Alcohol Consumption and Common Carotid Intima-Media Thickness: The USE-IMT Study

Aims

Epidemiological evidence indicates a protective effect of light to moderate alcohol consumption compared to non-drinking and heavy drinking. Although several mechanisms have been suggested, the effect of alcohol on atherosclerotic changes in vessel walls is unclear. Therefore, we explored the relationship between alcohol consumption and common carotid intima media thickness, a marker of early atherosclerosis in the general population.

Methods

Individual participant data from eight cohorts, involving 37,494 individuals from the USE-IMT collaboration were used. Multilevel age and sex adjusted linear regression models were applied to estimate mean differences in common carotid intima-media thickness (CIMT) with alcohol consumption.

Results

The mean age was 57.9 years (SD 8.6) and the mean CIMT was 0.75 mm (SD 0.177). About, 40.5% reported no alcohol consumed, and among those who drank, mean consumption was 13.3 g per day (SD 16.4). Those consuming no alcohol or a very small amount (<5 g per day) had significantly lower common CIMT values than those consuming >10 g per day, after adjusting for a range of confounding factors.

Conclusion

In this large CIMT consortium, we did not find evidence to support a protective effect of alcohol on CIMT.

Race/Ethnic Differences in the Associations of the Framingham Risk Factors with Carotid IMT and Cardiovascular Events

Background

Clinical manifestations and outcomes of atherosclerotic disease differ between ethnic groups. In addition, the prevalence of risk factors is substantially different. Primary prevention programs are based on data derived from almost exclusively White people. We investigated how race/ethnic differences modify the associations of established risk factors with atherosclerosis and cardiovascular events.

Methods

We used data from an ongoing individual participant meta-analysis involving 17 population-based cohorts worldwide. We selected 60,211 participants without cardiovascular disease at baseline with available data on ethnicity (White, Black, Asian or Hispanic). We generated a multivariable linear regression model containing risk factors and ethnicity predicting mean common carotid intima-media thickness (CIMT) and a multivariable Cox regression model predicting myocardial infarction or stroke. For each risk factor we assessed how the association with the preclinical and clinical measures of cardiovascular atherosclerotic disease was affected by ethnicity.

Results

Ethnicity appeared to significantly modify the associations between risk factors and CIMT and cardiovascular events. The association between age and CIMT was weaker in Blacks and Hispanics. Systolic blood pressure associated more strongly with CIMT in Asians. HDL cholesterol and smoking associated less with CIMT in Blacks. Furthermore, the association of age and total cholesterol levels with the occurrence of cardiovascular events differed between Blacks and Whites.

Conclusion

The magnitude of associations between risk factors and the presence of atherosclerotic disease differs between race/ethnic groups. These subtle, yet significant differences provide insight in the etiology of cardiovascular disease among race/ethnic groups. These insights aid the race/ethnic-specific implementation of primary prevention.

Common Carotid Intima-Media Thickness Relates to Cardiovascular Events in Adults Aged <45 Years

Although atherosclerosis starts in early life, evidence on risk factors and atherosclerosis in individuals aged <45 years is scarce. Therefore, we studied the relationship between risk factors, common carotid intima-media thickness (CIMT), and first-time cardiovascular events in adults aged <45 years. Our study population consisted of 3067 adults aged <45 years free from symptomatic cardiovascular disease at baseline, derived from 6 cohorts that are part of the USE-IMT initiative, an individual participant data meta-analysis of general-population–based cohort studies evaluating CIMT measurements. Information on risk factors, CIMT measurements, and follow-up of the combined end point (first-time myocardial infarction or stroke) was obtained. We assessed the relationship between risk factors and CIMT and the relationship between CIMT and first-time myocardial infarction or stroke using a multivariable linear mixed-effects model and a Cox proportional-hazards model, respectively. During a follow-up of 16.3 years, 55 first-time myocardial infarctions or strokes occurred. Median CIMT was 0.63 mm. Of the risk factors under study, age, sex, diastolic blood pressure, body mass index, total cholesterol, and high-density lipoprotein cholesterol related to CIMT. Furthermore, CIMT related to first-time myocardial infarction or stroke with a hazard ratio of 1.40 per SD increase in CIMT, independent of risk factors (95% confidence interval, 1.11–1.76). CIMT may be a valuable marker for cardiovascular risk in adults aged <45 years who are not yet eligible for standard cardiovascular risk screening. This is especially relevant in those with an increased, unfavorable risk factor burden.

Airway turbulence and changes in upper airway hydraulic diameter can be estimated from the intensity of high frequency inspiratory sounds in sleeping adults

Obstructive sleep disordered breathing can cause death and significant morbidity in adults and children. We previously found that children with smaller upper airways (measured by magnetic resonance imaging while awake) generated loud high frequency inspiratory sounds (HFIS, defined as inspiratory sounds > 2 kHz) while they slept. The purpose of this study was (1) to determine what characteristics of airflow predicted HFIS intensity, and (b) to determine if we could calculate changes in hydraulic diameter (D) in both an in vitro model and in the upper airways of sleeping humans. In an in vitro model, high frequency sound intensity was an estimate of airflow turbulence as reflected by the Reynold's number (Re). D of the in vitro model was calculated using Re, the pressure gradient, Swamee-Jain formula and Darcy formula. D was proportional to but smaller than the actual diameters (r(2) = 0.94). In humans, we measured HFIS intensity and the pressure gradient across the upper airway (estimated with oesophageal pressure, Pes) during polysomnography in four adult volunteers and applied the same formulae to calculate D. At apnoea termination when the airway opens, we observed (1) an increase in HFIS intensity suggesting an increase in turbulence (higher Re), and (2) a larger calculated D. This method allows dynamic estimation of changes in relative upper airway hydraulic diameter (D) in sleeping humans with narrowed upper airways.

Common carotid intima-media thickness measurements do not improve cardiovascular risk prediction in individuals with elevated blood pressure: the USE-IMT collaboration

Carotid intima-media thickness (CIMT) is a marker of cardiovascular risk. It is unclear whether measurement of mean common CIMT improves 10-year risk prediction of first-time myocardial infarction or stroke in individuals with elevated blood pressure. We performed an analysis among individuals with elevated blood pressure (i.e., a systolic blood pressure ≥140 mm Hg and a diastolic blood pressure ≥ 90 mm Hg) in USE-IMT, a large ongoing individual participant data meta-analysis. We refitted the risk factors of the Framingham Risk Score on asymptomatic individuals (baseline model) and expanded this model with mean common CIMT (CIMT model) measurements. From both models, 10-year risks to develop a myocardial infarction or stroke were estimated. In individuals with elevated blood pressure, we compared discrimination and calibration of the 2 models and calculated the net reclassification improvement (NRI). We included 17 254 individuals with elevated blood pressure from 16 studies. During a median follow-up of 9.9 years, 2014 first-time myocardial infarctions or strokes occurred. The C-statistics of the baseline and CIMT models were similar (0.73). NRI with the addition of mean common CIMT was small and not significant (1.4%; 95% confidence intervals, -1.1 to 3.7). In those at intermediate risk (n=5008, 10-year absolute risk of 10% to 20%), the NRI was 5.6% (95% confidence intervals, 1.6-10.4). There is no added value of measurement of mean common CIMT in individuals with elevated blood pressure for improving cardiovascular risk prediction. For those at intermediate risk, the addition of mean common CIMT to an existing cardiovascular risk score is small but statistically significant.

Extracellular superoxide dismutase ameliorates skeletal muscle abnormalities, cachexia, and exercise intolerance in mice with congestive heart failure

BACKGROUND

Congestive heart failure (CHF) is a leading cause of morbidity and mortality, and oxidative stress has been implicated in the pathogenesis of cachexia (muscle wasting) and the hallmark symptom, exercise intolerance. We have previously shown that a nitric oxide-dependent antioxidant defense renders oxidative skeletal muscle resistant to catabolic wasting. Here, we aimed to identify and determine the functional role of nitric oxide-inducible antioxidant enzyme(s) in protection against cardiac cachexia and exercise intolerance in CHF.

METHODS AND RESULTS

We demonstrated that systemic administration of endogenous nitric oxide donor S-nitrosoglutathione in mice blocked the reduction of extracellular superoxide dismutase (EcSOD) protein expression, as well as the induction of MAFbx/Atrogin-1 mRNA expression and muscle atrophy induced by glucocorticoid. We further showed that endogenous EcSOD, expressed primarily by type IId/x and IIa myofibers and enriched at endothelial cells, is induced by exercise training. Muscle-specific overexpression of EcSOD by somatic gene transfer or transgenesis (muscle creatine kinase [MCK]-EcSOD) in mice significantly attenuated muscle atrophy. Importantly, when crossbred into a mouse genetic model of CHF (α-myosin heavy chain-calsequestrin), MCK-EcSOD transgenic mice had significant attenuation of cachexia with preserved whole body muscle strength and endurance capacity in the absence of reduced HF. Enhanced EcSOD expression significantly ameliorated CHF-induced oxidative stress, MAFbx/Atrogin-1 mRNA expression, loss of mitochondria, and vascular rarefaction in skeletal muscle.

CONCLUSIONS

EcSOD plays an important antioxidant defense function in skeletal muscle against cardiac cachexia and exercise intolerance in CHF.

Abstract W P349: Prediction of Major Adverse Cardiovascular Events by Age-Normalized Carotid Intimal Medial Thickness

Background: Increases in carotid intimal medial thickness (CIMT), as measured by noninvasive ultrasonography, have been associated with increased risk of myocardial infarction and stroke. From 706 patients who had CIMT measured between 1995 and 2003 at the University of Virginia, we created age-specific quartiles of carotid thickness. Over a mean follow-up of 4.8 years, we found that bulb and internal but not common CIMT predicted the combined endpoint of myocardial infarction, stroke, and revascularization (Atherosclerosis 187:186, 2006). We now present the analysis as of 2012 for CIMT to predict major adverse cardiovascular events in a population of patients referred for carotid IMT measurement.

Methods: From 1995-2012, 1427 patients had carotid IMT measured at the University of Virginia’s Preventive Cardiology practice. In 2012, we successfully contacted 1259 of these patients to determine clinical outcomes. The 1259 patients were entered into a database and odds ratios were calculated with logistic regression in SAS.

Results: Over a mean follow-up period of 7.8 years (range, 1 to 16), 30 patients died and 66 had major adverse cardiovascular events (MACE): 17 patients had CV death/myocardial infarction; 20 required revascularization; and 29 had a stroke or transient ischemic attack.

The highest quartile of bulb CIMT demonstrated an odds ratio for MACE of 7.2 (95% confidence interval, 3.0 to 18.6; P<0.001) when compared to the quartile with the lowest thickness (P<0.001 for trend).

The highest quartile of internal CIMT demonstrated an odds ratio for MACE of 3.1 (95% confidence interval, 1.2 to 8.3; P=0.02) when compared to the quartile with the lowest thickness (P=0.009 for trend).

Common carotid IMT did not significantly predict MACE (p=0.23).

The highest quartile of bulb CIMT demonstrated an odds ratio for mortality of 3.4 (95% confidence interval, 1.03 to 11.2; P=0.044) when compared to the quartile with the lowest thickness (not significant for common or internal CIMT).

Conclusions: Age-normalized measurement of bulb and internal but not common CIMT appear to predict which individuals would most benefit from aggressive risk-factor modification.

Mechanisms involved in increased sensitivity to adenosine A(2A) receptor activation and hypoxia-induced vasodilatation in porcine coronary arteries

Hypoxia-induced coronary vasorelaxation is a compensatory mechanism increasing blood flow. We hypothesized that hypoxia shares pathways with adenosine and causes vasorelaxation through the adenosine A(2A) receptor and force suppression by increasing cAMP and phosphorylated heat shock protein (HSP)20. Adenosine receptors in porcine left anterior descending coronary arteries (LAD) were examined by RT-PCR and isometric tension recording in myographs. Vasorelaxation was induced by adenosine, 1% oxygen, or both in the absence or presence of ZM241385, an adenosine A(2A) receptor antagonist. cAMP was determined by ELISA and p-HSP20/HSP20 and p-MLC/MLC were determined by immunoblotting and densitometric analyses. In coronary arteries exposed to 1% oxygen, there was increased sensitivity to adenosine, the adenosine A2 selective agonist NECA, and the adenosine A(2A) selective receptor agonist CGS21680. ZM241385 shifted concentration-response curves for CGS21680 to the right, whereas the adenosine A1 antagonist DPCPX, the adenosine A2B receptor antagonist MRS1754 and the adenosine A3 receptor antagonist MRS1523 failed to reduce vasodilatation induced by CGS21680. 1% oxygen or adenosine increased cAMP accumulation and HSP20 phosphorylation without changing T850-MYPT1 and MLC phosphorylation. ZM241385 failed to change 1% oxygen-induced vasodilation, cAMP accumulation, HSP20 phosphorylation and MLC phosphorylation. The PKA inhibitor Rp-8-CPT-cAMPS significantly reduced vasorelaxation induced by 1% oxygen or CGS21680. Our findings suggest that the increased sensitivity to adenosine, NECA, and CGS21680 at 1% oxygen involves adenosine A(2A) receptors. Adenosine and 1% oxygen induce vasorelaxation in PGF2α-contracted porcine coronary arteries partly by force suppression caused by increased cAMP and phosphorylation of HSP20.

Common carotid intima-media thickness does not add to Framingham risk score in individuals with diabetes mellitus: the USE-IMT initiative

AIMS/HYPOTHESIS

The aim of this work was to investigate whether measurement of the mean common carotid intima-media thickness (CIMT) improves cardiovascular risk prediction in individuals with diabetes.

METHODS

We performed a subanalysis among 4,220 individuals with diabetes in a large ongoing individual participant data meta-analysis involving 56,194 subjects from 17 population-based cohorts worldwide. We first refitted the risk factors of the Framingham heart risk score on the individuals without previous cardiovascular disease (baseline model) and then expanded this model with the mean common CIMT (CIMT model). The absolute 10 year risk for developing a myocardial infarction or stroke was estimated from both models. In individuals with diabetes we compared discrimination and calibration of the two models. Reclassification of individuals with diabetes was based on allocation to another cardiovascular risk category when mean common CIMT was added.

RESULTS

During a median follow-up of 8.7 years, 684 first-time cardiovascular events occurred among the population with diabetes. The C statistic was 0.67 for the Framingham model and 0.68 for the CIMT model. The absolute 10 year risk for developing a myocardial infarction or stroke was 16% in both models. There was no net reclassification improvement with the addition of mean common CIMT (1.7%; 95% CI -1.8, 3.8). There were no differences in the results between men and women.

CONCLUSIONS/INTERPRETATION

There is no improvement in risk prediction in individuals with diabetes when measurement of the mean common CIMT is added to the Framingham risk score. Therefore, this measurement is not recommended for improving individual cardiovascular risk stratification in individuals with diabetes.

Slack length reduces the contractile phenotype of the Swine carotid artery

Contraction is the primary function of adult arterial smooth muscle. However, in response to vessel injury or inflammation, arterial smooth muscle is able to phenotypically modulate from the contractile state to several 'synthetic' states characterized by proliferation, migration and/or increased cytokine secretion. We examined the effect of tissue length (L) on the phenotype of intact, isometrically held, initially contractile swine carotid artery tissues. Tissues were studied (1) without prolonged incubation at the optimal length for force generation (1.0 Lo, control), (2) with prolonged incubation for 17 h at 1.0 Lo, or (3) with prolonged incubation at slack length (0.6 Lo) for 16 h and then restoration to 1.0 Lo for 1 h. Prolonged incubation at 1.0 Lo minimally reduced the contractile force without substantially altering the mediators of contraction (crossbridge phosphorylation, shortening velocity or stimulated actin polymerization). Prolonged incubation of tissues at slack length (0.6 Lo), despite return of length to 1.0 Lo, substantially reduced contractile force, reduced crossbridge phosphorylation, nearly abolished crossbridge cycling (shortening velocity) and abolished stimulated actin polymerization. These data suggest that (1) slack length treatment significantly alters the contractile phenotype of arterial tissue, and (2) slack length treatment is a model to study acute phenotypic modulation of intact arterial smooth muscle.

Common carotid intima-media thickness measurements in cardiovascular risk prediction: a meta-analysis

CONTEXT

The evidence that measurement of the common carotid intima-media thickness (CIMT) improves the risk scores in prediction of the absolute risk of cardiovascular events is inconsistent.

OBJECTIVE

To determine whether common CIMT has added value in 10-year risk prediction of first-time myocardial infarctions or strokes, above that of the Framingham Risk Score.

DATA SOURCES

Relevant studies were identified through literature searches of databases (PubMed from 1950 to June 2012 and EMBASE from 1980 to June 2012) and expert opinion.

STUDY SELECTION

Studies were included if participants were drawn from the general population, common CIMT was measured at baseline, and individuals were followed up for first-time myocardial infarction or stroke.

DATA EXTRACTION

Individual data were combined into 1 data set and an individual participant data meta-analysis was performed on individuals without existing cardiovascular disease.

RESULTS

We included 14 population-based cohorts contributing data for 45,828 individuals. During a median follow-up of 11 years, 4007 first-time myocardial infarctions or strokes occurred. We first refitted the risk factors of the Framingham Risk Score and then extended the model with common CIMT measurements to estimate the absolute 10-year risks to develop a first-time myocardial infarction or stroke in both models. The C statistic of both models was similar (0.757; 95% CI, 0.749-0.764; and 0.759; 95% CI, 0.752-0.766). The net reclassification improvement with the addition of common CIMT was small (0.8%; 95% CI, 0.1%-1.6%). In those at intermediate risk, the net reclassification improvement was 3.6% in all individuals (95% CI, 2.7%-4.6%) and no differences between men and women.

CONCLUSION

The addition of common CIMT measurements to the Framingham Risk Score was associated with small improvement in 10-year risk prediction of first-time myocardial infarction or stroke, but this improvement is unlikely to be of clinical importance.

Tissue length modulates "stimulated actin polymerization," force augmentation, and the rate of swine carotid arterial contraction

"Stimulated actin polymerization" has been proposed to be involved in force augmentation, in which prior submaximal activation of vascular smooth muscle increases the force of a subsequent maximal contraction by ∼15%. In this study, we altered stimulated actin polymerization by adjusting tissue length and then measured the effect on force augmentation. At optimal tissue length (1.0 L(o)), force augmentation was observed and was associated with increased prior stimulated actin polymerization, as evidenced by increased prior Y118 paxillin phosphorylation without changes in prior S3 cofilin or cross-bridge phosphorylation. Tissue length, per se, regulated Y118 paxillin, but not S3 cofilin, phosphorylation. At short tissue length (0.6 L(o)), force augmentation was observed and was associated with increased prior stimulated actin polymerization, as evidenced by reduced prior S3 cofilin phosphorylation without changes in Y118 paxillin or cross-bridge phosphorylation. At long tissue length (1.4 L(o)), force augmentation was not observed, and there were no prior changes in Y118 paxillin, S3 cofilin, or cross-bridge phosphorylation. There were no significant differences in the cross-bridge phosphorylation transients before and after the force augmentation protocol at all three lengths tested. Tissues contracted faster at longer tissue lengths; contractile rate correlated with prior Y118 paxillin phosphorylation. Total stress, per se, predicted Y118 paxillin phosphorylation. These data suggest that force augmentation is regulated by stimulated actin polymerization and that stimulated actin polymerization is regulated by total arterial stress. We suggest that K(+) depolarization first leads to cross-bridge phosphorylation and contraction, and the contraction-induced increase in mechanical strain increases Y118 paxillin phosphorylation, leading to stimulated actin polymerization, which further increases force, i.e., force augmentation and, possibly, latch.

Force augmentation and stimulated actin polymerization in swine carotid artery

The phenomenon of posttetanic potentiation, in which a single submaximal contraction or series of submaximal contractions strengthens a subsequent contraction, has been observed in both skeletal and cardiac muscle. In this study, we describe a similar phenomenon in swine carotid arterial smooth muscle. We find that a submaximal K(+) depolarization increases the force generation of a subsequent maximal K(+) depolarization; we term this "force augmentation." Force augmentation was not associated with a significant increase in crossbridge phosphorylation or shortening velocity during the maximal K(+) depolarization, suggesting that the augmented force was not caused by higher crossbridge phosphorylation or crossbridge cycling rates. We found that the characteristics of the tissue before the maximal K(+) depolarization predicted the degree of force augmentation. Specifically, measures of stimulated actin polymerization (higher prior Y118 paxillin phosphorylation, higher prior F-actin, and transition to a more solid rheology evidenced by lower noise temperature, hysteresivity, and phase angle) predicted the subsequent force augmentation. Increased prior contraction alone did not induce force augmentation since readdition of Ca(2+) to Ca(2+)-depleted tissues induced a partial contraction that was not associated with changes in noise temperature or with subsequent force augmentation. These data suggest that stimulated actin polymerization may produce a substrate for increased crossbridge mediated force, a process we observe as force augmentation.

To statin or to non-statin in coronary disease—considering absolute risk is the answer

The newest guidelines for treating people with coronary artery disease (CAD) suggest benefit from statin-induced LDL cholesterol lowering regardless of baseline LDL cholesterol level. These guidelines were based on recent clinical trials that showed statistically significant statin-induced relative risk reductions (RRR) in cardiovascular events. However, there are proven "non-statin" anti-atherosclerotic treatments. This analysis was designed to allow the physician to decide which patients benefit from the various anti-atherosclerotic treatments available. Analysis is presented as absolute risk reduction (ARR) because ARR takes baseline risk into account. There was a large benefit from statin therapy in stable CAD when LDL cholesterol levels were high. There were diminishing returns, despite statistically significance, with statin treatment of people with chronic CAD and lower LDL cholesterol levels. People with chronic CAD and lower LDL cholesterol levels had at least as much and possibly twice the ARR when treated with niacin or gemfibrozil as that would occur with statin treatment. For the first year after the acute coronary syndrome, risk was higher than in stable CAD, and trials showed a benefit especially with a Mediterranean diet and also with statin therapy that reduced LDL cholesterol levels to approximately 80 mg dl(-1). The Mediterranean diet was also beneficial in chronic CAD. These results suggest that both statin and non-statin therapy are important for reducing the sequelae of atherosclerosis.

Phospholemman does not participate in forskolin-induced swine carotid artery relaxation

Phosphorylation of phospholemman (PLM) on ser68 has been proposed to at least partially mediate cyclic AMP (cAMP) mediated relaxation of arterial smooth muscle. We evaluated the time course of the phosphorylation of phospholemman (PLM) on ser68, myosin regulatory light chains (MRLC) on ser19, and heat shock protein 20 (HSP20) on ser16 during a transient forskolin-induced relaxation of histamine-stimulated swine carotid artery. We also evaluated the dose response for forskolin- and nitroglycerin-induced relaxation in phenylephrine-stimulated PLM-/- and PLM+/+ mice. The time course for changes in ser19 MRLC dephosphorylation and ser16 HSP20 phosphorylation was appropriate to explain the forskolin-induced relaxation and the recontraction observed upon washout of forskolin. However, the time course for changes in ser68 PLM phosphorylation was too slow to explain forskolin-induced changes in force. There was no difference in the phenylephrine contractile dose response or in forskolin-induced relaxation dose response observed in PLM-/- and PLM+/+ aortae. In aortae precontracted with phenylephrine, nitroglycerin induced a slightly, but significantly greater relaxation in PLM-/- compared to PLM+/+ aortae. These data are consistent with the hypothesis that ser19 MRLC dephosphorylation and ser16 HSP20 phosphorylation are involved in forskolin-induced relaxation. Our data suggest that PLM phosphorylation is not significantly involved in forskolin-induced arterial relaxation.

Paxillin phosphorylation, actin polymerization, noise temperature, and the sustained phase of swine carotid artery contraction

Histamine stimulation of swine carotid artery induces both contraction and actin polymerization. The importance of stimulus-induced actin polymerization is not known. Tyrosine phosphorylation of the scaffolding protein paxillin is thought to be an important regulator of actin polymerization. Noise temperature, hysteresivity, and phase angle are rheological measures of the fluidity of a tissue, i.e., whether the muscle is more a "Hookean solid" or a "Newtonian liquid." Y118 paxillin phosphorylation, crossbridge phosphorylation, actin polymerization, noise temperature, hysteresivity, phase angle, real stiffness, and stress were measured in intact swine carotid arteries that were depolarized with high K(+) or stimulated with histamine. The initial rapid force development phase of high-K(+) or histamine-induced contraction was associated with increased crossbridge phosphorylation but no significant change in Y118 paxillin phosphorylation, actin polymerization, noise temperature, hysteresivity, or phase angle. This suggests that the initial contraction was caused by the increase in crossbridge phosphorylation and did not alter the tissue's rheology. Only after full force development was there a significant increase in Y118 paxillin phosphorylation and actin polymerization associated with a significant decrease in noise temperature and hysteresivity. These data suggest that some part of the sustained contraction may depend on stimulated actin polymerization and/or a transition to a more "solid" rheology. Supporting this contention was the finding that an inhibitor of actin polymerization, latrunculin-A, reduced force while increasing noise temperature/hysteresivity. Further research is needed to determine whether Y118 paxillin phosphorylation, actin polymerization, and changes in rheology could have a role in arterial smooth muscle contraction.

Force suppression and the crossbridge cycle in swine carotid artery

Cyclic nucleotides can relax arterial smooth muscle without reductions in crossbridge phosphorylation, a process termed force suppression. There are two potential mechanisms for force suppression: 1) phosphorylated crossbridges binding to thin filaments could be inhibited or 2) the attachment of thin filaments to anchoring structures could be disrupted. These mechanisms were evaluated by comparing histamine-stimulated swine arterial smooth muscle with and without forskolin-induced force suppression and with and without latrunculin-A-induced actin filament disruption. At matched force, force suppression was associated with higher crossbridge phosphorylation and shortening velocity at low loads when compared with tissues without force suppression. Shortening velocity at high loads, noise temperature, hysteresivity, and stiffness did not differ with and without force suppression. These data suggest that crossbridge phosphorylation regulates the crossbridge cycle during force suppression. Actin disruption with latrunculin-A was associated with higher crossbridge phosphorylation when compared with tissues without actin disruption. Shortening velocity, noise temperature, hysteresivity, and stiffness did not differ with and without actin disruption. These data suggest that actin disruption interferes with regulation of crossbridge cycling by crossbridge phosphorylation. Stiffness was linearly dependent on stress, suggesting that the force per attached crossbridge was not altered with force suppression or actin disruption. These data suggest a difference in the mechanical characteristics observed during force suppression and actin disruption, implying that force suppression does not mechanistically involve actin disruption. These data are most consistent with a model where force suppression involves the inhibition of phosphorylated crossbridge binding to thin filaments.

Longer muscle lengths recapitulate force suppression in swine carotid artery

Cyclic nucleotide can relax arterial smooth muscle without reductions in myosin regulatory light chain (MRLC) phosphorylation, a process termed force suppression. Smooth muscle contractile force also depends on tissue length. It is not known how tissue length affects force suppression. Swine carotid artery rings were equilibrated at various lengths (as a fraction of L(o), the optimal length for force development). They were then frozen during contractile activation with or without forskolin-induced relaxation. Frozen tissue homogenates were then analyzed for Ser(19)-MRLC phosphorylation and Ser(16)-heat shock protein 20 (HSP20) phosphorylation (HSP20 is the proposed mediator of force suppression). Higher values of MRLC phosphorylation were required to induce a histamine contraction at longer tissue lengths. At 1.4 L(o), the dependence of force on MRLC phosphorylation observed with histamine stimulation alone was shifted to the right, a response similar to that observed during force suppression at 1.0 L(o). The rightward shift in the dependence of force on MRLC phosphorylation seen with histamine stimulation alone at 1.4 L(o) was not associated with increased HSP20 phosphorylation. Addition of forskolin to histamine-stimulated tissues at 1.4 L(o) induced a relaxation associated with increased HSP20 phosphorylation and reduced MRLC phosphorylation, i.e., there was no additional force suppression. At shorter tissue lengths (0.6 L(o)), the dependence of force on MRLC phosphorylation with histamine stimulation alone was steep, a response similar to that observed during normal contractile activation at 1.0 L(o). Addition of forskolin induced force suppression at 0.6 L(o). The sensitivity of swine carotid to the concentration of histamine was greater at longer tissue lengths compared with shorter tissue lengths, suggesting a physiological mechanism to restore optimal tissue length. These data suggest that longer tissue lengths induced a force suppression-like state that was 1) not additive with forskolin and 2) not associated with HSP20 phosphorylation. Further research is required to determine this length-dependent mechanism.

Increased Expression of Heat Shock Protein 20 and Decreased Contractile Stress in Obstructed Rat Bladder

PURPOSE

Bladder outlet obstruction induces detrusor hypertrophy and it can eventually lead to decreased bladder smooth muscle contractility. Heat shock protein 20 is the proposed mediator of force suppression in vascular smooth muscle. We investigated whether heat shock protein 20 could also mediate the decreased contractility observed in partially obstructed rat bladders.

MATERIALS AND METHODS

Female Wistar rats (Harlan Laboratories, Indianapolis, Indiana) were randomized to partial urethral ligation or sham ligation. After 3 weeks the rats were sacrificed, and the bladders were harvested, frozen, homogenized and analyzed for heat shock protein 20 content by Western blot immunoreactivity. The content of myosin regulatory light chain, a constitutively expressed protein, was determined as a control. Bladder smooth muscle strips were dissected from some rats and mounted for force generation measurement.

RESULTS

At cystectomy obstructed bladders were significantly heavier and had more residual urine compared to sham operated bladders. Heat shock protein 20 immunoreactivity was significantly increased a mean +/- 1 SEM of 1.9 +/- 0.3-fold in obstructed vs sham operated bladders. Control protein myosin regulatory light chain immunoreactivity did not significantly differ in obstructed and sham operated bladders. Maximal stress, that is force per cross-sectional area, was significantly decreased in obstructed vs sham operated bladders. Human bladder was found to express immunoreactive heat shock protein 20.

CONCLUSIONS

We noted that partially obstructed rat bladders 1) express higher levels of heat shock protein 20 and 2) generate less stress than sham operated bladders. These data suggest the possibility that heat shock protein 20 over expression could at least partially mediate the decreased contractile activity observed with partial bladder outlet obstruction. The mechanism for increased heat shock protein 20 expression is unknown but it may involve increased mechanical stress or hypoxia from urethral obstruction. Human bladder expressed immunoreactive heat shock protein 20, suggesting that a similar mechanism could potentially occur in humans. If confirmed in humans, patients with clinical conditions that result in detrusor hypocontractility could potentially benefit from pharmacological interventions aimed at inhibiting heat shock protein 20.

Prediction of major adverse cardiovascular events by age-normalized carotid intimal medial thickness

BACKGROUND

Increases in carotid intimal medial thickness (IMT), as measured by noninvasive ultrasonography, have been associated with increased risk of myocardial infarction and stroke, particularly in adults 65 years of age or older. We investigated the value of age-normalized carotid IMT measurements in predicting major adverse cardiovascular events in a population of patients referred for carotid IMT measurement.

METHODS

Since 1995, 727 patients had carotid IMT measured at the University of Virginia's Preventive Cardiology practice. We successfully contacted 706 of these patients to determine clinical outcomes; 21 patients were lost to follow-up. The 706 patients were entered into a database, age-specific quartiles of carotid thickness developed, and odds ratios were calculated with logistic regression.

RESULTS

Over a mean follow-up period of 4.78 years (range, 2.0-9.3 years), 20 patients had major adverse cardiovascular events: seven patients had myocardial infarctions; seven required revascularization; and six had a stroke or transient ischemic attack. The incidence of events directly correlated with age-normalized measurements of carotid bulb and internal carotid IMT. The highest quartile of carotid bulb IMT demonstrated an odds ratio for all events of 5.8 (95% confidence interval, 1.3-26.6; P = 0.023) when compared to the quartile with the lowest thickness (P = 0.007 for trend). A similar trend for quartiles of internal carotid IMT was also observed (P = 0.03). Common carotid IMT did not significantly predict events.

CONCLUSIONS

Age-normalized measurement of carotid bulb and internal carotid IMT may be helpful in determining which individuals would most benefit from aggressive risk-factor modification.

The latch-bridge hypothesis of smooth muscle contraction

In contrast to striated muscle, both normalized force and shortening velocities are regulated functions of cross-bridge phosphorylation in smooth muscle. Physiologically this is manifested as relatively fast rates of contraction associated with transiently high levels of cross-bridge phosphorylation. In sustained contractions, Ca2+, cross-bridge phosphorylation, and ATP consumption rates fall, a phenomenon termed "latch". This review focuses on the Hai and Murphy (1988a) model that predicted the highly non-linear dependence of force on phosphorylation and a directly proportional dependence of shortening velocity on phosphorylation. This model hypothesized that (i) cross-bridge phosphorylation was obligatory for cross-bridge attachment, but also that (ii) dephosphorylation of an attached cross-bridge reduced its detachment rate. The resulting variety of cross-bridge cycles as predicted by the model could explain the observed dependencies of force and velocity on cross-bridge phosphorylation. New evidence supports modifications for more general applicability. First, myosin light chain phosphatase activity is regulated. Activation of myosin phosphatase is best demonstrated with inhibitory regulatory mechanisms acting via nitric oxide. The second modification of the model incorporates cooperativity in cross-bridge attachment to predict improved data on the dependence of force on phosphorylation. The molecular basis for cooperativity is unknown, but may involve thin filament proteins absent in striated muscle.

Absence of force suppression in rabbit bladder correlates with low expression of heat shock protein 20

Background

Nitroglycerin can induce relaxation of swine carotid artery without sustained reductions in [Ca²⁺]_i or myosin regulatory light chain (MRLC) phosphorylation. This has been termed force suppression and been found to correlate with ser¹⁶-phosphorylation of heat shock protein 20 (HSP20). We tested for the existence of this mechanism in a smooth muscle that is not responsive to nitric oxide.

Methods

Isometrically mounted mucosa free rabbit bladder strips were contracted with carbachol and relaxed with 8-Br-cGMP, forskolin, or isoprenaline.

Results

Contraction was associated with a highly cooperative relation between MRLC phosphorylation and force such that very small increases in MRLC phosphorylation induced large increases in force. Relaxation induced by 8-Br-cGMP, forskolin, or isoprenaline did not shift the MRLC phosphorylation-force relation from that observed with carbachol alone, i.e. there was no force suppression. HSP20 content was negligible (approximately two hundred-fold less than swine carotid).

Conclusion

The lack of force suppression in the absence of HSP20 is consistent with the hypothesized role for HSP20 in the force suppression observed in tonic smooth muscles.

HSP20 phosphorylation and interstitial metabolites in hypoxia-induced dilation of swine coronary arteries

OBJECTIVE

Hypoxia induces coronary artery dilation, but the responsible mechanism is largely unknown. Many stimuli induce arterial smooth muscle relaxation by reducing ser19-myosin regulatory light chain (MLC) phosphorylation. Other stimuli can induce smooth muscle relaxation without reductions in ser19-MLC phosphorylation. This form of relaxation has been termed force suppression and appears to be associated with heat shock protein 20 (HSP20) phosphorylation on ser16. We investigated whether hypoxia-induced sustained dilation in swine coronary arteries was promoted without ser19-MLC dephosphorylation and associated with ser16-HSP20 phosphorylation. Nitroglycerin vasodilation served as control.

METHODS

In a pressure myograph, the tunica media of intact pre-contracted (PGF(2alpha); 10(-5) m) porcine coronary artery segments were cannulated using a microdialysis catheter. Diameter responses and interstitial lactate/pyruvate ratios were studied during 90 min hypoxia, hypoxia + reoxygenation (60 min), nitroglycerin (100 microm, 90 min), and nitroglycerin + wash-out (60 min). The arterial segments were snap-frozen and analysed for ser16-HSP20 phosphorylation and ser19-MLC phosphorylation.

RESULTS

The normalized diameter responses to hypoxia (6.1 +/- 4.3%) and nitroglycerin (12.6 +/- 1.6%) were both significantly greater than normoxic control arteries (-10.5 +/- 1.8%, anova, P < 0.05). Ser16-HSP20 phosphorylation was increased with hypoxia and nitroglycerin treatment and ser16-HSP20 phosphorylation correlated with changes in diameters (n = 29, r2 = 0.64, P < 0.001). Ser19-MLC phosphorylation was not significantly altered by hypoxia. The lactate/pyruvate ratio was significantly increased in hypoxic arteries but did not correlate with diameters or ser16-HSP20 phosphorylation.

CONCLUSION

Ser16-HSP20 phosphorylation is a potential regulator of hypoxia-induced dilation in coronary arteries.

Serine 68 phospholemman phosphorylation during forskolin-induced swine carotid artery relaxation

BACKGROUND

Phospholemman (PLM) is an abundant phosphoprotein in the plasma membrane of cardiac, skeletal and smooth muscle. It is a member of the FXYD family of proteins that bind to and regulate the Na,K-ATPase. Protein kinase A (PKA) is known to phosphorylate PLM on serine 68 (S68), although the functional effect of S68 PLM phosphorylation is unclear. We therefore evaluated S68 PLM phosphorylation in swine carotid arteries.

METHODS

Two anti-PLM antibodies, one to S68 phosphorylated PLM and one to unphosphorylated PLM, were made to PLM peptides in rabbits and tested with purified PLM and PKA-treated PLM. Swine carotid arteries were mounted isometrically, contracted, relaxed with forskolin and then homogenized. Proteins were separated on SDS gels and the intensity of immunoreactivity to the two PLM antibodies determined on immunoblots.

RESULTS

The antipeptide antibody 'C2' primarily reacted with unphosphorylated PLM, and the antipeptide antibody 'CP68' detected S68 PLM phosphorylation. Histamine stimulation of intact swine carotid artery induced a contraction, increased the CP68 PLM antibody signal and reduced the C2 PLM antibody signal. High extracellular [K(+)] depolarization induced a contraction without altering the C2 or CP68 PLM signal. Forskolin-induced relaxation of histamine or extracellular [K(+)] contracted arteries correlated with an increased CP68 signal. Nitroglycerin-induced relaxation was not associated with changes in the C2 or CP68 PLM signal.

CONCLUSIONS

These data suggest that a contractile agonist increased S68 PLM phosphorylation. Agents that increase [cAMP], but not agents that increase [cGMP], increased S68 PLM phosphorylation. S68 PLM phosphorylation may be involved in cAMP-dependent regulation of smooth muscle force.

Children with obstructive sleep-disordered breathing generate high-frequency inspiratory sounds during sleep

STUDY OBJECTIVES

We observed that some children with adenotonsillar hypertrophy and obstructive sleep-disordered breathing (SDB) make high-frequency inspiratory sounds (HFIS) during sleep. Our objective was to determine whether HFIS occur in most children with obstructive SDB and adenotonsillar hypertrophy and whether adenotonsillectomy reduces HFIS.

DESIGN

Prospective consecutive-entry trial.

SETTING

Sleep laboratory.

PARTICIPANTS

Twenty-six children between 6 and 12 years of age with adenotonsillar hypertrophy suspected of having obstructive SDB.

MEASUREMENTS AND RESULTS

We performed polysomnography and measured sounds during sleep with a microphone suspended above the bed. Sounds were recorded on a computer at 44 kHz, analyzed with fast Fourier transformation for frequency content. HFIS were sounds occurring during an inspiration with frequencies greater than 2 kHz. HFIS were different from the low-frequency (< 2 kHz) sounds described in snoring adults. HFIS usually occurred in consecutive breaths, occasionally exceeding 100. We counted the number of HFIS that occurred per hour of sleep. Children who made more HFIS had more obstructive SDB than did those who did not make the HFIS, and there was a significant positive correlation between the number of HFIS and the obstructive apnea-hypopnea index. Children with more than 3 apneas and hypopneas per hour of sleep all made at least 10 HFIS per hour, and all children who had more than 10 HFIS per hour had obstructive apnea-hypopnea index values greater than 1. Children with adenotonsillar hypertrophy made more HFIS than did those children whose tonsils and adenoids had been removed.

CONCLUSIONS

HFIS may be a marker of disturbed breathing during sleep in children with adenotonsillar hypertrophy.

An upper airway resonator model of high-frequency inspiratory sounds in children with sleep-disordered breathing

The goal of this study was to determine how high-frequency inspiratory sounds (HFIS) are generated by sleeping children with obstructive sleep-disordered breathing (OSDB). We hypothesized that HFIS are generated when a high-velocity jet of air, generated by a narrowed upper airway, induces the upper airway to act as a resonating chamber. We tested two predictions of this hypothesis: 1) the upper airway is narrowed in children who make HFIS and 2) the length of the upper airway, calculated from HFIS harmonic intervals, is similar to that calculated from magnetic resonance imaging (MRI) scans. The study was conducted in the setting of a sleep laboratory. Participants included 29 children between 6 and 12 yr of age with adenotonsillar hypertrophy suspected of having OSDB. Minimum cross-sectional airway area and airway long dimensions (lips to larynx or soft palate) were measured in awake children with MRIs. Later that night, sound was recorded with a microphone suspended above their bed while the children underwent polysomnography. Sounds were later analyzed with fast Fourier transforms. We found that sleeping children who generated HFIS had significantly narrower upper airways compared with children who did not make HFIS [minimum airway area 20.5 +/- 4.4 vs. 70.9 +/- 22.5 mm(2) (mean +/- SE), respectively; P = 0.02]. There was a significant inverse correlation between the log(10) of the narrowest airway area and the number of HFIS recorded per hour (r(2) = 0.55, P < 0.00001). The harmonics characteristics of HFIS predicted that they were generated by sound resonating in chamber whose length was 12.0 +/- 0.9 cm, which is similar to the MRI measured distance from the lips to the larynx of 12.8 +/- 0.4 cm. In conclusion, these data suggest that children generate HFIS when 1) they have a narrowed upper airway and 2) their upper airway acts as a resonating chamber.

Heat shock protein 20-mediated force suppression in forskolin-relaxed swine carotid artery

Increases in cyclic nucleotide levels induce smooth muscle relaxation by deactivation [reductions in myosin regulatory light chain (MRLC) phosphorylation (e.g., by reduced [Ca(2+)])] or force suppression (reduction in force without reduction in MRLC phosphorylation). Ser(16)-heat shock protein 20 (HSP20) phosphorylation is the proposed mediator of force suppression. We evaluated three potential hypotheses whereby Ser(16)-HSP20 phosphorylation could regulate smooth muscle force: 1) a threshold level of HSP20 phosphorylation could inactivate a thin filament as a whole, 2) phosphorylation of a single HSP20 could fully inactivate a small region of a thin filament, or 3) HSP20 phosphorylation could weakly inhibit myosin binding at either the thin- or thick-filament level. We tested these hypotheses by analyzing the dependence of force on Ser(16)-HSP20 phosphorylation in swine carotid media. First, we determined that swine HSP20 has a second phosphorylation site at Ser(157). Ser(157)-HSP20 phosphorylation values were high and did not change during contractile activation or forskolin-induced relaxation. Forskolin significantly increased Ser(16)-HSP20 phosphorylation. The relationship between Ser(16)-HSP20 phosphorylation and force remained linear and was shifted downward in partially activated muscles relaxed with forskolin. Neither forskolin nor nitroglycerin induced actin depolymerization as detected using the F/G-actin ratio method in smooth muscle homogenates. These results suggest that force suppression does not occur in accordance with the first hypothesis (inactivation of a thin filament as a whole). Our data are more consistent with the second and third hypotheses that force suppression is mediated by full or partial inhibition of local myosin binding at the thin- or thick-filament level.

Combination therapy of dyslipidemia in non-insulin-dependent diabetes mellitus and the metabolic syndrome

Non-insulin-dependent diabetes mellitus (NIDDM) and the metabolic syndrome separately and additively increase the risk for atherosclerotic cardiovascular disease. Considering the high cardiovascular risk associated with NIDDM and the metabolic syndrome, aggressive therapy of dyslipidemia with tailored combination therapy should be considered given informed consent and discussion of risks. In addition to statins, niacin, and fibrates, therapies shown to decrease the risk for atherosclerotic cardiovascular disease include omega-3 fatty acids, diet, exercise, and optimal blood pressure control with thiazides and blockers of the renin-angiotensin system. These therapies should also be considered to reduce the high cardiovascular risk associated with NIDDM and the metabolic syndrome.

Cooperative attachment of cross bridges predicts regulation of smooth muscle force by myosin phosphorylation

Serine 19 phosphorylation of the myosin regulatory light chain (MRLC) appears to be the primary determinant of smooth muscle force development. The relationship between MRLC phosphorylation and force is nonlinear, showing that phosphorylation is not a simple switch regulating the number of cycling cross bridges. We reexamined the MRLC phosphorylation-force relationship in slow, tonic swine carotid media; fast, phasic rabbit urinary bladder detrusor; and very fast, tonic rat anococcygeus. We found a sigmoidal dependence of force on MRLC phosphorylation in all three tissues with a threshold for force development of approximately 0.15 mol P(i)/mol MRLC. This behavior suggests that force is regulated in a highly cooperative manner. We then determined whether a model that employs both the latch-bridge hypothesis and cooperative activation could reproduce the relationship between Ser(19)-MRLC phosphorylation and force without the need for a second regulatory system. We based this model on skeletal muscle in which attached cross bridges cooperatively activate thin filaments to facilitate cross-bridge attachment. We found that such a model describes both the steady-state and time-course relationship between Ser(19)-MRLC phosphorylation and force. The model required both cooperative activation and latch-bridge formation to predict force. The best fit of the model occurred when binding of a cross bridge cooperatively activated seven myosin binding sites on the thin filament. This result suggests cooperative mechanisms analogous to skeletal muscle that will require testing.

Heat induced HSP20 phosphorylation without increased cyclic nucleotide levels in swine carotid media

BACKGROUND

Heat pretreatment of swine carotid artery has been shown to increase ser16-heat shock protein 20 (HSP20) phosphorylation and suppress force, i.e., reduce force with only minimal reduction in ser19-myosin regulatory light chain (MRLC) phosphorylation.

RESULTS

We further investigated this response in intact histamine stimulated swine carotid artery rings. There was a heat threshold such that increased ser16-HSP20 phosphorylation and force suppression were observed between 43 degrees C and 46 degrees C. The increased ser16-HSP20 phosphorylation persisted up to 16 hours after 44.5 degrees C heat treatment. Pretreatment of swine carotid media at 44.5 degrees C increased ser16-HSP20 phosphorylation without increases in [cAMP] or [cGMP], suggesting an alternate mechanism, perhaps phosphatase inhibition, for the increase in ser16-HSP20 phosphorylation. Heat pretreatment at 47.5 degrees C reduced force by decreasing MRLC phosphorylation rather than by large increases in ser16-HSP20 phosphorylation. HSP20 phosphorylation at the putative PKC site did not change with any treatment.

CONCLUSION

These results demonstrate that multiple mechanisms can induce force suppression that is correlated with ser16-HSP20 phosphorylation: 1) nitrovasodilators via cGMP, 2) forskolin via cAMP, and 2) thermal stress in a cyclic nucleotide independent manner.

Oral L-arginine can reverse digital necrosis in Raynaud's phenomenon

Raynaud's phenomenon is characterized by transient reduction in blood supply through the small arteries in the hands and feet. Severe Raynaud's phenomenon can cause digital necrosis. It has been hypothesized that nitric oxide may have a role in Raynaud's phenomenon. We report two cases in which oral L-arginine reversed digital necrosis in Raynaud's phenomenon and two additional cases in which the symptoms of severe Raynaud's phenomenon were improved with oral L-arginine. These reports suggest that a defect in nitric oxide synthesis or metabolism is present in Raynaud's phenomenon. They also suggest a potential role for oral L-arginine therapy in Raynaud's phenomenon, especially in Raynaud's phenomenon with digital necrosis.

Heat-induced force suppression and HSP20 phosphorylation in swine carotid media

In vascular smooth muscle, cyclic nucleotide-dependent phosphorylation of heat shock protein 20 (HSP20) on serine-16 (Ser16) has been suggested to cause force suppression, i.e., reduced force with only minimal myosin regulatory light chain (MRLC) dephosphorylation. We hypothesized that heat pretreatment also suppresses force by increasing HSP20 phosphorylation. After heat pretreatment of swine carotid artery at 44.5 degrees C for 4 h and reduction to 37 degrees C for 1 h, Ser16-HSP20 phosphorylation was increased and histamine-induced increases in contractile force were suppressed. Subsequent addition of nitroglycerin induced additive force suppression. Heat and nitroglycerin induced a similar relation between Ser16-HSP20 phosphorylation and force. Heat pretreatment induced a small, but significant, increase in total HSP20 immunostaining. These results demonstrate that vascular smooth muscle responds to thermal stress by increasing Ser16-HSP20 phosphorylation in addition to a possible small increase in total HSP20 concentration. The resulting heat-induced reduction in force should be considered "force suppression" because histamine-induced increases in MRLC phosphorylation were not significantly altered by heat pretreatment. These processes may bring about a resistance to contractile agonists, which could have clinical significance in conditions such as hyperthermia and/or sepsis with vasodilatory shock.

Selected contribution: HSP20 phosphorylation in nitroglycerin- and forskolin-induced sustained reductions in swine carotid media tone

Cyclic nucleotide-induced relaxation of maximally activated arterial smooth muscle has two phases. 1) The initial relaxation transient is typically characterized by a rapid reduction in force associated with brief reductions in myoplasmic Ca(2+) concentration ([Ca(2+)](i)) and myosin regulatory light chain (MRLC) phosphorylation on serine (Ser)-19 (Ser(19)). 2) The sustained inhibitory response is typically associated with Ser(16) phosphorylation of heat shock protein 20 (HSP20) without sustained reductions in [Ca(2+)](i) or MRLC phosphorylation. We investigated whether the extent of Ser(16)-HSP20 phosphorylation quantitatively correlated with the sustained inhibitory response. With addition of nitroglycerin to histamine-stimulated swine carotid media, the initial relaxation transient was associated with a decrease in MRLC phosphorylation without an increase in Ser(16)-HSP20 phosphorylation. During the sustained phase of nitroglycerin-induced relaxation and during force redevelopment induced by washout of nitroglycerin in the continued presence of histamine, the level of Ser(16)-HSP20 phosphorylation, but not MRLC phosphorylation, correlated with inhibition of force. Forskolin, which increases cAMP concentration, also induced a sustained inhibitory response that was associated with increases in Ser(16)-HSP20 phosphorylation without reductions in MRLC phosphorylation levels. Forskolin increased Ser(16)-HSP20 phosphorylation to a greater extent and inhibited force more completely than that observed with nitroglycerin. Increases in Ser(16)-HSP20 phosphorylation correlated with the degree of force inhibition regardless of whether the relaxation was induced by nitroglycerin or forskolin. These data are consistent with the hypothesis that Ser(16)-HSP20 phosphorylation may be a cyclic nucleotide-dependent, yet MRLC phosphorylation-independent, inhibitor of smooth muscle contractile force.

Localization of heat shock protein 20 in swine carotid artery

BACKGROUND

Cyclic nucleotides can relax vascular smooth muscle by mechanisms distal to myosin regulatory light chain (MRLC) phosphorylation. This mechanism, termed relaxation without MRLC dephosphorylation, may be regulated by ser16 phosphorylation of heat shock protein 20 (HSP20).

RESULTS

Confocal imaging of HSP20 in smooth muscle tissues revealed that HSP20 was present throughout the cytoplasm, although some focal regions of the cytoplasm were found to contain more HSP20 than the remaining cytoplasm. The distribution of HSP20 within the cytoplasm was not altered by histamine, forskolin, or nitroglycerin.

CONCLUSION

Cytoplasmic localization of HSP20 is consistent with a potential function of HSP20 as a regulator of smooth muscle contractile force.

cGMP-mediated phosphorylation of heat shock protein 20 may cause smooth muscle relaxation without myosin light chain dephosphorylation in swine carotid artery

Nitrovasodilators such as nitroglycerine, via production of nitric oxide and an increase in [cGMP], can induce arterial smooth muscle relaxation without proportional reduction in myosin light chain (MLC) phosphorylation or myoplasmic [Ca2+]. These findings suggest that regulatory systems, other than MLC phosphorylation and Ca2+, partially mediate nitroglycerine-induced relaxation. In swine carotid artery, we found that a membrane-permeant cGMP analogue induced relaxation without MLC dephosphorylation, suggesting that cGMP mediated the relaxation. Nitroglycerine-induced relaxation was associated with a reduction in O2 consumption, suggesting that the interaction between phosphorylated myosin and the thin filament was inhibited. Nitroglycerine-induced relaxation was associated with a 10-fold increase in the phosphorylation of a protein on Ser16. We identified this protein as heat shock protein 20 (HSP20), a member of a family of proteins known to bind to thin filaments. When homogenates of nitroglycerine-relaxed tissues were centrifuged at 6000 g, phosphorylated HSP20 preferentially sedimented in the pellet, suggesting that phosphorylation of HSP20 may increase its affinity for the thin filament. We noted that a domain of HSP20 is partially homologous to the 'minimum inhibitory sequence' of skeletal troponin I. The peptide HSP20110-121, which contains this domain, bound to actin-containing filaments only in the presence of tropomyosin, a characteristic of troponin I. High concentrations of HSP20110-121 abolished Ca2+-activated force in skinned swine carotid artery. HSP20110-121 also partially decreased actin-activated myosin S1 ATPase activity. These data suggest that cGMP-mediated phosphorylation of HSP20 on Ser16 may have a role in smooth muscle relaxation without MLC dephosphorylation. HSP20 contains an actin-binding sequence at amino acid residues 110-121 that inhibited force production in skinned carotid artery. We hypothesize that phosphorylation of HSP20 regulates force independent of MLC phosphorylation via binding of HSP20 to thin filaments and inhibition of cross-bridge cycling.

Caldesmon and heat shock protein 20 phosphorylation in nitroglycerin- and magnesium-induced relaxation of swine carotid artery

Nitrovasodilators, high extracellular Mg(2+), and some other relaxing agents can cause smooth muscle relaxation without reductions in myosin regulatory light chain (MRLC) phosphorylation. Relaxations without MRLC dephosphorylation suggest that other regulatory systems, beyond MRLC phosphorylation, are present in smooth muscle. We tested whether changes in caldesmon phosphorylation, heat shock protein 20 (HSP20) phosphorylation, or intracellular pH (pH(i)) could be responsible for relaxation without MRLC dephosphorylation. In unstimulated tissues, caldesmon was phosphorylated 1.02+/-0.10 mol P(i)/mol caldesmon (mean+/-1 S.E.M.), HSP20 was phosphorylated 0.005+/-0.003 mol P(i)/mol HSP20, and estimated pH(i) was 7.21+/-0.07. Histamine stimulation induced a contraction, an intracellular acidosis, but did not significantly change caldesmon or HSP20 phosphorylation. Addition of nitroglycerin induced a relaxation, significantly increased HSP20 phosphorylation to 0.18+/-0.02 mol P(i)/mol HSP20, did not significantly change caldesmon phosphorylation, and pH(i) returned to near unstimulated values. Increase in extracellular Mg(2+) to 10 mM induced a relaxation, but did not significantly change HSP20 or caldesmon phosphorylation. These data suggest that changes in caldesmon phosphorylation, HSP20 phosphorylation, or pH(i) cannot be the sole explanation for relaxation without MRLC dephosphorylation. However, it is possible that HSP20 phosphorylation may be involved in nitroglycerin-induced relaxation without MRLC dephosphorylation.

The buffer barrier hypothesis, [Ca2+]i homogeneity, and sarcoplasmic reticulum function in swine carotid artery

1. The goal of this study was to evaluate the buffer barrier hypothesis in an intact arterial smooth muscle. Specifically, we investigated the interrelationships between intracellular [Ca2+] ([Ca2+]i) homogeneity and sarcoplasmic reticulum function in swine carotid artery. 2. We measured focal changes in [Ca2+]i by exploiting the different characteristics of several [Ca2+]i indicators: (1) aequorin, which can detect focal increases in [Ca2+]i such as those that occur in the subplasmalemmal region ([Ca2+]pm); (2) fura-2, which is primarily a measure of mean cytoplasmic [Ca2+] ([Ca2+]c); and (3) force, which reflects increases in [Ca2+] near the contractile apparatus. We then estimated the relative degree of [Ca2+]i homogeneity with the aequorin/fura-2 ratio. Finally, we inhibited sarcoplasmic reticulum Ca2+ pumping with cyclopiazonic acid (CPA), an inhibitor of the sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA). 3. We found that, after Ca2+ depletion, the sarcoplasmic reticulum could be partially reloaded with Ca2+ by manipulations that increased the aequorin signal relatively more than the fura-2 signal. Complete reloading required large increases in the fura-2 signal. These data suggest that increases in [Ca2+]pm (as measured with aequorin) can partially reload the sarcoplasmic reticulum, but complete reloading required increases in [Ca2+]c (as measured with fura-2). Reloading could be partially inhibited by 10 microM CPA, indicating that SERCA function was important for reloading. 4. In unstimulated arteries, 10 microM CPA increased the fura-2 signal without altering the aequorin signal, thereby decreasing the aequorin/fura-2 ratio. Removal of extracellular Ca2+ without CPA also reduced the aequorin/fura-2 ratio. These data suggest that resting cells have a [Ca2+] gradient with [Ca2+]pm > [Ca2+]c; this gradient is maintained by SERCA function. 5. CPA slowed the decline in the fura-2 signal observed when histamine stimulation was removed. This result is consistent with the concept of vectorial Ca2+ efflux in which Ca2+ pumping by SERCA reduces [Ca2+]c after stimulation. 6. Ca2+ depletion by prior treatment with 100 microM histamine and CPA transiently attenuated subsequent histamine-induced aequorin and fura-2 transients. The effect on contraction was smaller: a delay in contraction of approximately 10 s. These data suggest that histamine-induced Ca2+ release has at least a small role in the initial phase of contraction; however, other contractile mechanisms appear to be able to compensate for loss of Ca2+ release with only modest changes in contraction kinetics. 7. These data suggest that there is a complex interrelationship between smooth muscle sarcoplasmic reticulum function and [Ca2+] in at least two cytoplasmic compartments. [Ca2+]pm and [Ca2+]c can differentially regulate sarcoplasmic reticulum Ca2+ filling; and sarcoplasmic reticulum function regulates [Ca2+]pm and [Ca2+]c.

Number needed to screen: development of a statistic for disease screening

OBJECTIVES

To develop the number needed to screen, a new statistic to overcome inappropriate national strategies for disease screening. Number needed to screen is defined as the number of people that need to be screened for a given duration to prevent one death or adverse event.

DESIGN

Number needed to screen was calculated from clinical trials that directly measured the effect of a screening strategy. From clinical trials that measured treatment benefit, the number needed to screen was estimated as the number needed to treat from the trial divided by the prevalence of heretofore unrecognised or untreated disease. Directly calculated values were then compared with estimate number needed to screen values.

SUBJECTS

Standard literature review.

RESULTS

For prevention of total mortality the most effective screening test was a lipid profile. The estimated number needed to screen for dyslipidaemia (low density lipoprotein cholesterol concentration >4.14 mmol/1) was 418 if detection was followed by pravastatin treatment for 5 years. This indicates that one death in 5 years could be prevented by screening 418 people. The estimated number needed to screen for hypertension was between 274 and 1307 for 5 years (for 10 mm Hg and 6 mm Hg diastolic blood pressure reduction respectively) if detection was followed by treatment based on a diuretic. Screening with haemoccult testing and mammography significantly decreased cancer specific, but not total, mortality. The number needed to screen for haemoccult screening to prevent a death from colon cancer was 1374 for 5 years, and the number needed to screen for mammography to prevent a death from breast cancer was 2451 for 5 years for women aged 50-59.

CONCLUSION

These data allow the clinician to prioritise screening strategies. Of the screening strategies evaluated, screening for, and treatment of, dyslipidaemia and hypertension seem to produce the largest clinical benefit.

Imaging bioluminescent indicators shows Ca2+ and ATP permeability thresholds in live cells attacked by complement

A series of permeability thresholds to Ca2+ metabolites and macromolecules, occurring at different times when cells are attacked by complement, has been established by imaging HeLa cells transiently expressing a recombinant cytosolic fusion protein of firefly luciferase and aequorin (luciferase-aequorin) to measure changes in ATP and cytosolic free Ca2+. Nuclear fluorescence of propidium was used as a measure of permeability to small molecules, and luciferase activity imaged to assess lysis. The rise in cytosolic free Ca2+ observed after C9 attack preceded by at least 60 s both the increase in propidium fluorescence, measured in single cells, and the decrease in ATP monitored by luciferase light emission. These effects were dependent on the concentration of C9. At concentrations of C9 up to 4 micrograms/ml no loss of luciferase-aequorin protein was detected at the end of the experiment. Thus the membrane integrity of the cells remained intact, even though the cells were permeable to propidium. These results confirmed our earlier observations that propidium permeability in cells attacked by complement was not a reliable measure of cell death. They also show that it is vital to take account of cellular heterogeneity if the mechanisms by which cells respond to membrane pore former attack are to be correctly interpreted.