Konstantina Dipla

Myocyte Recovery After Mechanical Circulatory Support in Humans With End-Stage Heart Failure

BACKGROUND The failing myocardium is characterized by decreased force production, slowed relaxation, and depressed responses to beta-adrenergic stimulation. In some heart failure patients, heart function is so poor that a left ventricular assist device (LVAD) is inserted as a bridge to transplantation. In the present research, we investigated whether circulatory support with an LVAD influenced the functional properties of myocytes from the failing heart. METHODS AND RESULTS Myocytes were isolated from human explanted failing hearts (HF-myocytes) and failing hearts with antecedent LVAD support (HF-LVAD-myocytes). Studies of myocyte function indicated that the magnitude of contraction was greater (9.6+/-0.7% versus 6.9+/-0.5% shortening), the time to peak contraction was significantly abbreviated (0.37+/-0.01 versus 0.75+/-0.04 seconds), and the time to 50% relaxation was reduced (0.55+/-0.02 versus 1.45+/-0.11 seconds) in the HF-LVAD-myocytes compared with the HF-myocytes (P<0.05). The HF-LVAD-myocytes had larger contractions than the HF-myocytes at all frequencies of stimulation tested. The negative force-frequency relationship of the HF-myocytes was improved in HF-LVAD-myocytes but was not reversed. Responses to beta-adrenergic stimulation (by isoproterenol) were greater in HF-LVAD-myocytes versus HF-myocytes. CONCLUSIONS The results of the study strongly support the idea that circulatory support with an LVAD improves myocyte contractile properties and increases beta-adrenergic responsiveness.

The Sarcoplasmic Reticulum and the Na+/Ca2+ Exchanger Both Contribute to the Ca2+ Transient of Failing Human Ventricular Myocytes

Our objective was to determine the respective roles of the sarcoplasmic reticulum (SR) and the Na+/Ca2+ exchanger in the small, slowly decaying Ca2+ transients of failing human ventricular myocytes. Left ventricular myocytes were isolated from explanted hearts of patients with severe heart failure (n=18). Cytosolic Ca2+, contraction, and action potentials were measured by using indo-1, edge detection, and patch pipettes, respectively. Selective inhibitors of SR Ca2+ transport (thapsigargin) and reverse-mode Na+/Ca2+ exchange activity (No. 7943, Kanebo Ltd) were used to define the respective contribution of these processes to the Ca2+ transient. Ca2+ transients and contractions induced by action potentials (AP transients) at 0.5 Hz exhibited phasic and tonic components. The duration of the tonic component was determined by the action potential duration. Ca2+ transients induced by caffeine (Caf transients) exhibited only a phasic component with a rapid rate of decay that was dependent on extracellular Na+. The SR Ca2+-ATPase inhibitor thapsigargin abolished the phasic component of the AP Ca2+ transient and of the Caf transient but had no significant effect on the tonic component of the AP transient. The Na+/Ca2+ exchange inhibitor No. 7943 eliminated the tonic component of the AP transient and reduced the magnitude of the phasic component. In failing human myocytes, Ca2+ transients and contractions exhibit an SR-related, phasic component and a slow, reverse-mode Na+/Ca2+ exchange-related tonic component. These findings suggest that Ca2+ influx via reverse-mode Na+/Ca2+ exchange during the action potential may contribute to the slow decay of the Ca2+ transient in failing human myocytes.

The effects of a twenty-four-week aquatic training program on muscular strength performance in healthy elderly women.

The purpose of the present study was to determine the effectiveness of a 24-week aquatic training (AT) program, which included both aerobic and resistance components, on muscle strength (isometric and dynamic), flexibility, and functional mobility in healthy women over 60 years of age. Twenty-two subjects were assigned randomly to either an AT (n = 12) or a control (C, n = 10) group. Volunteers participated in a supervised shallow-water exercise program for 60 minutes a day, 3 days a week; the exercise program consisted of a 10-minute warm-up and stretching, 25 minutes of endurance-type exercise (dancing) at 80% of heart rate (HR)max, 20 minutes of upper- and lower-body resistance exercises with specialized water-resistance equipment, and a 5-minute cool down. Maximal isometric torque of knee extensors (KEXT) and knee flexors (KFLEX) were evaluated by a Cybex Norm dynamometer, grip strength (HGR) was evaluated using a Jamar hydraulic dynamometer, and dynamic strength was evaluated via the 3 repetition maximum (3RM) test for chest press, knee extension, lat pull down, and leg press. Jumping performance was evaluated using the squat jump (SJ), functional mobility with the timed up-and-go (TUG) test, and trunk flexion with the sit-and-reach test. Body composition was measured using the bioelectrical impedance method. The AT induced significant improvements in KEXT (10.5%) and KFLEX (13.4%) peak torque, HGR strength (13%), 3RM (25.7–29.4%), SJ (24.6%), sit-and-reach (11.6%), and TUG (19.8%) performance. The AT group demonstrated a significant increase in lean body mass (3.4%). No significant changes in these variables were observed in the C group. The results indicate that AT, with both aerobic and resistance components, is an alternative training method for improving neuromuscular and functional fitness performance in healthy elderly women.

Gender differences in post-infarction hypertrophy in end-stage failing hearts.

OBJECTIVES We explored whether there are gender differences in cardiac remodeling and whether etiology influences organ and cellular remodeling in advanced heart failure (HF). BACKGROUND Several studies have shown a survival benefit for women compared to men with symptomatic HF. This observation may be related to gender differences in cardiac remodeling. METHODS We studied hearts from 100 patients (72 men and 28 women) receiving cardiac transplantation at our institution. Cardiac morphology was assessed with echocardiography and direct measurement of cardiac mass. Cardiac myocyte volume, length, width, cross-sectional area, and contraction were measured using previously validated techniques. RESULTS Among 50 patients with idiopathic cardiomyopathy (CM), we observed no gender-based differences in cardiac or cellular remodeling. In contrast, among 50 patients with ischemic cardiomyopathy (ICM), the heart weight index was significantly greater in men, and there was a strong trend toward an increased left ventricular (LV) mass index as well. These gender differences in cardiac and LV mass were paralleled by marked gender differences in myocyte volume, such that average myocyte volume was 36% greater in men than in women, in association with a 14% increase in resting cell length. CONCLUSIONS Our studies demonstrate a multilevel gender difference in post-infarction remodeling, with women exhibiting reduced hypertrophy. Our studies further demonstrate that gender differences in cardiac remodeling in ICM are largely related to fundamental differences in cellular remodeling rather than simply differences in infarct size or expansion. Distinctions observed between ischemic and idiopathic CM suggest that gender may influence local myocardial responses to injury.

Recovery during high-intensity intermittent anaerobic exercise in boys, teens, and men

PURPOSE This study examined the effects of age on recovery of peak torque of knee extensors (PTEX) and flexors (PTFL), and total work (TW) during high-intensity intermittent 30-s (HI30) and 60-s (HI60) exercise in boys (N=19; age, 11.4+/-0.5 yr), teens (N=17; age, 14.7+/-0.4 yr), and men (N=18; age, 24.1+/-2.0 yr). METHODS Each age groups subjects were subdivided to participate in an HI30 or an HI60 protocol. The HI30 involved 4x18 maximal knee extensions and flexions (1-min rest between sets), and the HI60 comprised of 2x34 reps (2-min rest). PTEX (N.m.kg), PTFL (N.m.kg), and TW (J.kg) were recorded at each set. The percent recovery of PTEX, PTFL, and TW was calculated as percent of the value achieved in the first set. RESULTS In HI60, the percent recovery for PTEX, PTFL, and TW after the first set was higher in boys compared with teens and men (P<0.01). In HI30, the percent recovery for PTEX, PTFL, and TW was higher in boys compared with men in all sets (P<0.01), and in teens compared with men in the last two sets (P<0.05). The percent recovery of PTFL and TW was higher in boys compared with teens in the last two sets (P<0.05). Lactate increase was most pronounced in men, less pronounced in teens, and least pronounced in boys (P<0.01). Heart rate recovered faster in boys compared with teens and men in both protocols (P<0.05). CONCLUSIONS The recovery was faster in boys than in teens and men during HI30 and HI60, as evident by the greater percent recovery in boys for a given time. Furthermore, it appears that the rate of recovery during HI30 and HI60 anaerobic exercise is maturity dependent.

Sodium/calcium exchange contributes to contraction and relaxation in failed human ventricular myocytes

Defects in myocyte contraction and relaxation are key features of human heart failure. Sodium/calcium exchanger-mediated contribution to contraction and relaxation were separated from other mechanisms [L-type calcium current, sarco(endo)plasmic reticulum (SR) Ca(2+)-ATPase] based on voltage, temperature, and selective blockers. Rod-shaped left ventricular myocytes were isolated from failed human explants (n = 29) via perfusion with collagenase-containing Krebs solution. Action potentials using perforated patch and contractions using an edge detector were recorded at 0.5-1.5 Hz in Tyrode solution at 25 degrees C and 37 degrees C. Contraction duration was dependent on action potential (AP) duration at 37 degrees C but not at 25 degrees C, suggesting the role of the exchanger in relaxation and linking myocyte relaxation to the repolarization phase of the AP. Voltage-clamp experiments from -50 to +10 mV for 1,500 ms in Tyrode or Na(+)- and K(+)-free solutions after conditioning pulses triggered biphasic contractions that included a rapid SR-mediated component and a slower voltage-dependent exchanger-mediated component. We used thapsigargin to block the SR, which eliminated the rapid component, and we used an exchanger blocker, Kanebo 7943, which eliminated the slow component. The exchanger was shown to contribute to contraction through reverse-mode exchange, as well as to play a key role in relaxation of human ventricular myocytes.

Voltage-dependent Ca2+ release from the SR of feline ventricular myocytes is explained by Ca2+-induced Ca2+ release

1 Direct voltage‐gated (voltage‐dependent Ca2+ release, VDCR) and Ca2+ influx‐gated (Ca2+‐induced Ca2+ release, CICR) sarcoplasmic reticulum (SR) Ca2+ release were studied in feline ventricular myocytes. The voltage‐contraction relationship predicted by the VDCR hypothesis is sigmoidal with large contractions at potentials near the Ca2+ equilibrium potential (ECa). The relationship predicted by the CICR hypothesis is bell‐shaped with no contraction at ECa. 2 The voltage dependence of contraction was measured in ventricular myocytes at physiological temperature (37 °C), resting membrane potential and physiological [K+]. Experiments were performed with cyclic adenosine 3′,5′‐monophosphate (cAMP) in the pipette or in the presence of the β‐adrenergic agonist isoproterenol (isoprenaline; ISO). 3 The voltage‐contraction relationship was bell‐shaped in Na+‐free solutions (to eliminate the Na+ current and Na+‐Ca2+ exchange, NCX) but the relationship was broader than the L‐type Ca2+ current (ICa,L)‐voltage relationship. 4 Contractions induced with voltage steps from normal resting potentials to ‐40 mV are thought to represent VDCR rather than CICR. We found that cAMP and ISO shifted the voltage dependence of ICa,L activation to more negative potentials so that ICa,L was always present with steps to ‐40 mV. ICa,L at ‐40 mV inactivated when the holding potential was decreased (V½=−57·8 ± 0·49 mV). 5 ISO increased inward current, SR Ca2+ load and contraction in physiological [Na+] and a broad bell‐shaped voltage‐contraction relationship was observed. Inhibition of reverse‐mode NCX, decreasing ICa,L and decreasing SR Ca2+ loading all decreased contractions at strongly positive potentials near ECa. 6 The voltage‐contraction relationship in 200 μM cadmium (Cd2+) was bell‐shaped, supporting a role of ICa,L rather than VDCR. 7 All results could be accounted for by the CICR hypothesis, and many results exclude the VDCR hypothesis.

Reductive stress after exercise: The issue of redox individuality.

Exercise has been consistently used as an oxidant stimulus in redox biology studies. However, previous studies have focused on group differences and did not examine individual differences. As a result, it remains untested whether all individuals experience oxidative stress after acute exercise. Therefore, the main aim of the present study was to investigate whether some individuals exhibit unexpected responses after an acute eccentric (i.e., muscle-damaging) exercise session. Ninety eight (N = 98) young men performed an isokinetic eccentric exercise bout with the knee extensors. Plasma, erythrocytes and urine samples were collected immediately before and 2 days post-exercise. Three commonly used redox biomarkers (F2-isoprostanes, protein carbonyls and glutathione) were assayed. As expected, the two oxidant biomarkers (F2-isoprostanes and protein carbonyls) significantly increased 2 days after exercise (46% and 61%, respectively); whereas a significant decrease in glutathione levels (by −21%) was observed after exercise. A considerable number of the participants exhibited changes in the levels of biomarkers in the opposite, unexpected direction than the group average. More specifically, 13% of the participants exhibited a decrease in F2-isoprostanes and protein carbonyls and 10% of the participants exhibited an increase in glutathione levels. Furthermore, more than 1 out of 3 individuals exhibited either unexpected or negligible (from 0% to ± 5%) responses to exercise in at least one redox biomarker. It was also observed that the initial values of redox biomarkers are important predictors of the responses to exercise. In conclusion, although exercise induces oxidative stress in the majority of individuals, it can induce reductive stress or negligible stress in a considerable number of people. The data presented herein emphasize that the mean response to a redox stimulus can be very misleading. We believe that the wide variability (including the cases of reductive stress) described is not limited to the oxidant stimulus used and the biomarkers selected.

Effects of low- and high-volume resistance exercise on postprandial lipaemia

Postprandial lipaemia (PL) is associated with the metabolic syndrome, CVD and endothelial dysfunction. Aerobic exercise has been shown to reduce PL. Although resistance exercise is recommended for the improvement of the quality of life, management of body weight and prevention of several disorders, its effect on PL has received little attention. The present study examined the effects of low-volume resistance exercise (LVRE) and high-volume resistance exercise (HVRE) on PL. Ten healthy young men performed three trials, each conducted over 2 d. On the afternoon of day 1, they either refrained from exercise (control), performed LVRE (two sets of eight exercises, twelve repetitions at twelve repetitions maximum (RM) in each set; energy expenditure 0 x 76 MJ), or performed HVRE (four sets of eight exercises, twelve repetitions at 12 RM in each set; energy expenditure 1 x 40 MJ). On the morning of day 2 they consumed a meal containing 67 kJ/kg body weight, of which 65 % energy was from fat. Blood samples were obtained in the fasted state and for 6 h postprandially. The total area under the TAG curve (AUC; mmol/l x h) was lower (P<0 x 05) in HVRE (8 x 76 (sd 3 x 20)) and LVRE (9 x 29 (sd 3 x 64)) compared with control (11 x 60 (sd 4 x 35)). The incremental AUC was lower in HVRE compared with control (3 x 07 (sd 2 x 53) v. 5 x 58 (sd 3 x 72)), but not different between LVRE (3 x 86 (sd 2 x 29)) and control. In conclusion, resistance exercise of 1 x 40 MJ (four sets - eight exercises - twelve RM) or 0 x 76 MJ (two sets - eight exercises - twelve RM) before a high-fat meal reduces the total postprandial lipaemic response.

Effect of a hippotherapy intervention program on static balance and strength in adolescents with intellectual disabilities

The aim of this study was to assess the effects of a hippotherapy program on static balance and strength in adolescents with intellectual disability (ID). Nineteen adolescents with moderate ID were assigned either an experimental group (n=10) or a control group (n=9). The experimental group attended a 10-week hippotherapy program. To assess static balance, three tasks of increasing difficulty (Double-Leg Stance with opened or closed eyes, and One-Leg Stance with opened eyes) were performed while standing on an EPS pressure platform (Loran Engineering S.r.I., Bologna, Italy). The strength measurements consisted of three maximal isometric half-squats from the seating position (knee joint at 90°). The hippotherapy intervention program resulted in significant improvements in strength parameters, and on the more complex balance task (i.e. standing on one leg). In conclusion, this study provides evidence that hippotherapy can be used as an effective intervention for improving balance and strength in individuals with ID, and could thus influence functional activities and quality of life.