Harold A. Spurgeon

Elevated Aortic Pulse Wave Velocity, a Marker of Arterial Stiffness, Predicts Cardiovascular Events in Well-Functioning Older Adults

Background—Aging results in vascular stiffening and an increase in the velocity of the pressure wave as it travels down the aorta. Increased aortic pulse wave velocity (aPWV) has been associated with mortality in clinical but not general populations. The objective of this investigation was to determine whether aPWV is associated with total and cardiovascular (CV) mortality and CV events in a community-dwelling sample of older adults. Methods and Results—aPWV was measured at baseline in 2488 participants from the Health, Aging and Body Composition (Health ABC) study. Vital status, cause of death and coronary heart disease (CHD), stroke, and congestive heart failure were determined from medical records. Over 4.6 years, 265 deaths occurred, 111 as a result of cardiovascular causes. There were 341 CHD events, 94 stroke events, and 181 cases of congestive heart failure. Results are presented by quartiles because of a threshold effect between the first and second aPWV quartiles. Higher aPWV was associated with both total mortality (relative risk, 1.5, 1.6, and 1.7 for aPWV quartiles 2, 3, and 4 versus 1; P=0.019) and cardiovascular mortality (relative risk, 2.1, 3.0, and 2.3 for quartiles 2, 3, and 4 versus 1; P=0.004). aPWV quartile was also significantly associated with CHD (P=0.007) and stroke (P=0.001). These associations remained after adjustment for age, gender, race, systolic blood pressure, known CV disease, and other variables related to events. Conclusions—Among generally healthy, community-dwelling older adults, aPWV, a marker of arterial stiffness, is associated with higher CV mortality, CHD, and stroke.

8-bromo-cGMP reduces the myofilament response to Ca2+ in intact cardiac myocytes.

The role of cGMP in myocardial contraction is not established. Recent reports suggest that nitric oxide, released by endothelial cells or within myocytes, modifies myocardial contraction by raising cGMP. We studied the effects of 8-bromo-cGMP (8bcGMP, 50 mumol/L) on contraction (cell shortening) and simultaneous intracellular Ca2+ transients (indo 1 fluorescence ratio) in intact adult rat ventricular myocytes (0.5 Hz and 25 degrees C) 8bcGMP reduced myocyte twitch amplitude and time to peak shortening (-19.6 +/- 4.2% and -17.6 +/- 1.3%, respectively) and increased steady-state diastolic cell length (+0.6 +/- 0.1 microns, mean +/- SEM, n = 8; all P < .05) but had no effect on shortening velocity, systolic or diastolic fluorescence ratio, or time to peak fluorescence ratio (all P = NS). In 7 of 13 myocytes, this negative inotropic effect was preceded by a transient positive inotropic effect, with small increases in twitch amplitude, shortening velocity, and cytosolic Ca2+ transient. Analysis of 8bcGMP effects on both the dynamic and steady-state relation between cell shortening and intracellular Ca2+ (during twitch contraction and tetanic contraction, respectively) indicated reduction in the myofilament response to Ca2+ in all cases. These 8bcGMP effects were inhibited by KT5823 (1 mumol/L), an inhibitor of cGMP-dependent protein kinase, or by the presence of isoproterenol (3 nmol/L). 8bcGMP had no effect on cytosolic pH in cells (n = 4) loaded with the fluorescent probe carboxyseminaphthorhodafluor-1. These data indicate that cGMP may modulate myocardial relaxation and diastolic tone by reducing the relative myofilament response to Ca2+, probably via cGMP-dependent protein kinase.

CENTRAL OR PERIPHERAL SYSTOLIC OR PULSE PRESSURE: WHICH BEST RELATES TO TARGET-ORGANS AND FUTURE MORTALITY?

Objective To examine the relationship between brachial and central carotid pressures and target organ indices at baseline and their association with future mortality. Methods We examined, cross-sectionally and longitudinally, the relations of baseline systolic and pulse pressures in central (calibrated tonometric carotid pulse) and peripheral (brachial, mercury sphygmomanometer) arteries to baseline left ventricular mass, carotid intima-media thickness, estimated glomerular filtration rate, and 10-year all-cause and cardiovascular mortality in 1272 participants (47% women aged 30–79 years) from a community of homogeneous Chinese. Results Left ventricular mass was more strongly related to central and peripheral systolic pressures than pulse pressures. Intima-media thickness and glomerular filtration rate were more strongly related to central pressures than peripheral pressures. A total of 130 participants died, 37 from cardiovascular causes. In univariate analysis, all four blood pressure variables significantly predicted all-cause and cardiovascular mortality. Each blood pressure variable was entered into the multivariate models, both individually and jointly with another blood pressure variable. After adjustment for age, sex, heart rate, BMI, current smoking, glucose, ratio of total cholesterol to high-density lipoprotein cholesterol, carotid–femoral pulse wave velocity, left ventricular mass, intima-media thickness, and glomerular filtration rate, only central systolic pressure consistently and independently predicted cardiovascular mortality (hazards ratio, 1.30 per 10 mmHg). No significant sex interactions were observed in all analyses. Conclusion Systolic and pulse pressures relate differently to different target organs. Central systolic pressure is more valuable than other blood pressure variables in predicting cardiovascular mortality.

Wave reflection and arterial stiffness in the prediction of 15-year all-cause and cardiovascular mortalities: a community-based study.

The value of increased arterial wave reflection, usually assessed by the transit time–dependent augmentation index and augmented pressure (Pa), in the prediction of cardiovascular events may have been underestimated. We investigated whether the transit time–independent measures of reflected wave magnitude predict cardiovascular outcomes independent of arterial stiffness indexed by carotid-femoral pulse wave velocity. A total of 1272 participants (47% women; mean age: 52±13 years; range: 30 to 79 years) from a community-based survey were studied. Carotid pressure waveforms derived by tonometry were decomposed into their forward wave amplitudes, backward wave amplitudes (Pb), and a reflection index (=[Pb/(forward wave amplitude+Pb)]), in addition to augmentation index, Pa, and reflected wave transit time. During a median follow-up of 15 years, 225 deaths occurred (17.6%), including 64 cardiovascular origins (5%). In univariate Cox proportional hazard regression analysis, pulse wave velocity, Pa, and Pb predicted all-cause and cardiovascular mortality in both men and women, whereas augmentation index, reflected wave transit time, and reflection index were predictive only in men. In multivariate analysis accounting for age, height, and heart rate, Pb predicted cardiovascular mortality in both men and women, whereas Pa was predictive only in men. Per 1-SD increment (6 mm Hg), Pb predicted 15-year cardiovascular mortality independent of brachial but not central pressure, pulse wave velocity, augmentation index, Pa, and conventional cardiovascular risk factors with hazard ratios of ≈1.60 (all P<0.05). In conclusion, Pb, a transit time–independent measure of reflected wave magnitude, predicted long-term cardiovascular mortality in men and women independent of arterial stiffness.

Correlates of aortic stiffness in elderly individuals: A subgroup of the Cardiovascular Health Study

BACKGROUND Arterial stiffness has been associated with aging, hypertension, and diabetes; however, little data has been published examining risk factors associated with arterial stiffness in elderly individuals. METHODS Longitudinal associations were made between aortic stiffness and risk factors measured approximately 4 years earlier. Aortic pulse wave velocity (PWV), an established index of arterial stiffness, was measured in 356 participants (53.4% women, 25.3% African American), aged 70 to 96 years, from the Pittsburgh site of the Cardiovascular Health Study during 1996 to 1998. RESULTS Mean aortic pulse wave velocity (850 cm/sec, range 365 to 1863) did not differ by ethnicity or sex. Increased aortic stiffness was positively associated with higher systolic blood pressure (SBP), age, fasting and 2-h postload glucose, fasting and 2-h insulin, triglycerides, waist circumference, body mass index, truncal fat, decreased physical activity, heart rate, and common carotid artery wall thickness (P < .05). After controlling for age and SBP, the strongest predictors of aortic stiffness in men were heart rate (P = .001) and 2-h glucose (P = .063). In women, PWV was positively associated with heart rate (P = .018), use of antihypertensive medication (P = .035), waist circumference (P = .030), and triglycerides (P = .081), and was negatively associated with physical activity (P = .111). Results were similar when the analysis was repeated in nondiabetic individuals and in those free of clinical or subclinical cardiovascular disease in 1992 to 1993. CONCLUSIONS In these elderly participants, aortic stiffness was positively associated with risk factors associated with the insulin resistance syndrome, increased common carotid intima-media thickness, heart rate, and decreased physical activity measured several years earlier.

Kappa and delta opioid receptor stimulation affects cardiac myocyte function and Ca2+ release from an intracellular pool in myocytes and neurons.

We investigated the effects of mu, delta, and kappa opioid receptor stimulation on the contractile properties and cytosolic Ca2+ (Cai) of adult rat left ventricular myocytes. Cells were field-stimulated at 1 Hz in 1.5 mM bathing Ca2+ at 23 degrees C. The mu-agonist [D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin (10(-5) M) had no effect on the twitch. The delta-agonists methionine enkephalin and leucine enkephalin (10(-10) to 10(-6) M) and the kappa-agonist (trans-(dl)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclo-hexyl]- benzeneacetamide)methanesulfonate hydrate (U-50,488H; 10(-7) to 2 x 10(-5) M) had a concentration-dependent negative inotropic action. The sustained decrease in twitch amplitude due to U-50,488H was preceded by a transient increase in contraction. The effects of delta- and kappa-receptor stimulation were antagonized by naloxone and (-)-N-(3-furyl-methyl)-alpha-normetazocine methanesulfonate, respectively. In myocytes loaded with the Ca2+ probe indo-1, the effects of leucine enkephalin (10(-8) M) and U-50,488H (10(-5) M) on the twitch were associated with similar directional changes in the Cai transient. Myofilament responsiveness to Ca2+ was assessed by the relation between twitch amplitude and systolic indo-1 transient. Leucine enkephalin (10(-8) M) had no effect, whereas U-50,488H (10(-5) M) increased myofilament responsiveness to Ca2+. We subsequently tested the hypothesis that delta and kappa opioid receptor stimulation may cause sarcoplasmic reticulum Ca2+ depletion. The sarcoplasmic reticulum Ca2+ content in myocytes and in a caffeine-sensitive intracellular Ca2+ store in neurons was probed in the absence of electrical stimulation via the rapid addition of a high concentration of caffeine from a patch pipette above the cell. U-50,488H and leucine enkephalin slowly increased Cai or caused Cai oscillations and eventually abolished the caffeine-triggered Cai transient. These effects occurred in both myocytes and neuroblastoma-2a cells. In cardiac myocyte suspensions U-50,488H and leucine enkephalin both caused a rapid and sustained increase in inositol 1,4,5-trisphosphate. Thus, delta and kappa but not mu opioids have a negative inotropic action due to a decreased Cai transient. The decreased twitch amplitude due to kappa-receptor stimulation is preceded by a transient increase in contractility, and it occurs despite an enhanced myofilament responsiveness to Ca2+. The effects of delta and kappa opioids appear coupled to phosphatidylinositol turnover and, at least in part, may be due to sarcoplasmic reticulum Ca2+ depletion.(ABSTRACT TRUNCATED AT 400 WORDS)

Excitation-contraction coupling in heart: new insights from Ca2+ sparks

Ca2+ sparks, the elementary units of sarcoplasmic reticulum (SR) Ca2+ release in cardiac, smooth and skeletal muscle are localized (2-4 microns ) increases in intracellular Ca2+ concentration, [Ca2+]i, that last briefly (30-100 ms). These Ca2+ sparks arise from the openings of a single SR Ca2+ release channel (ryanodine receptor, RyR) or a few RyRs acting in concert. In heart muscle, Ca2+ sparks can occur spontaneously in quiescent cells at a low rate (100 s-1 per cell). Identical Ca2+ sparks are also triggered by depolarization because the voltage-gated sarcolemmal L-type Ca2+ channels (dihydropyridine receptors, DHPRs) locally increase [Ca2+]i and thereby activate the RyRs by Ca(2+)-induced Ca2+ release (CICR). The exquisite responsiveness of this process, reflected by the ability of even a single DHPR to activate a Ca2+ spark, is perhaps due to the large local increase in [Ca2+]i in the vicinity of the RyR that is a consequence of the close apposition of the DHPRs and the RyRs. In this review we examine our current understanding of cardiac excitation-contraction (EC) coupling in light of recent studies on the elementary Ca2+ release events or Ca2+ sparks. In addition, we further characterized Ca2+ spark properties in rat and mouse heart cells. Specifically we have determined that: (i) Ca2+ sparks occur at the junctions between the transverse-tubules and the SR in both species; (ii) Ca2+ sparks are asymmetric, being 18% longer in the longitudinal direction than in the transverse direction; and (iii) Ca2+ sparks individually do not produce measurable sarcomere shortening (< 1%). These results are discussed with respect to local activation of the RyRs, the stability of CICR, Ca2+ diffusion, and the theory of EC coupling.

Gi-Dependent Localization of β2-Adrenergic Receptor Signaling to L-Type Ca2+ Channels

A plausible determinant of the specificity of receptor signaling is the cellular compartment over which the signal is broadcast. In rat heart, stimulation of beta(1)-adrenergic receptor (beta(1)-AR), coupled to G(s)-protein, or beta(2)-AR, coupled to G(s)- and G(i)-proteins, both increase L-type Ca(2+) current, causing enhanced contractile strength. But only beta(1)-AR stimulation increases the phosphorylation of phospholamban, troponin-I, and C-protein, causing accelerated muscle relaxation and reduced myofilament sensitivity to Ca(2+). beta(2)-AR stimulation does not affect any of these intracellular proteins. We hypothesized that beta(2)-AR signaling might be localized to the cell membrane. Thus we examined the spatial range and characteristics of beta(1)-AR and beta(2)-AR signaling on their common effector, L-type Ca(2+) channels. Using the cell-attached patch-clamp technique, we show that stimulation of beta(1)-AR or beta(2)-AR in the patch membrane, by adding agonist into patch pipette, both activated the channels in the patch. But when the agonist was applied to the membrane outside the patch pipette, only beta(1)-AR stimulation activated the channels. Thus, beta(1)-AR signaling to the channels is diffusive through cytosol, whereas beta(2)-AR signaling is localized to the cell membrane. Furthermore, activation of G(i) is essential to the localization of beta(2)-AR signaling because in pertussis toxin-treated cells, beta(2)-AR signaling becomes diffusive. Our results suggest that the dual coupling of beta(2)-AR to both G(s)- and G(i)-proteins leads to a highly localized beta(2)-AR signaling pathway to modulate sarcolemmal L-type Ca(2+) channels in rat ventricular myocytes.

Phorbol ester and dioctanoylglycerol stimulate membrane association of protein kinase C and have a negative inotropic effect mediated by changes in cytosolic Ca2+ in adult rat cardiac myocytes.

We used left ventricular myocytes from adult rats to investigate the effect of 4 beta-phorbol 12-myristate 13-acetate (PMA) and of sn-1,2-dioctanoylglycerol (DiC-8) on the membrane association of protein kinase C (PKC), cytosolic [Ca2+], (Cai) homeostasis, and the contractile properties of single cardiac cells. Because PKC activity is known to be highly Ca2+ sensitive, the K+ concentration of the bathing medium was raised from 5 to 30 mM in some experiments, a perturbation known to depolarize the cell and increase Cai. In cell suspensions both PMA (3 x 10(-10) and 3 x 10(-7) M) and DiC-8 (10(-5) and 10(-4) M) increased membrane association of PKC. The effect of PMA (10(-7) M) on PKC translocation was enhanced in 30 mM KCl compared with 5 mM KCl. During steady field stimulation at 1 Hz in 1 mM bathing [Ca2+], both PMA (10(-7) M) and DiC-8 (10(-5) M) decreased twitch amplitude to approximately 60% of control in 5 mM KCl, and the negative inotropic effect of either drug was more pronounced in 30 mM KCl than in 5 mM KCl. In single cardiac myocytes loaded with the Ca2+ indicator indo-1 and bathed in 5 mM KCl, we simultaneously measured cell length and Cai. The myofilament responsiveness to Ca2+ was assessed by the relation between contraction amplitude and the peak of the Cai transient. The negative inotropic effect of both PMA and DiC-8 was related to a diminished amplitude of the Cai transient and not to a decreased myofilament responsiveness to Ca2+. In the absence of electrical stimulation, PMA (10(-7) M) and DiC-8 (10(-5) M) decreased the frequency of contractile waves due to spontaneous Ca2+ release from the sarcoplasmic reticulum, and DiC-8 also decreased resting Cai. Thus, activation of PKC, which is thought to occur as part of the response of cardiac muscle to alpha 1-adrenergic stimulation, is associated with a negative inotropic action due to a smaller Cai transient rather than to a decrease in the myofilament responsiveness to Ca2+. These effects on the membrane association of PKC and on contractility are enhanced by cell depolarization achieved by raising [KCl] in the bathing medium.

Which Arterial and Cardiac Parameters Best Predict Left Ventricular Mass

BACKGROUND Many cardiovascular and noncardiovascular parameters are thought to be determinants of left ventricular mass (LVM). Complicated interactions necessitate the simultaneous measurement and consideration of each to determine their individual and collective impact on LVM. We undertook such a comprehensive study. METHODS AND RESULTS The influence of anthropometry, cardiac size and contractility, arterial structure and function, as well as indices of lifestyle, physical activity, and dietary salt intake on LVM (by two-dimensionally guided M-mode echocardiography) was analyzed in 1315 Chinese subjects who were either normotensive or had untreated hypertension. Effects of many cardiac and arterial factors were assessed. In univariate analysis, almost all measured noncardiovascular, cardiac, and arterial variables were significantly correlated with LVM. In multivariate linear regression analyses, when age, sex, body habitus, fasting serum C-peptide level, dietary salt, physical activity, and lifestyle were accounted for, the optimum multivariate linear regression main effects model had an adjusted model r2 of 0.740, with 98% of the model variance accounted for by the 5 independent determinants of LVM: stroke volume (49.6%), systolic blood pressure (30.7%), contractility (14.7%), body mass index (1.8%), and aortic root diameter (1.6%). Other proposed arterial indices were significant independent determinants of LVM only when blood pressure was removed from the model and, even then, these indices not only resulted in less powerful prediction but also accounted for only a very small percentage of the total variance of LVM. CONCLUSIONS In a large population, we (1) confirmed that age, body habitus, and some indexes of arterial structure and function are independent determinants of LVM; (2) found aortic diameter to be an independent structural determinant of LVM; (3) demonstrated that the effects of the derived measures of arterial function were small and provided no better predictive power than blood pressure alone; and (4) showed that when the best measures of cardiac and vascular load were included, the single most potent predictor was an index of left ventricular size.