Oxidative stress, chronic inflammation, and telomere length in patients with periodontitis

The aim of this study was to determine leukocyte telomere length (LTL) in individuals with periodontitis and controls, exploring its relationship with systemic inflammation and oxidative stress. Five hundred sixty-three participants were recruited for this case-control study: 356 subjects with and 207 subjects without periodontitis. LTL was measured by a qPCR technique from leukocytes' DNA. Global measures of oxidative stress (reactive oxygen metabolites) and biological antioxidant potential in plasma were performed together with high-sensitivity assays for C-reactive protein (CRP). Leukocyte counts and lipid profiles were performed using standard biochemistry. Cases had higher levels of CRP (2.1±3.7mg/L vs 1.3±5.4mg/L, P<0.001) and reactive oxygen metabolites (378.1±121.1 U Carr vs 277.4±108.6 U Carr, P<0.001) compared to controls. Overall, cases had shorter LTL with respect to controls (1.23±0.42 vs 1.12±0.31T/S ratio, P=0.006), independent of age, gender, ethnicity, and smoking habit. When divided by subgroup of periodontal diagnosis (chronic, n=285; aggressive, n=71), only chronic cases displayed shorter LTL (P=0.01). LTL was negatively correlated with age (P=0.001; R=-0.2), oxidative stress (P=0.008; R=-0.2), and severity of periodontitis (P=0.003; R=-0.2) in both the whole population and the subgroups (cases and controls). We conclude that shorter telomere lengths are associated with a diagnosis of periodontitis and their measures correlate with the oxidative stress and severity of disease.     

Loss of responsiveness of circular smooth muscle cells from the guinea pig ileum is associated with changes in gap junction coupling

Gap junction coupling and neuromuscular transmission to smooth muscle were studied in the first 4 h after preparations were set up in vitro. Intracellular recordings were made from smooth muscle cells of guinea pig ileum. Fast inhibitory junction potentials (IJPs) were small (1.3 ± 1.0 mV) in the first 30 min but increased significantly over the first 120 min to 15.8 ± 0.9 mV (n = 12, P < 0.001). Comparable increases in slow IJPs and excitatory junction potentials were also observed. During the same period, resting membrane potential depolarized from -58.8 ± 1.4 to -47.2 ± 0.4 mV (n = 12, P < 0.001). Input resistance, estimated by intracellular current injection, decreased in parallel (P < 0.05), and dye coupling, measured by intracellular injection of carboxyfluorescein, increased (P < 0.001). Input resistance was higher and dye coupling was less in longitudinal than circular smooth muscle cells. Gap junction blockers [carbenoxolone (100 μM), 18β-glycyrrhetinic acid (10 μM), and 2-aminoethoxydiphenyl borate (50 μM)] hyperpolarized coupled circular smooth muscle cells, reduced the amplitude of fast and slow IJPs and excitatory junction potentials, increased input resistance, and reduced dye coupling. Local application of ATP (10 mM) mimicked IJPs and showed comparable increases in amplitude over the first 120 min; carbenoxolone and 2-aminoethoxydiphenyl borate significantly reduced ATP-evoked hyperpolarizations in coupled cells. In contrast, synaptic transmission between myenteric neurons was not suppressed during the first 30 min. Gap junction coupling between circular smooth muscle cells in isolated preparations was initially disrupted but recovered over the next 120 min to a steady level. This was associated with potent effects on neuromuscular transmission and responses to exogenous ATP.     

A method for detecting the temporal sequence of muscle activation during cycling using MRI

Surface electromyography (EMG) can assess muscle recruitment patterns during cycling, but has limited applicability to studies of deep muscle recruitment and electrically stimulated contractions. We determined whether muscle recruitment timing could be inferred from MRI-measured transverse relaxation time constant (T(2)) changes and a cycle ergometer modified to vary power as a function of pedal angle. Six subjects performed 6 min of single-leg cycling under two conditions (E0°-230° and E90°-230°), which increased the power from 0°-230° and 90-230° of the pedal cycle, respectively. The difference condition produced a virtual power output from 0-180° (V0°-180°). Recruitment was assessed by integrating EMG over the pedal cycle (IEMG) and as the (post-pre) exercise T(2) change (ΔT(2)). For E0°-230°, the mean IEMG for vastus medialis and lateralis (VM/VL; 49.3 ± 3.9 mV·s; mean ± SE) was greater (P < 0.05) than that for E90°-230° (17.9 ± 1.9 mV·s); the corresponding ΔT(2) values were 8.7 ± 1.0 and 1.4 ± 0.5 ms (P < 0.05). For E0°-230° and E90°-230°, the IEMG values for biceps femoris/long head (BF(L)) were 37.7 ± 5.4 and 27.1 ± 5.6 mV·s (P > 0.05); the corresponding ΔT(2) values were 0.9 ± 0.9 and 1.5 ± 0.9 ms (P > 0.05). MRI data indicated activation of the semitendinosus and BF/short head for E0°-230° and E90°-230°. For V0°-180°, ΔT(2) was 7.2 ± 0.9 ms for VM/VL and -0.6 ± 0.6 ms for BF(L); IEMG was 31.5 ± 3.7 mV·s for VM/VL and 10.6 ± 7.0 mV·s for BF(L). MRI and EMG data indicate VM/VL activity from 0 to 180° and selected hamstring activity from 90 to 230°. Combining ΔT(2) measurements with variable loading allows the spatial and temporal patterns of recruitment during cycling to be inferred from MRI data.     

产后抑郁症患者听感觉门控P50的研究

目的：探讨产后抑郁症患者感觉门控P50 的变化特征,为产后抑郁患者的早期预防提供参考依据。方法：采用配对听觉条件（S1）、测试（S2）刺激范式,对本院2011 年1 月至2012 年6 月收治的26 例产后抑郁症患者（实验组）进行听觉诱发电位P50检测,测量P50 的潜伏期、波幅,并与25 例健康被试者（对照组）的结果进行比较。结果：（1） 与对照组相比,实验组S1-P50 潜伏期[（56.62± 17.42） ms vs. （49.86 ± 15.21） ms],S2-P50 潜伏期[（57.36 ± 15.42） ms vs. （50.04 ± 16.27） ms]的差异均无统计学意义（P〉0.05）;（2）与对照组相比,实验组S1-P50 波幅[（3.58 ± 1.72） μV vs. （1.13 ± 0.91） μV]显著降低,差异有统计学意义（P〈0.05）;S2-P50 波幅[（1.32 ± 1.16） μV vs. （1.48 ± 1.05） μV]差异无统计学意义（P〉0.05）;（3） 与对照组相比,实验组S2/S1 波幅比值[（1.17 ± 0.26） vs.（0.41 ± 0.13）]显著升高,差异有统计学意义（P〈0.05）。结论：产后抑郁症患者感觉门控抑制能力有缺陷,P50 受损指标可能为评估产后抑郁症患者的潜在生物学指标。     

Modulated dispersion of activation and repolarization by premature beats in patients with cardiomyopathy at risk of sudden death

Premature beats can trigger ventricular arrhythmias in heart disease, but the mechanisms are not well defined. We studied the effect of premature beats on activation and repolarization dispersion in seven patients with cardiomyopathy (57 ± 10 yr, left ventricular ejection fraction 31 ± 7%). Activation time (AT), activation-recovery interval (ARI), and total repolarization time (TRT) were measured from 26 unipolar electrograms during right ventricle (RV) endocardial (early) to left ventricle epicardial (late) activation in response to RV apical extrastimulation (S1S2). Early TRT dispersion increased significantly with shorter S1S2 (1.0 ± 0.2 to 2.3 ± 0.4 ms/mm, P < 0.0001), with minimal change in late TRT dispersion (0.8 ± 0.1 to 1.0 ± 0.3 ms, P = 0.02). This was associated with an increase in early AT dispersion (1.0 ± 0.1 to 1.5 ± 0.2 ms/mm, P = 0.05) but no change in late AT dispersion (0.6 ± 0.1 to 0.7 ± 0.2 ms/mm, P = 0.4). Early and late ARI dispersion did not change with shorter S1S2. AT restitution slopes were similar between early and late sites, as was slope heterogeneity. ARI restitution slope was greater in early vs. late sites (1.3 ± 0.6 vs. 0.8 ± 0.6, P = 0.03), but slope heterogeneity was similar. With shorter S1S2, AT-ARI slopes became less negative (flattened) at both early (-0.4 ± 0.1 to +0.04 ± 0.2) and late (-1.5 ± 0.2 to +0.3 ± 0.2) sites, implying less activation-repolarization coupling. There was no difference in AT-ARI slopes between early and late sites at short S1S2. In conclusion, high-risk patients with cardiomyopathy have greater TRT dispersion at tightly coupled S1S2 due to greater AT dispersion and activation-repolarization uncoupling. Modulated dispersion is more pronounced at early vs. late activated sites, which may predispose to reentrant ventricular arrhythmias.     

Risk factors for immersion pulmonary edema: hyperoxia does not attenuate pulmonary hypertension associated with cold water-immersed prone exercise at 4.7 ATA

Hyperoxia has been shown to attenuate the increase in pulmonary artery (PA) pressure associated with immersed exercise in thermoneutral water, which could serve as a possible preventive strategy for the development of immersion pulmonary edema (IPE). We tested the hypothesis that the same is true during exercise in cold water. Six healthy volunteers instrumented with arterial and PA catheters were studied during two 16-min exercise trials during prone immersion in cold water (19.9-20.9°C) in normoxia [0.21 atmospheres absolute (ATA)] and hyperoxia (1.75 ATA) at 4.7 ATA. Heart rate (HR), Fick cardiac output (CO), mean arterial pressure (MAP), pulmonary artery pressure (PAP), pulmonary artery wedge pressure (PAWP), central venous pressure (CVP), arterial and venous blood gases, and ventilatory parameters were measured both early (E, 5-6 min) and late (L, 15-16 min) in exercise. During exercise at an average oxygen consumption rate (Vo(2)) of 2.38 l/min, [corrected] CO, CVP, and pulmonary vascular resistance were not affected by inspired (Vo(2)) [corrected] or exercise duration. Minute ventilation (Ve), alveolar ventilation (Va), and ventilation frequency (f) were significantly lower in hyperoxia compared with normoxia (mean ± SD: Ve 58.8 ± 8.0 vs. 65.1 ± 9.2, P = 0.003; Va 40.2 ± 5.4 vs. 44.2 ± 9.0, P = 0.01; f 25.4 ± 5.4 vs. 27.2 ± 4.2, P = 0.04). Mixed venous pH was lower in hyperoxia compared with normoxia (7.17 ± 0.07 vs. 7.20 ± 0.07), and this result was significant early in exercise (P = 0.002). There was no difference in mean PAP (MPAP: 28.28 ± 8.1 and 29.09 ± 14.3 mmHg) or PAWP (18.0 ± 7.6 and 18.7 ± 8.7 mmHg) between normoxia and hyperoxia, respectively. PAWP decreased from early to late exercise in hyperoxia (P = 0.002). These results suggest that the increase in pulmonary vascular pressures associated with cold water immersion is not attenuated with hyperoxia.     

Effect of exercise conditioning on excitation-contraction coupling in aged rats

We studied aged (24-26 mo) Fischer 344 rats after they underwent 8 wk of moderate exercise conditioning. Right ventricular papillary muscles were loaded with the calcium indicator aequorin. Electrophysiological recordings were also performed. Time to peak isometric tension in muscles from exercised aged rats (EAR) was shorter than in those from unexercised aged rats (UAR) (126 +/- 7 vs. 167 +/- 7 ms; P less than 0.01). Time to 50% relaxation from peak isometric tension was also shorter in EAR than in UAR (88 +/- 3 vs. 119 +/- 12 ms; P less than 0.05). There was a trend toward decrease in time to peak light and a significant decrease in time to 50% decline from peak light (33 +/- 4 ms in EAR vs. 59 +/- 17 ms in UAR; P = 0.001). Action potential amplitude was smaller in EAR than in UAR (67 +/- 4 vs. 82 +/- 3 mV; P = 0.003); however, action potential duration was longer (137 +/- 6 ms in EAR vs. 100 +/- 10 ms in UAR; P = 0.005). Right ventricular-to-body weight ratios revealed no evidence of hypertrophy in EAR compared with UAR. Cardiac tissue norepinephrine content was significantly greater in EAR than in UAR (1,212 +/- 25 vs. 630 +/- 105 ng/tissue; P = 0.02). In summary, exercise reversed the age-related prolongation of isometric contraction and associated intracellular calcium transient in the aged rat while it prolonged the transmembrane action potential. In addition, exercise in aged rats resulted in an increase in cardiac norepinephrine content.     

Diastolic dysfunction and intraventricular dyssynchrony are restored by low intensity exercise training in obese men

The aim of this study was to evaluate the impact of a low-intensity training program on subclinical cardiac dysfunction and on dyssynchrony in moderately obese middle aged men. Ten obese and 14 age-matched normal-weight men (BMI: 33.6 ± 1.0 and 24.2 ± 0.5 kg/m(2)) were included. Obese men participated in an 8-week low-intensity training program without concomitant diet. Cardiac function and myocardial synchrony were assessed by echocardiography with tissue Doppler imaging (TDI) and speckle tracking echocardiography (STE). At baseline, obese men showed diastolic dysfunction on standard echocardiography, lower strain values (systolic strain: 15.9 ± 0.9 vs. 18.8 ± 0.3%, diastolic strain rate: 0.81 ± 0.09 vs. 1.05 ± 0.06 s(-1)), and significant intraventricular dyssynchrony (systolic: 13.3 ± 2.1 vs. 5.4 ± 2.1 ms, diastolic: 17.4 ± 3.2 vs. 9.1 ± 2.1 ms) (P < 0.05 vs. controls for all variables). Training improved aerobic fitness, decreased systolic blood pressure and heart rate, and reduced fat mass without weight loss. Diastolic function, strain values (systolic strain: 17.4 ± 0.9%, diastolic strain rate: 0.96 ± 0.12 s(-1)) and intraventricular dyssynchrony (systolic: 3.3 ± 1.7 ms, diastolic: 5.5 ± 3.4 ms) improved significantly after training (P < 0.05 vs. baseline values for all variables), reaching levels similar to those of normal-weight men. In conclusion, in obese men, a short and easy-to-perform low intensity training program restored diastolic function and cardiac synchrony and improved body composition without weight loss.     

腺苷抗豚鼠室性心律失常的电生理研究

实验用全细胞膜片钳技术在单个豚鼠心室肌细胞上研究了腺苷 (Ado)对正常及异丙肾上腺素 (Iso)致豚鼠心室肌细胞动作电位、迟后除极 (DAD)、L 型钙电流 (ICa.L)和短暂内向电流 (Iti)的作用。结果表明 :(1)Ado在2 0～ 10 0 μmol/L时对豚鼠心室肌细胞动作电位和ICa .L无明显直接作用 ,但却可明显降低Iso所致的动作电位时程(APD)延长和ICa .L峰值增大 ,Iso (10nmol/L)使细胞APD50 从 3 40± 2 1ms延长到 486± 2 8ms (P <0 0 1) ,APD90从 3 61± 17ms延长至 5 0 1± 2 9ms (P <0 0 1) ;ICa .L峰值从 - 6 5 3± 1 4pA/pF增大到 - 18 2 8± 2 4pA/pF (P <0 0 1) ,电流电压曲线明显左移和下移 ;Ado (5 0 μmol/L)使APD50 和APD90 降至 40 3± 19ms和 419± 2 6ms ,但并不影响动作电位其它参数 ,使ICa.L峰值降低至 - 10 2± 1 5pA/pF (P <0 0 1)。 (2 )Iso (3 0nmol/L)可诱发心室肌细胞产生DADs,其发生率为 10 0 % ;Ado (5 0 μmol/L)可完全抑制Iso引发DADs;细胞经 - 40～ +2 0mV、时程 2s的除极电压 ,Iso (3 0nmol/L)诱导出Iti,其发生率为 10 0 % ;Ado (5 0 μmol/L)可明显抑制Iso致Iti的发生 ,其发生率降为 14 3 %。研究结果提示 ,Ado对豚鼠心室肌细胞动作电位和ICa.L无明显直接作用 ,但却可显著降低Is     

Whole-Body Water Flow Stimulation to the Lower Limbs Modulates Excitability of Primary Motor Cortical Regions Innervating the Hands: A Transcranial Magnetic Stimulation Study

Whole-body water immersion (WI) has been reported to change sensorimotor integration. However, primary motor cortical excitability is not affected by low-intensity afferent input. Here we explored the effects of whole-body WI and water flow stimulation (WF) on corticospinal excitability and intracortical circuits. Eight healthy subjects participated in this study. We measured the amplitude of motor-evoked potentials (MEPs) produced by single transcranial magnetic stimulation (TMS) pulses and examined conditioned MEP amplitudes by paired-pulse TMS. We evaluated short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) using the paired-TMS technique before and after 15-min intervention periods. Two interventions used were whole-body WI with water flow to the lower limbs (whole-body WF) and whole-body WI without water flow to the lower limbs (whole-body WI). The experimental sequence included a baseline TMS assessment (T0), intervention for 15 min, a second TMS assessment immediately after intervention (T1), a 10 min resting period, a third TMS assessment (T2), a 10 min resting period, a fourth TMS assessment (T3), a 10 min resting period, and the final TMS assessment (T4). SICI and ICF were evaluated using a conditioning stimulus of 90% active motor threshold and a test stimulus adjusted to produce MEPs of approximately 1–1.2 mV, and were tested at intrastimulus intervals of 3 and 10 ms, respectively. Whole-body WF significantly increased MEP amplitude by single-pulse TMS and led to a decrease in SICI in the contralateral motor cortex at T1, T2 and T3. Whole-body WF also induced increased corticospinal excitability and decreased SICI. In contrast, whole-body WI did not change corticospinal excitability or intracortical circuits.     

Tubuloglomerular feedback response in the prenatal and postnatal ovine kidney

The tubuloglomerular feedback mechanism (TGF) plays an important role in regulating single-nephron glomerular filtration rate (GFR) by coupling distal tubular flow to arteriolar tone. It is not known whether TGF is active in the developing kidney or whether it can regulate renal vascular tone and thus GFR during intrauterine life. TGF characteristics were examined in late-gestation ovine fetuses and lambs under normovolemic and volume-expanded (VE) conditions. Lambs and pregnant ewes were anesthetized and the fetuses were delivered via a caesarean incision into a heated water bath, with the umbilical cord intact. Under normovolemic conditions, mean arterial pressure of the fetuses was lower than lambs (51 ± 1 vs. 64 ± 3 mmHg). The maximum TGF response (ΔP(SFmax)) was found to be lower in fetuses than lambs when tubular perfusion was increased from 0 to 40 nl/min (5.4 ± 0.7 vs. 10.6 ± 0.4 mmHg). Furthermore, the flow rate eliciting half-maximal response [turning point (TP)] was 15.7 ± 0.9 nl/min in fetuses compared with 19.3 ± 1.0 nl/min in lambs, indicating a greater TGF sensitivity of the prenatal kidney. VE decreased ΔP(SFmax) (4.2 ± 0.4 mmHg) and increased TP to 23.7 ± 1.3 nl/min in lambs. In fetuses, VE increased stop-flow pressure from 26.6 ± 1.5 to 30.3 ± 0.8 mmHg, and reset TGF sensitivity so that TP increased to 21.3 ± 0.7 nl/min, but it had no effect on ΔP(SFmax). This study provides direct evidence that the TGF mechanism is active during fetal life and responds to physiological stimuli. Moreover, reductions in TGF sensitivity may contribute to the increase in GFR at birth.     

Sympathetic nerve activity and whole body heat stress in humans

We and others have shown that moderate passive whole body heating (i.e., increased internal temperature ～0.7°C) increases muscle (MSNA) and skin sympathetic nerve activity (SSNA). It is unknown, however, if MSNA and/or SSNA continue to increase with more severe passive whole body heating or whether these responses plateau following moderate heating. The aim of this investigation was to test the hypothesis that MSNA and SSNA continue to increase from a moderate to a more severe heat stress. Thirteen subjects, dressed in a water-perfused suit, underwent at least one passive heat stress that increased internal temperature ～1.3°C, while either MSNA (n = 8) or SSNA (n = 8) was continuously recorded. Heat stress significantly increased mean skin temperature (Δ～5°C, P < 0.001), internal temperature (Δ～1.3°C, P < 0.001), mean body temperature (Δ～2.0°C, P < 0.001), heart rate (Δ～40 beats/min, P < 0.001), and cutaneous vascular conductance [Δ～1.1 arbitrary units (AU)/mmHg, P < 0.001]. Mean arterial blood pressure was well maintained (P = 0.52). Relative to baseline, MSNA increased midway through heat stress (Δ core temperature 0.63 ± 0.01°C) when expressed as burst frequency (26 ± 14 to 45 ± 16 bursts/min, P = 0.001), burst incidence (39 ± 13 to 48 ± 14 bursts/100 cardiac cyles, P = 0.03), or total activity (317 ± 170 to 489 ± 150 units/min, P = 0.02) and continued to increase until the end of heat stress (burst frequency: 61 ± 15 bursts/min, P = 0.01; burst incidence: 56 ± 11 bursts/100 cardiac cyles, P = 0.04; total activity: 648 ± 158 units/min, P = 0.01) relative to the mid-heating stage. Similarly, SSNA (total activity) increased midway through the heat stress (normothermia; 1,486 ± 472 to mid heat stress 6,467 ± 5,256 units/min, P = 0.03) and continued to increase until the end of heat stress (11,217 ± 6,684 units/min, P = 0.002 vs. mid-heat stress). These results indicate that both MSNA and SSNA continue to increase as internal temperature is elevated above previously reported values.     

Left ventricular systolic torsion correlates global cardiac performance during dyssynchrony and cardiac resynchronization therapy

Left ventricular (LV) systolic torsion is a primary mechanism contributing to stroke volume (SV). We hypothesized that change in LV torsion parallels changes in global systolic performance during dyssynchrony and cardiac resynchronization therapy (CRT). Seven anesthetized open chest dogs had LV pressure-volume relationship. Apical, basal, and mid-LV cross-sectional echocardiographic images were studied by speckle tracking analysis. Right atrial (RA) pacing served as control. Right ventricular (RV) pacing simulated left bundle branch block. Simultaneous RV-LV free wall and RV-LV apex pacing (CRTfw and CRTa, respectively) modeled CRT. Dyssynchrony was defined as the time difference in peak strain between earliest and latest segments. Torsion was calculated as the maximum difference between the apical and basal rotation. RA pacing had minimal dyssynchrony (52 ± 36 ms). RV pacing induced dyssynchrony (189 ± 61 ms, P < 0.05). CRTa decreased dyssynchrony (46 ± 36 ms, P < 0.05 vs. RV pacing), whereas CRTfw did not (110 ± 96 ms). Torsion during baseline RA was 6.6 ± 3.7°. RV pacing decreased torsion (5.1 ± 3.6°, P < 0.05 vs. control), and reduced SV, stroke work (SW), and dP/dt(max) compared with RA (21 ± 5 vs. 17 ± 5 ml, 252 ± 61 vs. 151 ± 64 mJ, and 2,063 ± 456 vs. 1,603 ± 424 mmHg/s, respectively, P < 0.05). CRTa improved torsion, SV, SW, and dP/dt(max) compared with RV pacing (7.7 ± 4.7°, 23 ± 3 ml, 240 ± 50 mJ, and 1,947 ± 647 mmHg/s, respectively, P < 0.05), whereas CRTfw did not (5.1 ± 3.6°, 18 ± 5 ml, 175 ± 48 mJ, and 1,699 ± 432 mmHg/s, respectively, P < 0.05). LV torsion changes covaried across conditions with SW (y = 0.94x+12.27, r = 0.81, P < 0.0001) and SV (y = 0.66x+0.91, r = 0.81, P < 0.0001). LV dyssynchrony changes did not correlate with SW or SV (r = -0.12, P = 0.61 and r = 0.08, P = 0.73, respectively). Thus, we conclude that LV torsion is primarily altered by dyssynchrony, and CRT that restores LV performance also restores torsion.     

Calcium sparks in human ventricular cardiomyocytes from patients with terminal heart failure

Cardiomyocytes from terminally failing hearts display significant abnormalities in e-c-coupling, contractility and intracellular Ca(2+) handling. This study is the first to demonstrate the influence of end-stage heart failure on specific properties of Ca(2+) sparks in human ventricular cardiomyocytes. We investigated the frequency and characteristics of spontaneously arising Ca(2+) sparks in single isolated human myocytes from terminally failing (HF) and non-failing (NF) control myocardium by using the Ca(2+) indicator Fluo-3. The Ca(2+) sparks were recorded by line-scan images along the longitudinal axis of the myocytes at a frequency of 250Hz. After loading the sarcoplasmic reticulum (SR) with Ca(2+) by repetitive field stimulation (10 pulses at 1Hz) the frequency of the Ca(2+) sparks immediately after stimulation (t = 0s) was reduced significantly in HF compared to NF (4.15 +/- 0.42 for NF vs. 2.81 +/- 0.20 for HF sparks s(-1), P = 0.05). This difference was present constantly in line-scan recordings up to 15s duration (t = 15s: 2.75 +/- 0.65 for NF vs. 1.36 +/- 0.34 for HF sparks s(-1), P = 0.05). The relative amplitude (F/F(0)) of Ca(2+) sparks was also significantly lower in HF cardiomyocytes (1.33 +/- 0.015 NF vs. 1.19 +/- 0.003 HF, t = 0s) and during subsequent recordings of 15s. Significant differences between HF and NF were also present in calculations of specific spark properties. The time to peak was estimated at 25.75 +/-0.88ms in HF and 18.68 +/- 0.45ms in NF cardiomyocytes (P = 0.05). Half-time of decay was 66.48 +/- 1.89ms (HF) vs. 44.15 +/- 1.65ms (NF, P < 0.05), and the full width at half-maximum (FWHM) was 3.99 +/- 0.06 microm (HF) vs. 3.5 +/- 0.07 microm (NF, P < 0.05). These data support the hypothesis that even in the absence of cardiac disease, Ca(2+) sparks from human cardiomyocytes differ from previous results of animal studies with respect to the time-to-peak, half-time of decay and FWHM. The role of elevated external Ca(2+) in HF was studied by recording Ca(2+) sparks in HF cardiomyocytes with 10mmol external Ca(2+) concentration. Under these conditions, the average spark amplitude was increased from 1.19 +/- 0.003 (F/F(0), 2mmol Ca(2+)) to 1.26 +/- 0.01 (F/F(0), 10mmol Ca(2+)). We conclude that human heart failure causes distinct changes in Ca(2+) spark frequency and characteristics comparable to results established in animal models of heart failure. A reduced Ca(2+) load of the SR alone is unlikely to account for the observed differences between HF and NF and additional alterations in intracellular Ca(2+) release mechanisms must be postulated.     

Exercise training blunts oxidative stress in sickle cell trait carriers

The aim of this study was to analyze the effects of exercise training on oxidative stress in sickle cell trait carriers. Plasma levels of oxidative stress [advanced oxidation protein products (AOPP), protein carbonyl, malondialdehyde (MDA), and nitrotyrosine], antioxidant markers [catalase, glutathione peroxidase (GPX), and superoxide dismutase (SOD)], and nitrite and nitrate (NOx) were assessed at baseline, immediately following a maximal exercise test (T(ex)), and during recovery (T(1h), T(2h), T(24h)) in trained (T: 8 h/wk minimum) and untrained (U: no regular physical activity) sickle cell trait (SCT) carriers or control (CON) subjects (T-SCT, n = 10; U-SCT, n = 8; T-CON, n = 11; and U-CON, n = 11; age: 23.5 ± 2.2 yr). The trained subjects had higher SOD activities (7.6 ± 5.4 vs. 5.2 ± 2.1 U/ml, P = 0.016) and lower levels of AOPP (142 ± 102 vs. 177 ± 102 μM, P = 0.028) and protein carbonyl (82.1 ± 26.0 vs. 107.3 ± 30.6 nm/ml, P = 0.010) than the untrained subjects in response to exercise. In response to exercise, U-SCT had a higher level of AOPP (224 ± 130 vs. 174 ± 121 μM, P = 0.012), nitrotyrosine (127 ± 29.1 vs.70.6 ± 46.6 nM, P = 0.003), and protein carbonyl (114 ± 34.0 vs. 86.9 ± 26.8 nm/ml, P = 0.006) compared with T-SCT. T-SCT had a higher SOD activity (8.50 ± 7.2 vs. 4.30 ± 2.5 U/ml, P = 0.002) and NOx (28.8 ± 11.4 vs. 14.6 ± 7.0 μmol·l(-1)·min(-1), P = 0.003) in response to exercise than U-SCT. Our data indicate that the overall oxidative stress and nitric oxide response is improved in exercise-trained SCT carriers compared with their untrained counterparts. These results suggest that physical activity could be a viable method of controlling the oxidative stress. This could have a beneficial impact because of its involvement in endothelial dysfunction and subsequent vascular impairment in hemoglobin S carriers.     

Role of skeletal muscle mitochondrial density on exercise-stimulated lipid oxidation

Reduced skeletal muscle mitochondrial density is proposed to lead to impaired muscle lipid oxidation and increased lipid accumulation in sedentary individuals. We assessed exercise-stimulated lipid oxidation by imposing a prolonged moderate-intensity exercise in men with variable skeletal muscle mitochondrial density as measured by citrate synthase (CS) activity. After a 2-day isoenergetic high-fat diet, lipid oxidation was measured before and during exercise (650 kcal at 50% VO(2)max) in 20 healthy men with either high (HI-CS = 24 ± 1; mean ± s.e.) or low (LO-CS = 17 ± 1 nmol/min/mg protein) muscle CS activity. Vastus lateralis muscle biopsies were obtained before and immediately after exercise. Respiratory exchange data and blood samples were collected at rest and throughout the exercise. HI-CS subjects had higher VO(2)max (50 ± 1 vs. 44 ± 2 ml/kg fat free mass/min; P = 0.01), lower fasting respiratory quotient (RQ) (0.81 ± 0.01 vs. 0.85 ± 0.01; P = 0.04) and higher ex vivo muscle palmitate oxidation (866 ± 168 vs. 482 ± 78 nmol/h/mg muscle; P = 0.05) compared to LO-CS individuals. However, whole-body exercise-stimulated lipid oxidation (20 ± 2 g vs. 19 ± 1 g; P = 0.65) and plasma glucose, lactate, insulin, and catecholamine responses were similar between the two groups. In conclusion, in response to the same energy demand during a moderate prolonged exercise bout, reliance on lipid oxidation was similar in individuals with high and low skeletal muscle mitochondrial density. This data suggests that decreased muscle mitochondrial density may not necessarily impair reliance on lipid oxidation over the course of the day since it was normal under a high-lipid oxidative demand condition. Twenty-four-hour lipid oxidation and its relationship with mitochondrial density need to be assessed.     

Differential regulation of sympathetic burst frequency and amplitude following acute hypoxia in humans

Current evidence suggests that the persistent sympathetic nerve activity (SNA), commonly observed after exposure to hypoxia (HX), is mediated by chemoreceptor sensitization and or baroreflex resetting. Evidence in humans and animals suggests that these reflexes may independently regulate the frequency (gating) and amplitude (neuronal recruitment) of SNA bursts. In humans (n = 7), we examined the regulation of SNA following acute isocapnic HX (5 min; end-tidal Po(2) = 45 Torr) and euoxic hypercapnia (HC; 5 min; end-tidal Pco(2) = +10 from baseline). HX increased SNA burst frequency (21 ± 7 to 28 ± 8 bursts/min, P < 0.05) and amplitude (99 ± 10 to 125 ± 19 au, P < 0.05) as did HC (14 ± 6 to 22 ± 10 bursts/min, P < 0.05 and 100 ± 12 to 133 ± 29 au, P < 0.05, respectively). Burst frequency (26 ± 7 bursts/min, P < 0.05), but not amplitude (97 ± 12 au), remained elevated 10 min post-HX. The change in burst amplitude (but not frequency) was significantly related to the measured change in ventilation (r(2) = 0.527, P < 0.001). Both frequency and amplitude decreased during recovery following HC. These data indicate the differential regulation of pattern and magnitude of sympathetic outflow in humans with sympathetic persistence following HX being specific to burst frequency and not amplitude.     

Effects of reduced PO2 on rapid-drive-induced hyperpolarization of diastolic transmembrane potential in feline cardiac Purkinje strands

Using standard microelectrode techniques, we evaluated effects of diminished oxygen tension on the magnitude and time course of frequency dependent changes in maximum diastolic transmembrane potential (MDP) and on alteration of action potential duration (APD) in feline Purkinje fibers. MDP was recorded continuously during a control period (cycle length (CL) = 1000 ms), during a 5-min period of rapid drive (CL = 400 ms) and following return to pacing CL = 1000 ms. Rapid drive resulted in hyperpolarization of MDP from control value; and after return to pacing CL = 1000 ms. MDP gradually depolarized, eventually attaining a steady state value within +/- 0.5 mV of the control value. The difference between hyperpolarized MDP value and final steady-state value was designated VH, and the decline of MDP towards steady-state value approximated an exponential function (time constant = tau VH). Exposure to reduced PO2 (75 +/- 2.1 mmHg vs. control 473 +/- 39.1 mmHg) (1 mmHg = 133.322 Pa) resulted in reduction in the magnitude of VH (6.2 +/- 3.43 mV vs. 7.8 +/- 2.73 mV, mean +/- SD, p less than 0.005) and shortening of APD within 0-24 min, while measurable prolongation of tau VH (75 +/- 18.5 vs. 54 +/- 9.0 s, p less than 0.005) began at 25-49 min following onset of reduced PO2. These observations suggest that rate-related changes of MDP in cardiac tissues are oxygen dependent, and they support previously reported analagous observations in nerve which suggested that frequency dependent potential changes may in part reflect alterations of electrogenic Na-K pump activity.     

Short-term exercise reduces markers of hepatocyte apoptosis in nonalcoholic fatty liver disease

Increased hepatocyte apoptosis is a hallmark of nonalcoholic fatty liver disease (NAFLD) and contributes to the profibrogenic state responsible for the progression to nonalcoholic steatohepatitis (NASH). Strategies aimed at reducing apoptosis may result in better outcomes for individuals with NAFLD. We therefore examined the effect of a short-term exercise program on markers of apoptosis-plasma cytokeratin 18 (CK18) fragments, alanine aminotransferase (ALT), aspartate aminotransferase (AST), soluble Fas (sFas), and sFas ligand (sFasL)-in 13 obese individuals with NAFLD [body mass index 35.2 ± 1.2 kg/m(2), >5% intrahepatic lipid (IHL) assessed by (1)H-MR spectroscopy]. Exercise consisted of treadmill walking for 60 min/day on 7 consecutive days at ～85% of maximal heart rate. Additionally, subjects underwent an oral glucose tolerance test and a maximal oxygen consumption (Vo(2max)) test before and after the exercise intervention. The Matsuda index was used to assess insulin sensitivity. We observed significant decreases in CK18 fragments (558.4 ± 106.8 vs. 323.4 ± 72.5 U/l, P < 0.01) and ALT (30.2 ± 5.1 vs. 24.3 ± 4.8 U/l, P < 0.05), and an increase in whole body fat oxidation (49.3 ± 6.1 vs. 69.4 ± 7.1 mg/min, P < 0.05), while decreases in circulating sFasL approached statistical significance (66.5 ± 6.0 vs. 63.0 ± 5.7 pg/ml, P = 0.06), as did the relationship between percent change in circulating CK18 fragments and ALT (r = 0.55, P = 0.05). We also observed a significant correlation between changes in fat oxidation and circulating sFasL (rho = -0.65, P < 0.05). There was no change in IHL following the intervention (18.2 ± 2.5 vs. 17.5 ± 2.1%, NS). We conclude that short-term exercise reduces a circulatory marker of hepatocyte apoptosis in obese individuals with NAFLD and propose that changes in the proapoptotic environment may be mediated through improved insulin sensitivity and increased oxidative capacity.