Design and implementation of a protection system for NMR spectrometers.

We have implemented a scheme, SPECMON, for monitoring various parameters of a spectrometer, such as nitrogen pressure and sample temperature, and taking corrective action. The scheme is based on considerations of protection management which are of general application. Evaluation of the spectrometer state is incorporated in macros of the application software (VNMR) and is therefore very flexible. In contrast, corrective action is limited to the single one which is deemed fully safe: complete shutdown of the spectrometer and logging. Shutdown is implemented by a minor hardware modification of the spectrometer: the introduction of a second input to a relay already present for protection of the spectrometer power supply. Monitoring is handled by the host computer, and the shutdown command is transmitted via control lines of its series port, independent of the standard connection between the host computer and the NMR system console. The monitoring system (software and hardware) is unobtrusive in normal conditions, and it can be tested without affecting the operation of the spectrometer.

Left anterior descending artery length in left and right coronary artery dominance.

BACKGROUND: Coronary stenosis of the left anterior descending artery (LAD) is respected by cardiologists because of its negative influence on morbidity and mortality. An important anatomical consideration is the length of the LAD. OBJECTIVE: To investigate the relationship between length of LAD and coronary dominance. DESIGN: Retrospective comparison of 100 consecutive angiograms with left coronary dominance with 100 consecutive angiograms with right coronary dominance. The relationship between the length of the LAD and coronary dominance was analyzed. METHODS: We retrospectively compared 100 consecutive angiograms with left coronary dominance (the posterior descending artery being supplied by the circumflex artery) with 100 consecutive angiograms with right coronary dominance (the posterior descending artery being supplied by the right coronary artery). LADs were categorized into three types: type A, LAD terminating before the cardiac apex; type B, LAD reaching the apex but not supplying the inferoapical segment of the left ventricle; and type C, LAD wrapping around the apex and supplying the inferoapical segment. LAD typing was also analyzed in relation to gender. RESULTS: It was found that the LAD wrapped around the apex in 87% of cases of left coronary dominance but only in 47% of patients with right coronary dominance, and that the long LADs were more frequently seen in women than in men, irrespective of coronary dominance. CONCLUSIONS: We found that the LAD in left coronary dominance is usually long and wraps around the apex, and believe that angiographic interventions in such cases have important clinical significance.

Arthropod poisons and the cardiovascular system.

Animal poisons induce myocardial damage after envenomation. The cardiac manifestations after black widow spider bite are rarely observed and their prognostic significance are not known. Hymenoptera induce anaphylactic manifestations commonly observed in adults with previous coronary artery disease although myocardial involvement is observed in a few without previous heart disease. The mechanism of cardiac involvement after scorpion envenomation has been elucidated, however after widow spider bite or hymenoptera stings the mechanism of myocardial damage of those without previous heart disease is not clear.

The solution structure and internal motions of a fragment of the cytidine-rich strand of the human telomere.

We present the solution structure of d(CCCTA2CCCTA2CCCTA2CCCT), a fragment of the vertebrate telomere which folds intramolecularly. The four cytidine stretches form an i-motif which includes six intercalated C.C+ pairs and terminates with the cytidines at the 5' extremity of each stretch. Above, the second TA2 linker loops across one of the narrow grooves, while at the bottom, the first and third linkers loop across the wide grooves. At 30 degrees C, the spectra of the first and third linkers are quasi-degenerate. Severe broadening at lower temperature indicates that this results from motional averaging between at least two structures of each bottom loop, and makes it impossible to solve the configuration of the bottom loops directly, in contrast to the rest of the structure. We therefore turned to the modified sequence d(CCCTA(2)5MCCCTA2CCCUA2CCCT) in which the two base substitutions (underlined) break the quasi-symmetry between linkers 1 and 3. The three loops follow approximately the hairpin "second pattern" of Hilbers. In the first loop, T4 is in the syn orientation, whereas its analog in the third loop, U16, oriented anti, is in a central location, where it interacts with bases of both loops, thus contributing to their tight association. The only motion is a syn/anti flip of A18 in the third loop. Returning to the telomere fragment, we show that each of the bottom loops switches between the structures identified in the first and third loops of the modified structure. The motions are concerted, and the resulting configurations of the bottom loop cluster present a bulge to either right (T4 syn) or left (T16 syn).

The i-motif in nucleic acids.

Seven years after the discovery of the DNA i-motif, partial explanations for its occurrence have been uncovered, possibly involving CHellipsisO hydrogen bonds across the narrow grooves. Investigations of its biological significance have been encouraged by the demonstration and description of the intramolecular i-motif structure of human telomeric and centromeric sequences, by the recent observation of an intercalated RNA structure and by the discovery of proteins that associate with DNA sequences carrying cytosine repeats. The compatibility of the intercalation with peptide and phosphorothioate DNA analogs is favorable for possible pharmaceutical applications.

A unified theory of the B-Z transition of DNA in high and low concentrations of multivalent ions.

We showed recently that the high-salt transition of poly[d(G-C)]. poly[d(G-C)] between B-DNA and Z-DNA (at [NaCl] = 2.25 M or [MgCl(2)] = 0.7 M) can be ascribed to the lesser electrostatic free energy of the B form, due to better immersion of the phosphates in the solution. This property was incorporated in cylindrical DNA models that were analyzed by Poisson-Boltzmann theory. The results are insensitive to details of the models, and in fair agreement with experiment. In contrast, the Z form of the poly[d(G-m5C)] duplex is stabilized by very small concentrations of magnesium. We now show that this striking difference is accommodated quantitatively by the same electrostatic theory, without any adjustable parameter. The different responses to magnesium of the methylated and nonmethylated polymers do not come from stereospecific cation-DNA interactions: they stem from an experimentally derived, modest difference in the nonelectrostatic component of the free energy difference (or NFED) between the Z and B forms. The NFED is derived from circular DNA measurements. The differences between alkaline earth and transition metal ions are explained by weak coordination of the latter. The theory also explains the induction of the transition by micromolar concentrations of cobalt hexammine, again without specific binding or adjustable parameters. Hence, in the case of the B-Z transition as in others (e.g., the folding of tRNA and of ribozymes), the effect of multivalent cations on nucleic acid structure is mediated primarily by nonspecific ion-polyelectrolyte interactions. We propose this as a general rule for which convincing counter-examples are lacking.

Determination of the residence time of water molecules hydrating B'- DNA and B-DNA, by one-dimensional zero-enhancement nuclear Overhauser effect spectroscopy.

The residence time of water in the minor groove of the d(CGCGAATTCGCG) duplex has been determined by a recent measurement combining nuclear Overhauser enhancements (NOE, ROE) and 17O relaxation dispersion. The time is in the range of nanoseconds, so that it may be measured by a rather simple method proposed here, namely the choice of conditions such that the NOE between the observed DNA proton and a nearby water proton is zero. This condition is realized when the residence time of the water molecule is 0.178 times the nuclear magnetic resonance period (e.g. 0.297 ns at 600 MHz). It may be achieved by varying the magnetic field and/or the temperature. The zero-NOE measurement may be performed by one-dimensional NMR, and has therefore good sensitivity. We have developed excitation sequences which suppress two spurious contributions to the NOE: from neighboring exchangeable protons and from H3' protons whose chemical shift is close to that of water. The method is applied here to the comparison of residence times of water next to B-DNA and next to B'-DNA, the latter corresponding to better stacked, propeller-twisted base-pairs and a correspondingly narrower minor groove. In the minor groove of [d(CGCGAATTCGCG)]2, a B'-DNA duplex, the residence time of the water molecule next to H2 of adenine(6) (underlined), is 0.6 ns at 10 degreesC, in good agreement with the value obtained previously. The residence time is slightly but distinctly shorter for the water next to A5, suggesting non-cooperative departure of these two molecules which are presumed to be part of the hydration spine. Near A5 and A4 of [d(AAAAATTTTT)]2, another B'-DNA duplex, the residence times are approximately twice as long, but the activation enthalpies are about the same, ca. 38 kJ/mol. The residence time in the minor groove of the regular B-DNA sequence d(CGCGATCGCG) was 0.3 ns at 10 degreesC, shorter than in the case of the B'-DNA sequences by factors of 2 and 4, respectively. The temperature dependence is less, with an activation enthalpy of 27 kJ/mol. The major groove residence times are comparable for the three sequences, and a few times shorter than those of minor groove water. A value of 0.36 ns, or even more in case of rotation of water, is obtained around -8 degreesC. The most striking aspect of these results is the relatively small difference in the residence times of reputedly fast and slow-exchanging water molecules bound to DNA in biological conditions. This suggests that the spine of hydration is perhaps not a major stabilizer of the B'-DNA structure as compared with B-DNA.

Exaggerated blood pressure response at exercise in normotensive subjects: demographic and stress performance characteristics.

BACKGROUND: Exercise testing is an important diagnostic and prognostic procedure in the assessment of patients with hypertension. An exaggerated blood pressure response to exercise among normotensive subjects was found to be one of the best predictors of future hypertension. The demographic characteristics of patients with an exaggerated blood pressure response during exercise have not been adequately described. METHODS AND RESULTS: The demographic and stress performance characteristics of 2 groups of normotensive patients referred for exercise testing, one composed of patients with an exaggerated blood pressure response (group I, n=146) and a group of patients with a normal blood pressure response (group II, n=439) were prospectively compared. Patients in group I were older than those in group II (54+/-12 vs 51+/-13 years, P < .05). More men than women were found in both groups, yet significantly more in group I than in group II (83% vs 69% P < .001). Significantly more among the patients in group I had a higher level of education and were of Western origin than those in group II (P < .01). The resting systolic and diastolic blood pressures were higher in group I than in group II (131+/-18 vs 119+/-14 mm Hg, P< .001, and 81+/-8 vs 76+/-7 mm Hg, P < .001, respectively). The patients in group I achieved a higher percentage of the maximal predicted heart rate (88+/-7 vs 85+/-9 beats/min, P < .01). No significant differences were found between the groups in the duration of stress test and effort ischemia. CONCLUSIONS: Patients with a hypertensive blood pressure response during stress testing have specific demographic and exercise characteristics.

Patients with coronary collaterals and normal left ventricular systolic function: clinical, hemodynamic, and angiographic characteristics.

One hundred and twenty consecutive patients with significant coronary artery disease, normal left ventricular systolic function, and coronary collaterals were compared with 111 patients with the same characteristics but with no collaterals. No significant differences were found between the two groups in hypertension, diabetes mellitus, and smoking. The left ventricular end diastolic pressure was 16.4+/-7 in the study group and 16.9+/-6.9 in the controls (NS). Significantly more diseased vessels were observed in the study group than in the control group (2.1+/-0.6 versus 1.7+/-0.6, p=<0.001). One hundred and one totally occluded vessels were found in the study group but only two in the control group. The richest collateral supply was to the right coronary artery: 94 sources to 85 diseased vessels (111%) including 66 sources to 52 totally occluded arteries (127%); to the left anterior descending: 59 sources to 89 diseased vessels (66%) including 37 sources to 33 totally occluded arteries (112%). The poorest supply was to the left circumflex: 17 sources to 69 diseased vessels (25%), including nine sources to 16 totally occluded arteries (56%). No collaterals were observed in 14 totally occluded vessels in the study group and in two of the controls, while the systolic function at rest was still normal. It is suggested that coronary collaterals are important in preserving left ventricular systolic and diastolic performance at least at rest. Not readily visible collaterals may also prevent systolic dysfunction.

An intramolecular i-motif: the solution structure and base-pair opening kinetics of d(5mCCT3CCT3ACCT3CC).

We present a high-definition structure of d(5mCCT3CCT3ACCT3CC), a DNA sequence which resembles a four-times repeat of the C-rich strand of telomeres and centromeres. The structure is monomeric. The CC stretches form four hemi-protonated C.C base-pairs, belonging to two parallel-stranded duplexes which intercalate head-to-tail into an i-motif core. The four grooves of the core are similar to those observed previously in i-motif tetramers, with P-P distances around 0.9 nm and 1.4 nm for the narrow and wide grooves, respectively. At 0 degrees C, the structure is formed even at pH 7, despite the required protonation of cytidine pairs, suggesting that it may be biologically relevant.The intercalation topology of the i-motif core is read off the pattern of inter-residue cross-peaks along each groove: between H1' protons across the narrow grooves, and between amino and H2' protons across the wide grooves. In the hemi-protonated C.C pairs, the imino proton is shared equally between the two bases, as shown by the equal intensities of the NOESY cross-peaks between the imino proton and the two cis amino protons of the pair. Short inter-sugar distances and the direction of CH1' bonds are consistent with CH1'...O4' hydrogen bonds across the narrow grooves, as suggested by Berger et al. (1996). Proc. Natl. Acad. Sci. USA, 93, 12116-12121. At one extremity of the i-motif core, the T3A linker loops across one of the two wide grooves. It extends the core by stacking of A11, which also forms a strongly propeller-twisted reverse-Hoogsteen pair with T8. At the other extremity, the two T3 linkers loop side by side across the two narrow grooves, extending the core by stacking of a T5.T16 pair which connects the two linkers. In this T.T pair between parallel strands, the hydrogen bonds are from imino proton to O4, and the base-pair lifetime is 6 ms at 0 degrees C. The structures of segments 1 to 7 and 12 to 18, which form the i-motif core and the T3 loops, are related by a 2-fold pseudo-symmetry: the geometries and environment are so similar that the NOESY spectra are barely resolved. These various interactions illustrate how linker sequences may affect the stability, intercalation topology and folding pattern of the intramolecular i-motif.

Coronary collaterals in patients with normal and impaired left ventricular systolic function.

One hundred and twenty consecutive patients with significant coronary artery disease, normal left ventricular systolic function and coronary collaterals (group A) were compared to 120 patients with the same characteristics but with left ventricular systolic dysfunction (group B). No significant differences were found between the two groups on age, hypertension, diabetes mellitus and smoking. The left ventricular end diastolic pressure was 16+/-7 in group A, and 24+/-9 in group B (P<0.01). The number of diseased vessels was similar in both groups. More completely occluded vessels were found in group B (155 vs. 101 in group A). No significant difference was detected between the two groups in the distribution of the diseased vessels. In both groups, the richest collateral supply was to the right coronary artery, followed by collaterals to the left anterior descending. The poorest supply was to the left circumflex. In conclusion, patients with normal and abnormal left ventricular systolic function have similar coronary collateral characteristics.

[Angina pectoris and the severity of coronary artery stenosis].

The relationship between angina pectoris and the severity of coronary artery disease was evaluated in 146 patients with normal segmental and global, left ventricular, systolic performance. None had unstable angina or a previous myocardial infarction. A strong relationship was found between angina and the severity of coronary artery disease (p < 0.005). Significant, stable, angina pectoris as a clinical symptom indicated advanced coronary artery disease in this selected group of patients.

Exercise stress testing in a community clinic: experience with 38,970 patients.

BACKGROUND: Exercise testing is an important diagnostic and prognostic procedure in the assessment of patients with ischemic heart disease, arrhythmia and hypertension. OBJECTIVE: The purpose of this study was to determine the reasons for referral and the safety of exercise testing in the community. METHODS: The records of 38,970 patients who underwent stress testing in a community clinic were reviewed retrospectively. RESULTS: The majority of the tests (24,153) were performed by family physicians and the rest by cardiologists. The mean age of the patients was 54 +/- 12 years (range 12-81 years). Sixty-eight percent were males, and the majority were referred by family physicians (50%). The main reason for referral was chest pain evaluation (59%); none of the patients died during testing, two patients sustained myocardial infarction during the recovery period and ischemia was detected in 14% of patients. Persistent tachyarrythmia was observed in five patients (0.01%). A vasovagal reaction was observed during the recovery period in 36 patients (0.1%). CONCLUSION: This report emphasizes that stress tests can be performed safely in a community clinic with a very low rate of complications by family physicians or cardiologists.

A comparison of AMP degradation in the perfused rat heart during 2-deoxy-D-glucose perfusion and anoxia. Part I: The release of adenosine and inosine.

AMP degradation is studied in two models of the Langendorff-perfused rat heart which generate a large release of purines: the 2-deoxy-D-glucose (2DG)-perfused heart and the anoxic heart. In the 2DG model, mitochondrial energy generation is quasi-normal, despite a very low ATP concentration. Furthermore, inorganic phosphate (Pi) concentration is low, an important difference with anoxia where Pi is very high, up to 82 mM. Coronary release of purines is measured by high performance liquid chromatography, and myocardial metabolite content by 31P nuclear magnetic resonance spectroscopy. In the 2DG-perfused hearts with glucose or acetate, the purine release consists nearly exclusively of inosine [up to 130 nmol/(min x gww)] while adenosine is less than 1 nmol/(min x gww). A possible interpretation is that AMP degradation proceeds mainly through deamination to inosine monophosphate by AMP deaminase (the IMP pathway). In contrast, the purine release in anoxia (100% N2) contains comparable quantities of adenosine and inosine [respectively 30 and 20 nmol/(min x gww)], indicating that part of AMP is dephosphorylated directly to adenosine. Comparison with the 2DG model suggests that the release of adenosine in the anoxic heart is a result of inhibition of AMP deaminase by Pi.

AMP degradation in the perfused rat heart during 2-deoxy-D-glucose perfusion and anoxia. Part II: The determination of the degradation pathways using an adenosine deaminase inhibitor.

Using the adenosine deaminase inhibitor erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA), we determine the contribution of the adenosine pathway to the abundant purine release of two Langendroff-perfused rat heart models which differ particularly in inorganic phosphate (Pi) content: the 2-deoxy-D-glucose (2DG) perfused heart and the anoxic heart. We measure the release of coronary purines by high performance liquid chromatography, and the content of myocardial metabolites by 31P nuclear magnetic resonance spectroscopy. In the 2DG-perfused heart (2 mM for 45 min), the release of inosine [130 nmol/(min.gww)] is much larger than that of adenosine, and EHNA (50 microM) has little effect, showing that the pathway of inosine monophosphate (IMP) accounts for 97% of purine catabolism. In the anoxic heart (100% N2 for 45 min), where inosine and adenosine release are comparable in the absence of EHNA, the inhibitor reduces the release of inosine and catabolites from 50 to 20 nmol/(min.gww) and increases that of adenosine [from 30 to 55 nmol/(min.gww)], showing that the contributions of the IMP and adenosine pathways are 23 and 77%. The difference between the two models has been ascribed to the inhibition of AMP deaminase by Pi in the anoxic heart (Chen W, et al., 1996). We discuss the physiological significance of this heart-specific duality of degradation pathways.

Interleukin-6 release following scorpion sting in children.

Interleukin-6 levels were measured in the serum of ten children following severe scorpion envenomation. Measurements were taken on arrival, at the emergency room, and 12 and 24 hr after arrival. Interleukin-6 was markedly elevated in the serum of eight out of ten children on arrival. Interleukin-6 levels gradually decreased toward normal values on 12 and 24 hr measurements, but remained above control levels on all measurements. These results imply that signs and symptoms following scorpion envenomation may in part be explained by release of cytokines. Human and experimental animal studies are required in order to verify the assumption that interleukin-6 and other cytokines are involved in the pathogenesis of scorpion envenomation.

Acid-induced exchange of the imino proton in G.C pairs.

Acid-induced catalysis of imino proton exchange in G.C pairs of DNA duplexes is surprisingly fast, being nearly as fast as for the isolated nucleoside, despite base-pair dissociation constants in the range of 10(-5) at neutral or basic pH. It is also observed in terminal G.C pairs of duplexes and in base pairs of drug-DNA complexes. We have measured imino proton exchange in deoxyguanosine and in the duplex (ATATAGATCTATAT) as a function of pH. We show that acid-induced exchange can be assigned to proton transfer from N7-protonated guanosine to cytidine in the open state of the pair. This is faster than transfer from neutral guanosine (the process of intrinsic catalysis previously characterized at neutral ph) due to the lower imino proton pK of the protonated form, 7.2 instead of 9.4. Other interpretations are excluded by a study of exchange catalysis by formiate and cytidine as exchange catalysts. The cross-over pH between the regimes of pH-independent and acid-induced exchange rates is more basic in the case of base pairs than in the mononucleoside, suggestive of an increase by one to two decades in the dissociation constant of the base pair upon N7 protonation of G. Acid-induced catalysis is much weaker in A.T base pairs, as expected in view of the low pK for protonation of thymidine.