Long ECGs reveal rich and robust dynamical regimes in patients with frequent ectopy

We have analyzed the electrocardiographic data collected during continuous 7-day ambulatory recordings in patients with frequent premature ventricular complexes (PVCs). We analyze the dependence of the frequency and patterns of PVCs on the heart rate and the time of the day. Patients display rhythms of a complex yet consistent structure. In a given patient, the pattern remains robust over different days and particular repetitive patterns appear at specific heart rates, suggesting the appearance of bifurcations in the dynamics. Over the course of 24 h, we find that in some patients, patterns appear to depend only on the heart rate, whereas in others, both the time of the day and the heart rate play a role in controlling the dynamics. Identifying parameter values at which bifurcations occur facilitates the development of dynamical models for arrhythmia. The use of powerful recording and analysis techniques will enable improved analysis of data and better understanding of mechanisms of arrhythmia in individual patients.

Fibromyalgia beyond reductionism. Heart rhythm fractal analysis to assess autonomic nervous system resilience

OBJECTIVES

The prevailing linear reductionist medical model seems unable to explain complex multisymptomatic illnesses such as fibromyalgia (FM) and similar maladies. Paradigms derived from the complexity theory may provide a coherent framework for these elusive illnesses. Along these lines is the proposal that FM represents a degradation of our main complex adaptive system (the autonomic nervous system, ANS), in a failed effort to adjust to a hostile environment. Healthy complex systems have fractal structures. Heart rate fractal-like variability reflects resilient ANS performance. Our aim was to measure the heart rate variability (HRV) fractal scaling index in FM patients and to correlate this index with clinical symptoms.

METHOD

We studied 30 women with FM and 30 controls. All participants filled out questionnaires assessing the severity of FM. The HRV fractal scaling index was estimated during 24 h using detrended fluctuation analysis (DFA).

RESULTS

The fractal scaling index alpha-1 was higher in FM patients than in controls (mean ± sd: 1.22 ± 0.10 vs. 1.16 ± 0.09; p = 0.031). There was a positive correlation between the fractal scaling index alpha-1 and the visual analogue scale (VAS) for depression (Spearman's ρ = 0.36, p = 0.04).

CONCLUSIONS

The heart rate fractal exponent alpha-1 is altered in FM patients, suggesting a rigid ANS performance. This tangible non-linear finding supports the notion that FM may represent a degradation of our main complex adaptive system, namely the ANS.

Cytochrome aa3 of Rhodobacter sphaeroides as a model for mitochondrial cytochrome c oxidase. Purification, kinetics, proton pumping, and spectral analysis

Aerobically grown Rhodobacter sphaeroides synthesizes a respiratory chain similar to that of eukaryotes. We describe the purification of the aa3-type cytochrome c oxidase of Rb. sphaeroides as a highly active (Vmax > or = 1800 s-1), three-subunit enzyme from isolated, washed cytoplasmic membranes by hydroxylapatite chromatography and anion exchange fast protein liquid chromatography. The purified oxidase exhibits biphasic kinetics of oxidation of mammalian cytochrome c, similar to mitochondrial oxidases, and pumps protons efficiently (H+/e- = 0.7) following reconstitution into phospholipid vesicles. A membrane-bound cytochrome c is associated with the aa3-type oxidase in situ, but is removed during purification. The EPR spectra of the Rb. sphaeroides enzyme suggest the presence of a strong hydrogen bond to one or both of the histidine ligands of heme a. In other respects, optical, EPR, and resonance Raman analyses of the metal centers and their protein environments demonstrate a close correspondence between the bacterial enzyme and the structurally more complex bovine cytochrome c oxidase. The results establish this bacterial oxidase as an excellent model system for the mammalian enzyme and provide the basis for site-directed mutational analysis of its energy transducing function.

Betaine deficiency in maize : complementation tests and metabolic basis

Maize (Zea mays L.) is a betaine-accumulating species, but certain maize genotypes lack betaine almost completely; a single recessive gene has been implicated as the cause of this deficiency (D Rhodes, PJ Rich [1988] Plant Physiol 88: 102-108). This study was undertaken to determine whether betaine deficiency in diverse maize germplasm is conditioned by the same genetic locus, and to define the biochemical lesion(s) involved. Complementation tests indicated that all 13 deficient genotypes tested shared a common locus. One maize population (P77) was found to be segregating for betaine deficiency, and true breeding individuals were used to produce related lines with and without betaine. Leaf tissue of both betaine-positive and betaine-deficient lines readily converted supplied betaine aldehyde to betaine, but only the betaine-containing line was able to oxidize supplied choline to betaine. This locates the lesion in betaine-deficient plants at the choline --> betaine aldehyde step of betaine synthesis. Consistent with this location, betaine-deficient plants were shown to have no detectable endogenous pool of betaine aldehyde.

Oxygen-18 and deuterium labeling studies of choline oxidation by spinach and sugar beet

Chenopods synthesize betaine by a two-step oxidation of choline: choline --> betaine aldehyde --> betaine. The pathway is chloroplastic; the first step has been shown in isolated spinach (Spinacia oleracea L.) chloroplasts to be O(2)- and light-dependent, the role of light being to provide reducing power (P Weigel, EA Weretilnyk, AD Hanson 1988 Plant Physiol 86: 54-60). Here, we report use of in vivo(18)O- and (2)H-labeling in conjunction with fast atom bombardment mass spectrometry to test for two hypothetical choline-oxidizing reactions that would explain the observed requirements for O(2) and reductant: a desaturase or an oxygenase. Simple syntheses for (2)H(3)-choline, (2)H(3), (18)O-choline, and (2)H(3), (18)O-betaine are given. A desaturase mechanism was sought by giving choline deuterated at the 2-carbon, or choline unlabeled at this position together with (2)H(2)O and by analyzing newly synthesized betaine. About 15% of the (2)H at C-2 was lost during oxidation of choline to betaine, and about 10% of the betaine made in the presence of 50% (2)H(2)O was monodeuterated. These small effects are more consistent with chemical exchange than with a desaturase, because 10 to 15% losses of (2)H from the C-2 position also occurred if choline was converted to betaine by a purified bacterial choline oxidase. To test for an oxygenase, the incorporation of (18)O from (18)O(2) into newly synthesized betaine was compared with that from (18)O-labeled choline, in light and darkness. Incorporation of (18)O from (18)O-choline was readily detectable and varied from about 15 to 50% of the theoretical maximum value; the (18)O losses were attributable to exchange of the intermediate betaine aldehyde with water. In darkness, incorporation of (18)O from (18)O(2) approached that from (18)O-choline, but in the light was severalfold lower, presumably due to isotopic dilution by photosynthetic (16)O(2). These data indicate that the chloroplast choline-oxidizing enzyme is an oxygenase.

Choline oxidation by intact spinach chloroplasts

Plants synthesize betaine by a two-step oxidation of choline (choline --> betaine aldehyde --> betaine). Protoplast-derived chloroplasts of spinach (Spinacia oleracea L.) carry out both reactions, more rapidly in light than in darkness (AD Hanson et al. 1985 Proc Natl Acad Sci USA 82: 3678-3682). We investigated the light-stimulated oxidation of choline, using spinach chloroplasts isolated directly from leaves. The rates of choline oxidation obtained (dark and light rates: 10-50 and 100-300 nanomoles per hour per milligram chlorophyll, respectively) were approximately 20-fold higher than for protoplast-derived chloroplasts. Betaine aldehyde was the main product. Choline oxidation in darkness and light was suppressed by hypoxia. Neither uncouplers nor the Calvin cycle inhibitor glyceraldehyde greatly affected choline oxidation in the light, and maximal choline oxidation was attained far below light saturation of CO(2) fixation. The light stimulation of choline oxidation was abolished by the PSII inhibitors DCMU and dibromothymoquinone, and was partially restored by adding reduced diaminodurene, an electron donor to PSI. Both methyl viologen and phenazine methosulfate prevented choline oxidation. Adding dihydroxyacetone phosphate, which can generate NADPH in organello, doubled the dark rate of choline oxidation. These results indicate that choline oxidation in chloroplasts requires oxygen, and reducing power generated from PSI. Enzymic reactions consistent with these requirements are discussed.

Preparation of a highly active ATPase of the mesophilic cyanobacterium Spirulina maxima

In this work, we report new studies on the ATPase attached to the photosynthetic membranes of the mesophilic cyanobacterium Spirulina maxima. This enzyme does not display persistent latency as had been previously reported for the ATPase of Spirulina platensis. The enzyme is readily activated by the careful application of methods currently used to activate chloroplast CF1. Photosynthetic membranes of Spirulina maxima show a Mg(2+)-dependent ATPase activity of 195±25 μmol Pi (mg chl)(-1) h(-1) after a light plus dithiothreitol (DDT) treatment. Methanol treatment of these membranes elicits Mg(2+)-dependent ATPase activity of 222±18 μmol Pi (mg chl)(-1) h(-1).Here, we also describe the purification of the soluble coupling factor AF1 of Spirulina maxima. This enzyme is unique among mesophilic cyanobacterial F1 preparations in regard to its high specific Ca(2+)-dependent ATPase activity after heat treatment (14.75±1.91 μmol Pi (mg prot)(-1) min(-1)) and its room temperature stability.