Aggregation of Markov flows I: theory

A Markov flow is a stationary measure, with the associated flows and mean first passage times, for a continuous-time regular jump homogeneous semi-Markov process on a discrete state space. Nodes in the state space can be eliminated to produce a smaller Markov flow which is a factor of the original one. Some improvements to the elimination methods of Wales are given. The main contribution of the paper is to present an alternative, namely a method to aggregate groups of nodes to produce a factor. The method can be iterated to make hierarchical aggregation schemes. The potential benefits are efficient computation, including recomputation to take into account local changes, and insights into the macroscopic behaviour.This article is part of the theme issue 'Hilbert's sixth problem'.

Disposition of [s]-heparin in the rat

[(35)S]-Heparin is rapidly taken up by tissues after intraperitoneal injection andrapidly degraded. Skin, aorta and lung showed an especially high affinity for[(35)S]-heparin. In these organs, as well as in adrenal gland, stomach, heart and brain,the isotope was found preponderantly as dialysable metabolite(s) of heparin. Another group of tissues (large intestine, fat, kidney and liver) was characterized by a smaller proportion of dialysable material. Tissues that showed a high affinity for exogenous heparin appeared to catabolize it rapidly. It is also noted that some of the radioactive material present in tissues after the injection of [(35)S]-heparin could come from the uptake of [(35)S]-sulphate resulting from the degradation of [(35)S]-heparin. The incorporation of [(35)S]-sulphate into the sulphomucopolysaccharides of some tissues is recorded.

Blood levels of flupenthixol in patients with acute and chronic schizophrenia

Plasma levels of flupenthixol were estimated by three methods in 30 patients with acute schizophrenia and 29 patients with chronic schizophrenia. These levels were related to clinical response, anterior pituitary hormone secretion, platelet monoamine oxidase activity, the effects of the concurrent administration of anticholinergic drugs, and body weight. No clearcut relationships between plasma flupenthixol levels and any of these variables were demonstrated. The practical clinical value of the estimation of plasma flupenthixol is limited at the present time.

The DRD2 TaqI-B polymorphism and its relationship to smoking abstinence and withdrawal symptoms

The dopamine receptor D2 (DRD2) gene has polymorphisms that have been linked to regulation of the dopamine system and to an increased prevalence of smoking. The present study examined the relationship of the DRD2 TaqI-A and -B polymorphisms with short-term clinical outcome (abstinence and withdrawal symptoms), collected from daily (14 pre-quit and 42 post-quit) diary data among smokers (n=116) treated with the nicotine patch plus either venlafaxine or placebo. The results showed that B1/B1 or B1/B2 smokers were slightly less likely to be abstinent on a given day than those homozygous for the TaqI-B2 allele. Significant DRD2 TaqI-B x time interactions were found for several of the withdrawal scales, indicating that those smokers with the B1/B1 or B1/B2 genotypes tended to report more symptoms over time compared to those with the B2/B2 genotype. No interactions or main effects were found for the DRD2 TaqI-A polymorphism. The findings demonstrate that smokers homozygous for the TaqI-B2 allele experience progressive improvement in self-reported withdrawal symptoms while smokers with the TaqI-B1 allele showing little change.

Healthcare providers' sun-protection promotion and at-risk clients' skin-cancer-prevention outcomes

BACKGROUND

This study aims to determine whether healthcare providers' (HCPs') communication dealing with sun-protection (i.e., counseling) is associated with clients' skin-cancer-related prevention practices, detection self-efficacy, and knowledge.

METHODS

Secondary analysis of two surveys of 1,469 randomly sampled farmers and soccer participants from southeast and coastal Georgia.

RESULTS

Farmers and soccer participants who report ever having been counseled by a HCP about how to protect their skin from the sun report being more likely to wear sunscreen (P < 0.05), get clinical exams of their skin (P < 0.001), be certain that they can recognize unhealthy changes in their skin (P < 0.001), be certain that they know how to perform a skin exam (P < 0.001), and be knowledgeable about skin cancer prevention (P < 0.05 and P < 0.001, respectively); soccer participants are additionally more likely to wear protective headgear (P < 0.05) and perform monthly self-exams of their skin (P < 0.001). All analyses incorporated three control variables: participants' prior history of skin cancer, age, and non-HCP-derived skin-cancer awareness.

CONCLUSIONS

Findings suggest that HCPs' counseling can positively shape skin-cancer-related prevention practices, detection self-efficacy, and knowledge. Additional research is needed on HCPs' actual communication about skin cancer and sun protection and its influence on client outcomes.

Closing medical encounters: two physician practices and their implications for the expression of patients' unstated concerns

When patients visit primary-care physicians, they frequently have more than one concern. Patients' first concerns are solicited by physicians at the beginnings of encounters. A challenge to health care is how to get patients' additional concerns raised as topics of discussion. If patients' additional concerns are addressed, it tends to occur at the end of encounters. Using the methodology of conversation analysis, this article identifies and describes the interactional organization of two physician-initiated communication practices that are used to negotiate the closure of the business of encounters and a transition into the activity of closing encounters themselves. These practices have different implications for the topicalization of patients' additional concerns.

The time course of emotional and attentional modulation of the startle eyeblink reflex during imagery

Two studies were conducted to examine the time course of attentional and emotional processing using the startle eyeblink reflex. Forty-eight participants listened to a series of 1500-ms tones that occurred every 6 s. The tones signaled participants to generate emotional images that were positive or negative in valence and high or low in arousal. Auditory startle probes occurred 120 ms, 1400 ms, or 4000 ms after tone onset. Startle inhibition was seen 120 ms after tone onset and startle facilitation was found at 1400 ms, compared to startles elicited 4000 ms after tone onset. Startle inhibition was greater at 120 ms when the tone signaled imagery, indicating an attentional effect. A second experiment found that this effect was not caused by the comparative rarity of the tones signaling imagery. Startle magnitude was also smaller at 1400 ms when the tone signaled imagery compared to no-imagery tones. The type of imagery did not modulate the startle response 120 ms after tone onset, but negative valence imagery enhanced startle magnitude at 1400 ms and 4000 ms after tone onset, and high arousal also enhanced startle magnitude at 4000 ms. Thus, attention and emotion followed different time courses in affecting the startle reflex response during imagery.

Women's health problems in soap operas: a content analysis

A content analysis of women's health problems in network daytime serials is reported. Results indicate a preponderance of such problems as substance abuse, falls resulting in death or injury, comas or unconsciousness, mental health concerns (most notably represented by amnesia and multiple personality), concerns about AIDS, automobile accidents, being drugged, fainting, pregnancy problems, and violent acts resulting in harm. Such concerns as breast and cervical cancer and heart disease are less frequently portrayed.

Experimental Characterization of the Higher Vibrationally Excited States of HCO(+): Determination of omega(2), x(22), g(22), and B(030)

Analyses of high Rydberg series of HCO converging to the (030) vibrational state of the cation establish rovibrational state-detailed thresholds for HCO(+). UV-visible laser double resonance isolates series for assignment. Strongly vertical Rydberg-Rydberg transitions from photoselected N' = 0 and N' = 2 rotational levels of the Sigma(-) Renner-Teller vibronic component of the 3ppi (2)Pi (030) complex define individual series converging to rotational levels, N(+) = 1 through 5 and 3 through 5 of the HCO(+) vibrational states (03(1)0) and (03(3)0), respectively. Extrapolation of autoionizing series locates the positions of these rovibrational states to within +/-0.01 cm(-1). The use of this information combined with precise ionization limits for lower vibrational states determined from earlier Rydberg extrapolations and spectroscopic information available from infrared absorption measurements enables an estimate of the force-field parameters for HCO(+) bending. These parameters include the harmonic bending frequency, omega(2) = 842.57 cm(-1), the vibrational angular momentum splitting constant, g(22) = 3.26 cm(-1), and the diagonal bending anharmonicity, x(22) = -2.53 cm(-1), separated from the off-diagonal contribution, x(12), by reference to ab initio calculations. Results of experiment on the higher vibrationally excited states of HCO(+) are compared with recent theoretical predictions. Copyright 2000 Academic Press.

Transient kinetics of substrate binding to Na+/K(+)-ATPase measured by fluorescence quenching

This paper examines the transient kinetics of substrate binding to the Na+/K(+)-ATPase labelled with iodoacetamidofluorescein (IAF) using fluorescence quenching by trinitrophenyl-ATP (TNP-ATP). Earlier work (E.H. Hellen, P.R. Pratap, 1996, Fluorescence quenching of IAF-Na+/K(+)-ATPase via energy transfer to TNP-labelled nucleotide, Proceedings of the VIIIth International Conference on the Na+/K(+)-ATPase, in press) has shown that TNP-nucleotide binds to specific sites (from which unlabelled nucleotide can displace it) and nonspecific sites (from which unlabelled nucleotide cannot displace it). Under stopped-flow conditions, quenching of IAF-enzyme fluorescence was well described by a stretched exponential (F(t) = F infinity + delta F exp[-Bt alpha]). Physically, this function may be interpreted in terms of its inverse Laplace transform phi (k), which describes a distribution of rate-constants; alpha reflects the width of this distribution. As TNP-ATP concentration increased, alpha decreased, reflecting TNP-ATP binding to sites with higher energy barriers. alpha decreased by about the same amount with increasing [TNP-ATP] in the presence of saturating ATP, indicating that the distribution of rate-constants is largely associated with the nonspecific binding sites. However, alpha was significantly less than 1 for ATP-induced fluorescence recovery in the presence of TNP-ATP, indicating that rate-constants associated with specific binding site are also distributed. The distribution of rate-constants for binding to the specific site indicates a distribution in the energy of the transition state for substrate binding. These results suggest that the specific binding site (in either the empty or the full state) may exist in a series of conformations separated by small energy barriers. However, the energy barriers for binding associated with these conformations are significantly distributed.

Iodine insufficiency and neonatal hyperthyrotropinaemia in Hong Kong

OBJECTIVES

23% of the neonatal hypothyroidism in Hong Kong is transient. The present study aims to evaluate iodine excretion in healthy pregnant women in Hong Kong and to determine whether iodine insufficiency may occur in the local population to account for the type of neonatal thyroid dysfunction seen in our screening programme.

SUBJECTS

Pilot screening of urinary iodine excretion was determined in 253 healthy pregnant women between 32 and 36 weeks gestation. Fetal and maternal thyroid function in relation to urinary iodine excretion was evaluated in another 55 pregnant women who had given birth to infants with cord blood TSH > or = 16 mIU/I (95th percentile of the cord blood TSH screening programme) and the results were compared to a control group of 160 healthy women whose infants had cord blood TSH < 16 mIU/I.

RESULTS

Using a cut-off value of 0.79 mumol/l, a level as defined by WHO as iodine deficiency, we found that 35.8% of the pregnant women had urinary iodine concentrations below this cut off value. We demonstrated that the existence of borderline iodine supply affected the maternal and fetal thyroid function as evidenced by (i) a negative correlation between maternal TSH and urinary iodine concentration, (ii) higher cord blood TSH in those infants whose mothers had a low urinary iodine concentration as compared to those in whose mothers it was normal, (iii) women who had given birth to infants with cord blood TSH > or = 16 mIU/I had lower urinary iodine concentrations and serum fT4 levels as compared to mothers who had given birth to infants with normal cord TSH levels, and their offspring also had higher cord blood thyroglobulin levels.

CONCLUSION

Although Hong Kong is not a goitrous area, borderline iodine deficiency exists. Iodization of salt in our community could obviate the necessity for iodine supplements in pregnant women and other at-risk groups.

Kinetics of conformational changes associated with potassium binding to and release from Na+/K(+)-ATPase

The Na+/K(+)-ATPase functions in cells to couple energy from the hydrolysis of ATP to the transport Na+ out and K+ in. The fluorescent probe IAF (iodoacetamidofluorescein) covalently binds to this enzyme, reporting conformational changes without inhibiting enzyme activity. This paper describes experiments using dog kidney enzyme labeled with IAF to examine kinetics of conformational changes resulting from added Na+ and K+, measured in terms of steady-state and stopped-flow fluorescence changes. Kinetics of these fluorescence changes were examined as a function of temperature from two initial conditions: (a) enzyme in the high-fluorescence form (E(high)) was rapidly mixed with varying [K+]; and (b) enzyme in the low-fluorescence form (E(low)) was rapidly mixed with varying [ATP]. These experiments showed: (1) The rate constant for the fluorescence change from E(high) to E(low) was much larger than that for the opposite transition, E(low) to E(high); (2) the apparent free energy of activation (Ea(app)) for the two transitions were different (as estimated from Arrhenius plots); (3) under steady-state conditions, IAF fluorescence did not change when ATP was added to E(low)(K+) in the absence of Na+; (4) the apparent free energy of activation was independent of [K+] for the E(high) to E(low) transition (at 16.4 kcal/mol) but increased with [ATP] for the E(low) to E(high) transition; (5) Ea(app) for the E(low) to E(high) transition with 1 mM ATP was approximately the same as that in the absence of ATP (34 kcal/mol). These results can be interpreted as: (i) in the transition from E(low) to E(high), IAF reported a conformational change that occurred after K+ release to the intracellular side and which is involved in Na+ binding; (ii) Ea(app) increased with [ATP], while increasing the entropy of the transition state. Thus, ATP appeared to destabilize the enzyme during the transition from E(low) to E(high).

Existence of iodine deficiency in Hong Kong--a coastal city in southern China

OBJECTIVE

Iodine deficiency is a serious public health problem worldwide which is associated with mental retardation and cretinism. In view of a high incidence of transient neonatal hypothyroidism and a relatively high mean cord blood thyrotropin (TSH) concentration, a pilot study was carried out to analyse the urine iodine excretion in Hong Kong, a coastal city in the southern part of China.

DESIGN

Early morning urine was collected from healthy volunteers including children (n = 104), adults (n = 112) and elderly subjects (n = 349). A semi-quantitative questionnaire survey on the pattern of food intake was conducted in the adults and elderly.

RESULTS

45.3% of the children, 51.7% of the adults and 55.3% of the elderly had urine iodine concentration below the criteria for iodine sufficiency (< 0.79 mumol/l). Iodine content in the drinking water and salt was low. A dietary survey revealed that seafood was not commonly consumed. 50-80% of the subjects never consumed high-iodine containing food such as seaweed, kelp or laver, and only 50% consumed seawater fish daily.

CONCLUSION

We confirmed that although Hong Kong is a non-goitrous area, iodine insufficiency exists. It is unsafe to assume that iodine deficiency does not exist in coastal urban areas.

The Howard University Hospital Transplant and Dialysis Support Group: twenty years and going strong

This article discusses group therapy as part of a multidisciplinary approach to the management of the various psychological and physical rehabilitation concerns posed by kidney and liver transplant candidates and recipients at Howard University Hospital in Washington, DC. The group's history, format, intervention foci, and roles of clinicians and patients attending the group are described and evaluated. Given the relative paucity of research literature in this area, the authors offer recommendations for empirical evaluation of the benefits of multidisciplinary group psychotherapy in ameliorating physical and emotional suffering and prolonging life among transplant patients.

Rapid kinetic analyses of the Na+/K(+)-ATPase distinguish among different criteria for conformational change

The Na+/K(+)-ATPase couples the hydrolysis of ATP to the transport of Na+ and K+ via a phosphorylated intermediate and conformational changes. In order to identify these conformational changes, we have probed the sequence of steps from EP(3Na+ in) to EP + 3Na+ out with three fluorescent probes (IAF: 5-iodoacetamidofluorescein; BIPM: N-[p-(2-benzimidazolyl)phenyl]maleimide; and RH421) and the sensitivity of their fluorescence change to oligomycin and divalent cations (Ca2+ and Mn2+). The magnitude (% delta F) and rate constant (k(obs)) of ATP-induced fluorescence changes were measured on a fluorescence stopped-flow apparatus, and yielded the following results. (a) With RH421, k(obs) and % delta F varied with [Na+] (maximal k(obs) = 100 s-1, K1/2 = 6 mM; % delta Fmax = 6%, K1/2 = 1 mM); these values are comparable to those previously reported using IAF-labeled enzyme (Pratap, P.R., Robinson, J.D. and Steinberg, M.I. (1991) Biochim. Biophys. Acta 1069, 288-298). (b) With BIPM-labeled enzyme k(obs) did not vary with [Na+] over the range tested, and was twice as high as the maximum k(obs) for RH421. (c) Treatment with oligomycin reduced k(obs) for all three probes to about the same level (approximately 1-2 s-1) while % delta Fmax was largely unaffected. (d) Replacing Mg2+ with Ca2+ had similar effects to treatment with oligomycin. (e) RH421 fluorescence change was completely abolished in the presence of oligomycin and Ca2+. (f) Replacing Mg2+ with Mn2+ decreased IAF fluorescence, i.e., put the enzyme in an E2-like form, reduced k(obs), and rendered oligomycin less effective in reducing k(obs). From these results, we conclude: (a) the release of the second/third Na+ is the rate-limiting step for the conformational change measured by IAF and charge transfer measured with RH421; (b) BIPM indicates an earlier step, either the deocclusion of Na+ and/or the release of the first Na+; (c) oligomycin blocks Na+ deocclusion, and this step is sensitive to the divalent cation used to activate enzyme phosphorylation; and (d) Ca2+ slows the step reported by IAF as well. These experiments indicate that a simple model with two conformations (E1 and E2) is insufficient to explain transient kinetic data.

Improved mammography with a reduced radiation dose

A 2-cm-high focused air-interspaced grid with a 7:1 ratio and eight lamellae per inch was devised. The grid is arc-shaped and pivots on its focal point, the anode-cathode axis. Milliamperage was 35% less for breast phantom radiographs obtained with the new grid versus those obtained with a conventional 5:1 mammographic grid. In a comparison study of five mammograms, each evaluated for five parameters, the images obtained with the new grid were judged to be of equal or better quality than those obtained with a conventional grid in 17 of 20 comparisons.

The requirement of low calcium dialysate in patients on continuous ambulatory peritoneal dialysis receiving calcium carbonate as a phosphate binder

In the present study we investigated the requirement of low calcium dialysate in 35 patients on continuous ambulatory peritoneal dialysis (CAPD) receiving calcium carbonate as the sole phosphate binder over a 12-month period. Patients with corrected serum calcium > or = 2.85 mmol/L after switching to oral calcium carbonate were given 1 to 3 2-litre exchanges of 2.5 mEq/L calcium dialysate. Serum phosphate level dropped from the pretreatment value of 2.95 +/- 0.62 to a level of between 1.70 +/- 0.41 to 2.03 +/- 0.44 mmol/L 2 weeks after therapy. Corrected serum calcium level increased significantly from 2 weeks onwards. Serum alkaline phosphatase rose initially at 2 and 6 weeks and decreased from 3 months onwards. Serum parathyroid hormone level dropped significantly from a mean pretreatment level of 569 to 320 pg/ml after 12 months (p < 0.001). Serum aluminum decreased significantly from a mean of 1.04 to 0.65 umol/L (p < 0.01). Daily calcium carbonate requirement fluctuated but tended to increase till 8 months and plateaued and ranged from 2.61 +/- 0.57 to 3.98 +/- 2.11 gm. The daily requirement of low calcium dialysate followed a similar trend with approximately three-quarters of patients ultimately requiring at least 1 bag of low calcium dialysate. Eight patients did not require low calcium dialysate. Patients who required low calcium dialysate were significantly older, had a significantly lower pretreatment serum parathyroid hormone and higher serum aluminum levels than those who did not.(ABSTRACT TRUNCATED AT 250 WORDS)

Lovastatin in glomerulonephritis patients with hyperlipidaemia and heavy proteinuria

Lovastatin, a 3-hydroxy-3-methylglutaryl coenzyme A inhibitor, was given to 14 patients with unremittent nephrotic syndrome (heavy proteinuria with hyperlipidaemia) for 6 months. Treatment was started at an initial dose of 20 mg/day, increasing to a maximum of 80 mg/day. Treatment was well tolerated except in two patients: one developed rhabdomyolysis and one severe hypertriglyceridaemia requiring an additional antihyperlipidaemic agent. Lovastatin was effective in reducing serum cholesterol, LDL-C and apolipoprotein B in the remaining 12 patients. Cholesterol was reduced by 31% from 8.24 +/- 0.49 mmol/l (mean +/- SEM) to 5.7 +/- 0.18 mmol/l after 6 months (P less than 0.001). LDL-C was normalized to 3.26 +/- 0.21 mmol/l from a pretreatment value of 5.76 +/- 0.48 mmol/l (P less than 0.001), a decrease of 43%. Serum apolipoprotein B was also normalized to 1.11 +/- 0.09 g/l from a basal level of 1.51 +/- 0.10 g/l (P less than 0.05). Triglyceride, HDL-C and apolipoprotein A1 concentrations were unchanged. Proteinuria as well as renal albumin clearance were unchanged. GFR by plasma radioisotope Cr-EDTA clearance for the whole group was unaltered by treatment. However, among those with relatively good pretreatment renal function (GFR greater than 70 ml/min per 1.73 m2), GFR increased at the end of 6 months' treatment (118.2 +/- 15 ml/min per 1.73 m2 versus 77.6 +/- 8.4 ml/min per 1.73 m2 in wash-out phase).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of choline on Na(+)- and K(+)-interactions with the Na+/K(+)-ATPase

Choline chloride, 100 mM, stimulates Na+/K(+)-ATPase activity of a purified dog kidney enzyme preparation when Na+ is suboptimal (9 mM Na+ and 10 mM K+) and inhibits when K+ is suboptimal (90 mM Na+ and 1 mM K+), but has a negligible effect at optimal concentrations of both (90 mM Na+ and 10 mM K+). Stimulation occurs at low Na+ to K+ ratios, but not at those same ratios when the actual Na+ concentration is high (90 mM). Stimulation decreases or disappears when incubation pH or temperature is increased or when Li+ is substituted for K+ or Rb+. Choline+ also reduces the Km for MgATP at the low ratio of Na+ to K+ but not at the optimal ratio. In the absence of K+, however, choline+ does not stimulate at low Na+ concentrations: either in the Na(+)-ATPase reaction or in the E1 to E2P conformational transition. Together, these observations indicate that choline+ accelerates the rate-limiting step in the Na+/K(+)-ATPase reaction cycle, K(+)-deocclusion; consequently, optimal Na+ concentrations reflect Na+ accelerating that step also. Thus, the observed K0.5 for Na+ includes high-affinity activation of enzyme phosphorylation and low-affinity acceleration of K(+)-deocclusion. Inhibition of Na+/K(+)-ATPase and K(+)-nitrophenylphosphatase reactions by choline+ increases as the K(+)-concentration is decreased; the competition between choline+ and K+ may represent a similar antagonism between conformations selected by choline+ and by K+.

The reaction sequence of the Na+/K(+)-ATPase: rapid kinetic measurements distinguish between alternative schemes

Conformational changes between E1 and E2 enzyme forms of a dog kidney Na+/K(+)-ATPase preparation labeled with 5-iodoacetamidofluorescein were followed with a stopped-flow fluorimeter, in terms of the rate constant, kobs, and the steady-state magnitude, % delta F of fluorescence change. On rapid mixing of enzyme plus Mg2+ plus Na+ with saturating (0.5 mM) ATP in the absence of K+, kobs varied with Na+ concentration in the range 0-155 mM, with a K1/2 of 10 mM, while % delta F was relatively insensitive to Na+, with a K1/2 of 0.5 mM. Oligomycin reduced kobs by 98-99% for Na+ greater than or equal to 10 mM, but only by 50% for Na+ = 1 mM; % delta F was reduced at most by 20%. At 155 mM Na+, both kobs and % delta F changed if K+ was present with the enzyme. kobs decreased by 50% when K+ was increased from 0 to 0.2 mM, but increased when K+ was varied in the range 0.2-5 mM. K+ increased % delta F by a factor of 3 with a K1/2 of 0.3-0.5 mM as measured in both stopped-flow and steady-state experiments. These data are considered in terms of the derived presteady-state equations for two alternate schemes for the enzyme, with the E1P to E2P conformational change either preceding (Albers-Post) or following (Nørby-Yoda-Skou) Na+ transport and release. The analysis indicates that: (i) Na+ must be released before the conformational transition, from an E1 form; (ii) the step in which the second and/or third Na+ is released is rate-limiting, but this release is accelerated by Na+; and (iii) the release is also accelerated by K+ acting with low affinity (possibly at extracellular sites).

Na+/K(+)-ATPase: modes of inhibition by Mg2+

Adding 15 mM free Mg2+ decreased Vmax of the Na+/K(+)-ATPase reaction. Mg2+ also decreased the K0.5 for K+ activation, as a mixed inhibitor, but the increased inhibition at higher K+ concentrations diminished as the Na+ concentration was raised. Inhibition was greater with Rb+ but less with Li+ when these cations substituted for K+ at pH 7.5, while at pH 8.5 inhibition was generally less and essentially the same with all three cations: implying an association between inhibition and ion occlusion. On the other hand, Mg2+ increased the K0.5 for Na(+)-activation of the Na+/K(+)-ATPase and Na(+)-ATPase reactions, as a mixed inhibitor. Changing incubation pH or temperature, or adding dimethylsulfoxide affected inhibition by Mg2+ and K0.5 for Na+ diversely. Presteady-state kinetic studies on enzyme phosphorylation, however, showed competition between Mg2+ and Na+. In the K(+)-phosphatase reaction catalyzed by this enzyme Mg2+ was a (near) competitor toward K+. Adding Na+ with K+ inhibited phosphatase activity, but under these conditions 15 mM Mg2+ stimulated rather than inhibited; still higher Mg2+ concentrations then inhibited with K+ plus Na+. Similar stimulation and inhibition occurred when Mn2+ was substituted for Mg2+, although the concentrations required were an order of magnitude less. In all these experiments no ionic substitutions were made to maintain ionic strength, since alternative cations, such as choline, produced various specific effects themselves. Kinetic analyses, in terms of product inhibition by Mg2+, require Mg2+ release at multiple steps. The data are accommodated by a scheme for the Na+/K(+)-ATPase with three alternative points for release: before MgATP binding, before K+ release and before Na+ binding. The latter alternatives necessitate two Mg2+ ions bound simultaneously to the enzyme, presumably to divalent cation-sites associated with the phosphate and the nucleotide domains of the active site.

Effect of phosphatidylcholine on ultrafiltration in patients on continuous ambulatory peritoneal dialysis

Oral phosphatidylcholine at 900 mg/day was given to 4 patients with high lymph absorption for 8 weeks. Fluid and solute transfer before and after treatment were compared to 4 similar controls given placebo. None of the patients had overt ultrafiltration problems. After treatment, overnight peritoneal effluent phospholipid content did not change significantly. Ultrafiltration as well as solute and glucose transfer remained unchanged at the end of 8 weeks. A controlled trial on patients with overt ultrafiltration problems for a longer duration is required to further elucidate the role of phosphatidylcholine supplementation in patients on continuous ambulatory peritoneal dialysis.

A stepless needle-dilator for expedient percutaneous catheterization: technical note

A new stepless needle-dilator is described which allows arterial puncture and dilation in a single step using a single wall puncture technique. The new needle-dilator causes significantly less arterial damage than a conventional dilator (p less than 0.05). Additionally, time and cost savings are realized by clinical users.

Interventional magnetic resonance imaging in the head and neck

Interventional MRI is clearly in its early stages of development. While the value of MR-guided aspiration cytology and MR evaluation of deep electrode implantation in the brain has already been confirmed with human clinical studies, the future of MR-guided interstitial laser therapy remains to be proven. Despite this, as we look ahead into the 1990s and the millennium, it is possible to imagine dedicated MR laser therapy units for combined radiological and surgical outpatient approaches in what may become the operating rooms of the 21st century.

Interstitial laser phototherapy assisted by magnetic resonance imaging: a new technique for monitoring laser-tissue interaction

The rapid technological advances of magnetic resonance imaging, laser fiberoptics, and compatible probes may allow treatment of deep and sometimes surgically unreachable tumors of the head and neck with minimal morbidity through interstitial laser phototherapy. In this study, a new application of magnetic resonance imaging was developed to monitor and quantify laser-induced tissue damages. Pig skin was exposed to increased levels of argon laser (514.5 nm) at energy densities between 62.5 and 375 J/cm2 as determined by an accurate and reproducible method of dosimetry. Thermal profiles were recorded using an infrared sensor and T1- and T2-weighted magnetic resonance images were taken; afterward, biopsies were performed to quantitate the level of tissue damage. Our results demonstrate that above a certain threshold of laser energy, the magnetic resonance imaging findings are temperature dependent. Appropriate development of a scale matching laser energies, temperature profiles, T1- and T2-weighted magnetic resonance images, and histological quantitation of tissue destruction will allow us to optimize the three-dimensional control and monitoring of laser-tissue interactions.

Differential effects of substrates on three transport modes of the Na+/K(+)-ATPase

With a purified Na+/K(+)-ATPase preparation reconstituted into phospholipid vesicles, Na+/K+, Na+/Na+, and uncoupled Na+ transport were studied using three nucleotides and five substrates of the K(+)-phosphatase reaction that this enzyme also catalyzes. For Na+/K+ exchange, CTP was half as effective as ATP and GTP one-twentieth; of the phosphatase substrates only carbamyl phosphate and 3-O-methylfluorescein phosphate produced significant transport and at merely 1% of the rate with ATP. For Na+/Na+ exchange, comparable rates of transport were produced by ATP, CTP, carbamyl phosphate and acetyl phosphate, although the actual rate of transport with ATP was only 2.4% of that for Na+/K+ exchange; slower rates occurred with GTP (69%), 3-O-methylfluorescein phosphate (51%), and nitrophenyl phosphate (33%). Only umbelliferone phosphate was ineffective. For uncoupled Na+ transport results similar to those for Na+/Na+ exchange were obtained, but the actual rate of transport was still slower, 1.4% of that for Na+/K+ exchange. Thus, not only nucleotides but a variety of phosphatase substrates (which are phosphoric acid mixed anhydrides) can phosphorylate the enzyme at the high-affinity substrate site to form the E1P intermediate of the reaction sequence. Oligomycin inhibited Na+/K+ exchange with ATP by half, but with carbamyl phosphate not at all; with CTP the inhibition was intermediate, one-fourth. By contrast, oligomycin inhibited Na+/Na+ exchange by one-fifth with all three substrates. A quantitative, steady-state kinetic model accounts for the relative magnitudes of Na+/K+ and Na+/Na+ exchanges with ATP, CTP, and carbamyl phosphate as substrates, as well as the extents of inhibition by oligomycin. The model requires that even when Na+ substitutes for K+ a slow step in the reaction sequence is the E2 to E1 conformational transition.

The biocompatibility of compressed collagen foam plugs

The tissue reaction to reexpanded, purified bovine collagen sponge placed percutaneously into the lung, pleural space, liver, kidney, and muscle was studied in dogs and rabbits. In addition, the biocompatibility and radiopacity of tantalum-treated collagen foam plugs was examined. No adverse effects were found. We believe that collagen plugs may be of use in occluding needle tracts from biopsy sites to prevent complications such as bleeding or pneumothoraces.

Pharmacokinetics of amikacin in critically ill neonatal foals treated for presumed or confirmed sepsis

Fourteen foals less than four days of age were treated with the aminoglycoside, amikacin sulphate, and either penicillin or ampicillin for septicaemia, pneumonia, and/or failure of passive immunoglobulin transfer. Serum amikacin concentrations were determined at three times during an 8 or 12 h dosing interval. A 7.0 mg/kg bodyweight dose of amikacin every 8 h was appropriate. Prematurity did not influence mortality. All seven premature foals survived, whereas four of the seven full term foals died. Uraemia in three foals was caused by urinary bladder rupture; amikacin-induced nephrotoxicity was not recognised by clinical chemistries (elevations in serum creatinine or blood urea nitrogen concentrations) or post-mortem findings.

Modification of ligand binding to the Na+/K+-activated ATPase

Interactions between the ligands Mg2+, K+, and substrate and the Na+/K+-activated ATPase were examined in terms of a rapid-equilibrium, random-order, terreactant kinetic scheme for the K+-nitrophenyl phosphatase reaction that is catalyzed by this enzyme. At 37 degrees C and pH 7.5 the derived values for the dissociation constants from the free enzyme were 0.2, 0.08, and 1.4 mM for Mg2+, K+, and substrate, respectively. For Mg2+ interactions, the presence of 20% (v/v) dimethyl sulfoxide (Me2SO) increased the calculated affinity 25-fold; higher concentrations increased affinity still further. Neither reducing the temperature to 20 degrees C nor altering the pH from 6.5 to 8.3 appreciably changed the affinity for Mg2+ in the absence or presence of Me2SO. The Mg2+ sites are thus characterized by an absence of functional groups ionizable in the pH range 6.5-8.3, with binding driven by entropy changes, and with Me2SO, probably through solvation effects on the protein, increasing affinity for Mg2+ close to that for Ca2+ and Mn2+. By contrast, for K+ interactions, the presence of 20% Me2SO increased the calculated affinity only by half; moreover, reducing the temperature to 20 degrees C and the pH to 6.5 both increased affinity and diminished the response to Me2SO. The K+ sites are thus characterized by a marked sensitivity to pH and temperature, presumably through alterations in enzyme conformational equilibria that in turn are modifiable by Me2SO. Inhibition by higher concentrations of Mg2+, which varies inversely with the K+ concentration, was decreased by Me2SO. Finally, for substrate interactions, the presence of 20% Me2SO increased the calculated affinity 4-fold, and, as for Mg2+-binding, neither reducing the temperature nor varying the pH over the range 6.5-8.3 appreciably altered the affinity in the absence or presence of Me2SO. Thus, the substrate sites, like the Mg2+ sites, are characterized by an absence of functional groups ionizable in this range, with binding driven by entropy changes, and with Me2SO increasing affinity for substrate, in this case probably through favoring the partitioning of substrate from the medium into the hydrophobic active site.

Extracranial lesions of the head and neck: preliminary experience with Gd-DTPA-enhanced MR imaging

The authors report initial experience with magnetic resonance imaging enhanced with gadolinium diethylenetriaminepentaacetic acid (DTPA) in 27 patients with various extracranial lesions of the head and neck. Unenhanced T1- and T2-weighted images were compared with T1-weighted images obtained 3-30 minutes after Gd-DTPA administration. Overall, compared with precontrast T1- and T2-weighted images, Gd-DTPA improved the visibility of lesions in 11 and five of 27 patients, respectively. Gd-DTPA particularly improved the conspicuity of tumors of the nasal cavity and paranasal sinuses and tumors having perineural or intracranial extension. Gd-DTPA-enhanced images were equivalent to precontrast T1- and T2-weighted images in five and 13 patients, respectively, and inferior to them in nine and eight patients, respectively. Mixed results were obtained in two patients and one patient when Gd-DTPA-enhanced images were compared with T1- and T2-weighted images, respectively. The authors conclude that Gd-DTPA has definite but limited uses in extracranial head and neck pathologic conditions and that more research is needed to evaluate particular applications.

Pasteurella multocida corneal ulcer following a baseball injury

Pasteurella multocida is an ubiquitous organism that can be isolated from a variety of animals and birds. It is an infrequent ocular pathogen but can cause infection as a result of injury or animal exposure. This article reports a case of P multocida corneal ulcer following a baseball injury.

Solvent effects on substrate and phosphate interactions with the (Na+ + K+)-ATPase

(Na+ + K+)-ATPase activity of a dog kidney enzyme preparation was markedly inhibited by 10-30% (v/v) dimethyl sulfoxide (Me2SO) and ethylene glycol (Et(OH)2); moreover, Me2SO produced a pattern of uncompetitive inhibition toward ATP. However, K+-nitrophenylphosphatase activity was stimulated by 10-20% Me2SO and Et(OH)2 but was inhibited by 30-50%. Me2SO decreased the Km for this substrate but had little effect on the Vmax below 30% (at which concentration Vmax was then reduced). Me2SO also reduced the Ki for Pi and acetyl phosphate as competitors toward nitrophenyl phosphate but increased the Ki for ATP, CTP and 2-O-methylfluorescein phosphate as competitors. Me2SO inhibited K+-acetylphosphatase activity, although it also reduced the Km for that substrate. Finally, Me2SO increased the rate of enzyme inactivation by fluoride and beryllium. These observations are interpreted in terms of the E1P to E2P transition of the reaction sequence being associated with an increased hydrophobicity of the active site, and of Me2SO mimicking such effects by decreasing water activity: (i) primarily to stabilize the covalent E2P intermediate, through differential solvation of reactants and products, and thereby inhibiting the (Na+ + K+)-ATPase reaction and acting as a dead-end inhibitor to produce the pattern of uncompetitive inhibition; inhibiting the K+-acetylphosphatase reaction that also passes through an E2P intermediate; but not inhibiting (at lower Me2SO concentrations) the K+-nitrophenylphosphatase reaction that does not pass through such an intermediate; and (ii) secondarily to favor partitioning of Pi and non-nucleotide phosphates into the hydrophobic active site, thereby decreasing the Km for nitrophenyl phosphate and acetyl phosphate, the Ki for Pi and acetyl phosphate in the K+-nitrophenylphosphatase reaction, accelerating inactivation by fluoride and beryllium acting as phosphate analogs, and, at higher concentrations, inhibiting the K+-nitrophenylphosphatase reaction by stabilizing the non-covalent E2.P intermediate of that reaction. In addition, Me2SO may decrease binding at the adenine pocket of the low-affinity substrate site, represented as an increased Ki for ATP, CTP and 3-O-methylfluorescein phosphate.

Atheroablation with the Kensey catheter: a pathologic study

The mode of action of the Kensey catheter, a new atheroablation device, was investigated. Fresh above-the-knee amputated legs were used for recanalization of the superficial femoral artery. The variables used were identical to those of clinical trials, including a rotational speed of 50,000 rpm and an injection rate of 40 mL/min. The debris produced by the catheter was studied cytologically, and the arterial segments were examined histologically. The particle size in the debris ranged from 1 to 2,000 microns. The softer plaques produced a fine fibrin dust background with long strips of intima ranging from 10 to 2,000 microns. Complicated calcified plaques produced larger background material (10-120 microns) but smaller strips of intima (50-800 microns). Dissections and perforations occurred. Some of the debris produced by the atheroablation process was used to embolize a canine heart and kidney. Small focal infarctions were found in the heart, and large and multiple infarcts were seen in the kidney. In clinical studies the debris appears to be tolerated in the lower extremities. Its safety in the kidney and heart are questioned.

In vitro evaluation of caval filters

This experiment demonstrated the clottrapping ability of two commercially available filters, the Mobin-Uddin and Greenfield, and three experimental filters developed by Amplatz, Günther, and Gianturco. Each filter was tested in a polyethylene tube simulating the inferior vena cava. Separate series of 10 clots, each 3 cm long and 6 mm or 9.2 mm in diameter, were exposed to the test filter. The Mobin-Uddin and Amplatz filters failed by overload: acutely elevated pressures forced clots outside the skirt of the former, and between the limbs of the latter. The Günther filter trapped all incident clots, but migrated downstream when occluded by clot. The Greenfield filter passed clots at normal pressures between its widely spaced legs. The Gianturco (bird's nest) passed clots at normal pressures as well. While filters performed suboptimally, strengthening the anchoring struts of the Günther filter would result in a secure, effective filter.

Hyperglycemia is a stress response in acute stroke

To explore further the relation between admission glucose concentration and outcome in stroke, we measured glucose, fructosamine, and glycosylated hemoglobin concentrations on admission in 216 patients seen within 24 hours after the onset of their first stroke. Fructosamine concentration reflects the degree of glycemia in the preceding 4-6 weeks and glycosylated hemoglobin concentration reflects that in the preceding 3 months. Based on clinical, computed tomographic, and necropsy findings, strokes were classified as cortical infarction, lacunar infarction, or intracerebral hemorrhage. Analyses were done including and excluding 47 diabetic patients. No correlation between neurologic outcome as mortality and fructosamine or glycosylated hemoglobin concentration was found. Survival showed a significant correlation with admission glucose concentration only for patients with intracerebral hemorrhage. Our results suggest that hyperglycemia is unlikely to worsen the outcome of acute stroke and that hyperglycemia probably represents either a latent diabetic state or a stress response.

Characteristics of 3-O-methylfluorescein phosphate hydrolysis by the (Na+ + K+)-ATPase

With 3-O-methylfluorescein phosphate (3-OMFP) as substrate for the phosphatase reaction catalyzed by the (Na+ + K+)-ATPase, a number of properties of that reaction differ from those with the common substrate p-nitrophenyl phosphate (NPP): the Km is 2 orders of magnitude less and the Vmax is two times greater, and dimethyl sulfoxide (Me2SO) inhibits rather than stimulates. In addition, reducing the incubation pH decreases both the Km and Vmax for K+-activated 3-OMFP hydrolysis as well as the K0.5 for K+ activation. However, reducing the incubation pH increases inhibition by Pi and the Vmax for 3-OMFP hydrolysis in the absence of K+. When choline chloride is varied reciprocally with NaCl to maintain the ionic strength constant, NaCl inhibits K+-activated 3-OMFP hydrolysis modestly with 10 mM KCl, but stimulates (in the range 5-30 mM NaCl) with suboptimal (0.35 mM) KCl. In the absence of K+, however, NaCl stimulates increasingly over the range 5-100 mM when the ionic strength is held constant. These observations are interpreted in terms of (a) differential effects of the ligands on enzyme conformations; (b) alternative reaction pathways in the absence of Na+, with a faster, phosphorylating pathway more readily available to 3-OMFP than to NPP; and (c) a (Na+ + K+)-phosphatase pathway, most apparent at suboptimal K+ concentrations, that is also more readily available to 3-OMFP.

Identification of some abnormal haemoglobins by fast atom bombardment mass spectrometry and fast atom bombardment tandem mass spectrometry

The characterization of two abnormal human haemoglobins by fast atom bombardment (FAB) mapping is presented. The first variant, called 'R', exhibits a tryptic FAB map identical to that of normal haemoglobin. However, using Staphylococcus protease V8, a peptide containing the carboxyl end of the beta-chain exhibits a mass shift down to 300 mass units. This clearly indicates the deletion of the two last amino acids of the beta-chain. The second variant, called 'Grenoble', is due to two different modifications of the beta-chain. The location of the Pro----Ser exchange on peptide T5 is achieved by the collisionally activated dissociation mass analyzed ion kinetic energy spectra of the corresponding [MH]+ ion. The m/z value of that peptide indicated a supplementary acid----amide modification, which was located by amino acid sequencing using chemical methods. This work concludes with the necessity of using complementary methods for achieving rapid determinations of abnormal proteins with minute amounts.

Phenytoin dosing in obese patients: two case reports

Phenytoin is used extensively in the treatment of various forms of epilepsy, and remains the drug of choice in partial and generalized tonic-clonic seizures. Because it demonstrates saturable, Michaelis-Menten pharmacokinetics, dosing of phenytoin within the therapeutic range can be very challenging, especially so in obese patients. We present case reports of two obese patients each requiring very large doses of phenytoin sodium (1000 mg/d) to sustain therapeutic serum concentrations and seizure control. There are very few reports in the literature regarding phenytoin pharmacokinetic changes in the obese. We can only theorize possible changes in these parameters. Further investigation in the form of controlled research trials need to be performed before final dosage recommendations can be given.

Substrate sites of the (Na+ + K+)-ATPase: pertinence of the adenine and fluorescein binding sites

The (Na+ + K+)-activated ATPase catalyzes the K+-activated hydrolysis of 3-O-methylfluorescein phosphate (3OMFP) with a Km of 50 microM, nearly two orders of magnitude lower than the Km for nitrophenyl phosphate, 3 mM. Both ATP and nitrophenyl phosphate are competitors toward 3OMFP with Ki values corresponding to their Km values (for ATP that at the low-affinity sites of the E2 conformation). Enzyme treated with fluorescein isothiocyanate (FITC) such that 60% of the (Na+ + K+)-ATPase activity is lost still hydrolyzes both 3OMFP and nitrophenyl phosphate: the apparent Km values are increased less than 2-fold and the Vmax is unaffected. ATP still inhibits these K+-phosphatase reactions of the FITC-treated enzyme, and this inhibition can exceed the 40% of residual (Na+ + K+)-ATPase activity. Evaluation of a kinetic model indicates that the Ki for ATP is increased about an order of magnitude by FITC-binding. Similar results obtain with trinitrophenyl-ATP (TNP-ATP) as inhibitor, in this case with Ki values in the micromolar range. Finally, FITC treatment increases K+-activated ADPase activity. These observations are interpreted as the fluorescein ring of 3OMFP binding to the adenine pocket of the substrate site, thereby conferring high affinity, just as the fluorescein ring of FITC binding to the adenine pocket in the E1 conformation permits specific linkage of the isothiocyanate chain to a particular lysine, Lys-501. Then, coincident with the transition to the E2 conformation, which bears the low-affinity site for ATP and which catalyzes the K+-phosphatase reaction, the FITC molecule tethered to Lys-501 is pulled from the adenine pocket: allowing 3OMFP and ADP to bind as substrates and ATP and TNP-ATP as inhibitors, albeit in altered conformation. The E1 to E2 transition thus involves not only a change from high to low affinity for ATP, but also a distortion of the adenine pocket and the orientation between Lys-501 and Asp-369, the residue associated with catalysis.