoproteins, HDL has the highest affinity to these proteoglycans and thus instals a feedforward forechecking loop against atherogenic apoB100 lipoprotein deposition on surface membranes and in subendothelial spaces. Therefore, HDL is not only responsible for VLDL/IDL/LDL cholesterol exit but also controls thoroughly the entry. This way, it inhibits arteriosclerotic nanoplaque formation. The ternary complex 'lipoprotein receptor (HS/CS-PG) - lipoprotein (LDL, oxLDL, Lp(a)) - calcium' may be interpreted as arteriosclerotic nanoplaque build-up on the molecular level before any cellular reactivity, possibly representing the arteriosclerotic primary lesion combined with endothelial dysfunction. With laser-based ellipsometry we could demonstrate that nanoplaque formation is a Ca(2+)-driven process. In an in vitro biosensor application of HS-PG coated silica surfaces we tested nanoplaque formation and size in clinical trials with cardiovascular high-risk patients who underwent treatment with ginkgo or fluvastatin. While ginkgo reduced nanoplaque formation (size) by 14.3% (23.4%) in the isolated apoB100 lipid fraction at a normal blood Ca(2+) concentration, the effect of the statin with a reduction of 44.1% (25.4%) was more pronounced. In addition, ginkgo showed beneficial effects on several biomarkers of oxidative stress and inflammation. Besides acting as peripheral lipoprotein binding receptor, HS/CS-PG is crucially implicated in blood flow sensing. A sensor molecule has to fulfil certain mechanochemical and mechanoelectrical requirements. It should possess viscoelastic and cation binding properties capable of undergoing conformational changes caused both mechanically and electrostatically. Moreover, the latter should be ion-specific. Under no-flow conditions, the viscoelastic polyelectrolyte at the endothelium - blood interface assumes a random coil form. Blood flow causes a conformational change from the random coil state to the directed filament structure state. This conformational transition effects a protein unfurling and molecular elongation of the GAG side chains like in a 'stretched' spring. This configuration is therefore combined with an increase in binding sites for Na(+) ions. Counterion migration of Na(+) along the polysaccharide chain is followed by transmembrane Na(+) influx into the endothelial cell and by endothelial cell membrane depolarization. The simultaneous Ca(2+) influx releases NO and PGI2, vasodilatation is the consequence. Decrease in flow reverses the process. Binding of Ca(2+) and/or apoB100 lipoproteins (nanoplaque formation) impairs the flow sensor function. The physicochemical and functional properties of proteoglycans are due to their amphiphilicity and anionic polyelectrolyte character. Thus, they potently interact with cations, albeit in a rather complex manner. Utilizing (23)Na(+) and (39)K(+) NMR techniques, we could show that, both in HS-PG solutions and in native vascular connective tissue, the mode of interaction for monovalent cations is competition. Mg(2+) and Ca(2+) ions, however, induced a conformational change leading to an increased allosteric, cooperative K(+) and Na(+) binding, respectively. Since extracellular matrices and basement membranes form a tight-fitting sheath around the cell membrane of muscle and Schwann cells, in particular around sinus node cells of the heart, and underlie all epithelial and endothelial cell sheets and tubes, a release of cations from or an adsorption to these polyanionic macromolecules can transiently lead to fast and drastic activity changes in these tiny extracellular tissue compartments. The ionic currents underlying pacemaker and action potential of sinus node cells are fundamentally modulated. Therefore, these polyelectrolytic ion binding characteristics directly contribute to and intervene into heart rhythm.

Comparison of Non-invasive and Invasive Arterial Blood Pressure Measurement for Assessment of Dynamic Cerebral Autoregulation

BACKGROUND

There is a growing interest in measuring cerebral autoregulation in patients with acute brain injury. Non-invasive finger photo-plethysmography (Finapres) is the method of choice to relate arterial blood pressure to changes in cerebral blood flow. Among acutely ill patients, however, peripheral vasoconstriction often limits the use of Finapres requiring direct intravascular blood pressure measurement. We evaluated how these two different forms of blood pressure monitoring affect the parameters of dynamic cerebral autoregulation (DCA).

METHODS

We performed 37 simultaneous recordings of BP and cerebral blood flow velocity in 15 patients with acute brain injury. DCA was estimated in the frequency domain using transfer function analysis to calculate phase shift, gain, and coherence. In addition the mean velocity index (Mx) was calculated for assessment of DCA in the time domain.

RESULTS

The mean patient age was 58.1 ± 15.9 years, 80 % (n = 12) were women. We found good inter-method agreement between Finapres and direct intravascular measurement using Bland-Altman and correlation analyses. Finapres gives higher values for the efficiency of dynamic CA compared with values derived from radial artery catheter, as indicated by biases in the phase (26.3 ± 11.6° vs. 21.7 ± 10.5°, p = 0.001) and Mx (0.571 ± 0.137 vs. 0.649 ± 0.128, p < 0.001). Gain in the low frequency range did not significantly differ between the two arterial blood pressure methods. The average coherence between CBFV and ABP was higher when BP was measured with arterial catheter for frequencies above 0.05 Hz (0.8 vs. 0.73, p < 0.001).

CONCLUSION

Overall, both methods yield similar results and can be used for the assessment of DCA. However, there was a small but significant difference for both mean Mx and phase shift, which would need to be adjusted for during monitoring of patients when using both methods. When available, invasive arterial blood pressure monitoring may improve accuracy and thus should be the preferred method for DCA assessment in the ICU.

Vasomotion - what is currently thought?

This minireview discusses vasomotion, which is the oscillation in tone of blood vessels leading to flowmotion. We will briefly discuss the prevalence of vasomotion and its potential physiological and pathophysiological relevance. We will also discuss the models that have been suggested to explain how a coordinated oscillatory activity of the smooth muscle tone can occur and emphasize the role of the endothelium, the handling of intracellular Ca(2+) and the role of smooth muscle cell ion conductances. It is concluded that vasomotion is likely to enhance tissue dialysis, although this concept still requires more experimental verification, and that an understanding at the molecular level for the pathways leading to vasomotion is beginning to emerge.

Vasomotion: cellular background for the oscillator and for the synchronization of smooth muscle cells

1. Vasomotion is the oscillation of vascular tone with frequencies in the range from 1 to 20 min(-1) seen in most vascular beds. The oscillation originates in the vessel wall and is seen both in vivo and in vitro. 2. Recently, our ideas on the cellular mechanisms responsible for vasomotion have improved. Three different types of cellular oscillations have been suggested. One model has suggested that oscillatory release of Ca2+ from intracellular stores is important (the oscillation is based on a cytosolic oscillator). A second proposed mechanism is an oscillation originating in the sarcolemma (a membrane oscillator). A third mechanism is based on an oscillation of glycolysis (metabolic oscillator). For the two latter mechanisms, only limited experimental evidence is available. 3. To understand vasomotion, it is important to understand how the cells synchronize. For the cytosolic oscillators synchronization may occur via activation of Ca2+-sensitive ion channels by oscillatory Ca2+ release. The ensuing membrane potential oscillation feeds back on the intracellular Ca2+ stores and causes synchronization of the Ca2+ release. While membrane oscillators in adjacent smooth muscle cells could be synchronized through the same mechanism that sets up the oscillation in the individual cells, a mechanism to synchronize the metabolic-based oscillators has not been suggested. 4. The interpretation of the experimental observations is supported by theoretical modelling of smooth muscle cells behaviour, and the new insight into the mechanisms of vasomotion has the potential to provide tools to investigate the physiological role of vasomotion.

Heart rate variability: origins, methods, and interpretive caveats

Components of heart rate variability have attracted considerable attention in psychology and medicine and have become important dependent measures in psychophysiology and behavioral medicine. Quantification and interpretation of heart rate variability, however, remain complex issues and are fraught with pitfalls. The present report (a) examines the physiological origins and mechanisms of heart rate variability, (b) considers quantitative approaches to measurement, and (c) highlights important caveats in the interpretation of heart rate variability. Summary guidelines for research in this area are outlined, and suggestions and prospects for future developments are considered.

Effects of aging on blood pressure variability in resting conditions

The objective of this study was to determine the effect of aging on beat-to-beat blood pressure and pulse interval variability in resting conditions and to determine the effect of aging on the sympathetic and vagal influence on the cardiovascular system by power spectral analysis of blood pressure and pulse interval. We studied three groups of healthy, normotensive subjects: young (10 to 15 years, n = 16), adult (20 to 40 years, n = 16), and elderly (70 to 90 years, n = 25). Beat-to-beat blood pressure was measured by Finapres during 20 minutes supine and 10 minutes standing. Overall systolic and diastolic blood pressures and pulse interval variability were determined as SD and as coefficient of variation. Also, relative powers of the mid-frequency (0.08 to 0.12 Hz) and high-frequency bands (0.15 to 0.40 Hz) were determined by spectral analysis. In these subjects no differences in blood pressure variability (either as SD or coefficient of variation) were found between age groups, except for the coefficient of variation of standing diastolic blood pressure, which decreased with aging. Pulse interval variability decreased with aging. Power of the mid-frequency band of systolic and diastolic blood pressures was markedly decreased in the elderly, especially in the standing position. Power of the high-frequency band of pulse interval was also decreased in the elderly. Baroreflex sensitivity calculated by fast Fourier transformation spectral analysis was decreased in the elderly subjects compared with the younger groups. In conclusion, we found no change in the overall variability of blood pressure with aging. Mid-frequency spectral power of blood pressure and mid- and high-frequency spectral powers of pulse interval variability were decreased in the elderly. These results suggest that aging does not merely influence the magnitude of blood pressure and pulse interval variability but causes a complex rearrangement of the variability pattern by changes in neurocardiovascular regulation.

On the origin and dynamics of the vasomotion of small arteries

A system of differential equations describing stationary vasomotion is formulated. It incorporates the ionic transports, cell-membrane potential, muscle contraction of the vessel smooth muscle cells, and the mechanics of a thick-walled cylinder. It is shown that the interaction of Ca2+ and K+ fluxes mediated by voltage-gated and voltage-calcium-gated channels, respectively, brings about periodicity of those transports. This results on a time-periodic cytoplasmic calcium concentration, myosin light chains phosphorylation, and crossbridges formation with the attending muscle stress. The vessel's transmural pressure determines a hoop stress. The resultant hoop, elastic, and muscle stresses determine the rate of change of the vessel's diameter: vasomotion. The model results agree with the experimental observations. The sensitivity of the vasomotion's dependence on parameter values and its significance to experimental protocols are examined. Further, it is hypothesized that the dependence of calcium-channel openings on voltage is shifted by changes on transmural pressure. Thus, Harder's experimental results are reproduced, among them the decreasing of vessel diameter with increasing pressure. Those behaviors are associated with a pattern of change of the singularities of the system of equations describing the model. This suggests a functional relationship on the interactions of Ca2+ and K+ fluxes responsible for the myogenic response; it may not result from a single molecular mechanism. The model is constructed so that additional experimental information can be readily incorporated.

Spectral and sequence analysis of finger blood pressure variability. Comparison with analysis of intra-arterial recordings

The aim of our study was to assess whether the Finapres device is able to accurately monitor not only average blood pressure values but also blood pressure variability. To examine this issue, we analyzed 30-minute recordings of finger and intra-arterial pressure simultaneously obtained at rest in 14 patients. We compared systolic blood pressure, diastolic blood pressure, mean arterial pressure, pulse interval (the reciprocal of heart rate), overall variability (standard deviation), and specific time-domain and frequency-domain components. Systolic blood pressure, diastolic blood pressure, mean arterial pressure, and pulse interval spectral powers were computed by fast Fourier transform over three frequency bands: low frequency (0.025 to 0.07 Hz), midfrequency (0.07 to 0.14 Hz), and high frequency (0.14 to 0.35 Hz). The coherence, ie, the degree of association between blood pressure and pulse interval powers obtained by the two techniques, was also assessed. Standard deviations of diastolic blood pressure, mean arterial pressure, and pulse interval were similar when assessed from the two recordings, whereas standard deviation of systolic blood pressure was overestimated by analysis of finger pressure recordings. All powers of diastolic blood pressure and mean arterial pressure and high-frequency powers of systolic blood pressure estimated from analysis of finger blood pressure tracings were superimposable to those obtained by analyzing invasive recordings. Low-frequency and midfrequency powers of intra-arterial systolic blood pressure were significantly overestimated by the analysis of finger blood pressure tracings (+13.7 +/- 4.4 mm Hg2, P < .01, and +2.3 +/- 0.9 mm Hg2, P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolic correlates to pacemaker activity in the smooth muscle of guinea-pig mesotubarium

Oxygen consumption (FO2) and lactate production (Flac) were measured during spontaneous activity in the guinea-pig mesotubarium. During spontaneous contractions FO2 increased to maximally 0.270 +/- 0.025 mumol min-1g-1 (n = 23), followed by a rapid fall immediately upon relaxation. In the relaxed period (5-15 min) between spontaneous contractions FO2 continued to slowly decrease by about 25% towards a final value of 0.150 +/- 0.01 mumol min-1g-1. Flac showed no consistent variation during the relaxed period. Ouabain (10(-6)M) produced a contracture, which was abolished by the Ca2(+)-antagonist felodipine (10(-6)M). In the presence of felodipine, addition of ouabain caused depolarization and a decrease of oxygen consumption by 21% and of lactate production by 31%. Exchange of glucose in the physiological Krebs solution for beta-hydroxybutyrate did not influence spontaneous activity, while subsequent addition of cyanide (2 mM) abolished contractions and caused a hyperpolarization of 15 mV. Blockade of ATP-dependent K+ channels by addition of glibenclamide (10(-7)M) to the relaxed muscle in this situation caused spontaneous contractile activity to reappear. In glucose-containing Krebs solution glibenclamide had no effect on the spontaneous contractile and electrical activity and contractions persisted after addition of cyanide. The relaxing and hyperpolarizing effect of pinacidil could be counteracted by addition of glibenclamide. The results suggest that a decrease in electrogenic Na+/K(+)-pump activity in the course of the relaxed period between contractions could contribute to the pacemaker behaviour. ATP-dependent K+ channels, while having little influence on the spontaneous contractile activity under normal metabolic conditions, could be activated during blockade of aerobic and anaerobic metabolism, leading to inhibition of pacemaker activity.

The Prony spectral line estimation (PSLE) method for the analysis of vascular oscillations

The Prony spectral line estimation (PSLE) technique is implemented and tested on data consisting of sinusoids mixed with Gaussian noise and on recordings of oscillatory diameter changes (vasomotion) of arterioles. It is concluded that the PSLE method is well suited for the spectrum analysis of short oscillatory diameter records.

Poiseuille, periodicity, and perfusion: rhythmic oscillatory vasomotion in the skin

Cutaneous vasomotion has not been actively investigated until recently. This is hardly surprising, as it has not been a reproducible phenomenon. During recent studies on various physiological and pharmacological vascular problems, we identified experimental conditions in which cutaneous vasomotion commonly occurred. We then characterized four methods that routinely provoke human cutaneous vasomotion in vivo, in order to further characterize this physiological phenomenon. Although several adaptive advantages may exist for vasomotion, the most compelling theory can be derived mathematically from Poiseuille's law. Because the flow of a liquid through a vessel is proportional to the fourth power of the radius, it can be demonstrated that the resistance of a vessel with a constant diameter is greater than that of a vessel of the same average diameter in which the diameter changes sinusoidally. Importantly, the rhythmicity originates within the vascular tissue, and there appears to be electromechanical coupling. The cation effluxes demonstrate oscillatory behavior that may be driven by the availability of adenosine triphosphate. Substrate and product concentrations can alter the activity of the allosteric enzyme, phosphofructokinase, which may control the oscillations in ATP concentration. Despite the qualitatively different provocative agents, the cutaneous rhythmic oscillatory vasomotion always first appears after a peak in erythrocyte flux, and it disappears before reaching resting flux levels. Thus, cutaneous rhythmic oscillatory vasomotion is a midrange phenomenon, most likely corresponding to the "oscillatory domain" of glycolysis. Finally, a common feature of tissue preparations for the study of vasomotion is that anesthesia was not used. We have shown that this inhibitory effect of anesthetic agents may persist well beyond "anesthesia," and this suppression may be of clinical importance in the patient with microcirculatory compromise undergoing surgery.

Pressure-diameter relationships of segments of human finger arteries

Pressure-diameter relationships of segments of human finger arteries, aged 57-85 years, were measured in vitro. The arteries, obtained at autopsy within 48 h after death, were stored in glucose-free Tyrode at 4 degrees C. Experiments began within 40 h after autopsy. The diameter responses to various transmural pressure changes, with and without the addition of noradrenaline to the Tyrode solution in the specimen chamber, were compared with the responses of freshly excised rat tail arteries. In general, pressure-diameter relations of human finger artery segments were similar to those of rat tail artery segments, with a steep slope in the collapse region near zero pressure. Also, spontaneous rhythmic contractions and myogenic activity induced by high transmural pressures were similar to those observed in the fresh rat tail arteries. Human finger arteries, however, could contract to complete closure both spontaneously and after addition of noradrenaline, while rat tail arteries did not. The diameter changes of the arterial segments during forced 1 Hz oscillations of 20-50 mm Hg (2.7-6.7 kPa) amplitude superimposed on a mean transmural pressure were substantially smaller than those during quasi-steady inflation-deflation ramps over the same pressure range, indicating the presence of a strong viscous wall component.