Recovery Time Constant Research Articles

Effects of exercise‐induced intracellular acidosis on the phosphocreatine recovery kinetics: a 31P MRS study in three muscle groups in humans

Little is known about the metabolic differences that exist among different muscle groups within the same subjects. Therefore, we used (31)P-magnetic resonance spectroscopy ((31)P-MRS) to investigate muscle oxidative capacity and the potential effects of pH on PCr recovery kinetics between muscles of different phenotypes (quadriceps (Q), finger (FF) and plantar flexors (PF)) in the same cohort of 16 untrained adults. The estimated muscle oxidative capacity was lower in Q (29 ± 12 mM min(-1), CV(inter-subject) = 42%) as compared with PF (46 ± 20 mM min(-1), CV(inter-subject) = 44%) and tended to be higher in FF (43 ± 35 mM min(-1), CV(inter-subject) = 80%). The coefficient of variation (CV) of oxidative capacity between muscles within the group was 59 ± 24%. PCr recovery time constant was correlated with end-exercise pH in Q (p < 0.01), FF (p < 0.05) and PF (p < 0.05) as well as proton efflux rate in FF (p < 0.01), PF (p < 0.01) and Q (p = 0.12). We also observed a steeper slope of the relationship between end-exercise acidosis and PCr recovery kinetics in FF compared with either PF or Q muscles. Overall, this study supports the concept of skeletal muscle heterogeneity by revealing a comparable inter- and intra-individual variability in oxidative capacity across three skeletal muscles in untrained individuals. These findings also indicate that the sensitivity of mitochondrial respiration to the inhibition associated with cytosolic acidosis is greater in the finger flexor muscles compared with locomotor muscles, which might be related to differences in permeability in the mitochondrial membrane and, to some extent, to proton efflux rates.

Effects of the antianginal drug, ranolazine, on the brain sodium channel NaV1.2 and its modulation by extracellular protons

Ranolazine is an antianginal drug currently approved for treatment of angina pectoris in the United States. Recent studies have focused on its effects on neuronal channels and its possible therapeutic uses in the nervous system. We characterized how ranolazine affects the brain sodium channel, Na(V)1.2, and how its actions are modulated by low pH. In this way, we further explore ranolazine's potential as an anticonvulsant and its efficacy in conditions like those during an ischaemic stroke. We performed whole-cell patch-clamp experiments on the voltage-gated sodium channel, Na(V)1.2. Experiments were performed with extracellular solution titrated to either pH 7.4 or pH 6.0 before and after ranolazine perfusion. Ranolazine accelerates onset and slows recovery of fast and slow inactivation. Ranolazine increases the maximum probability of use-dependent inactivation and reduces macroscopic and ramp sodium currents at pH 7.4. pH 6.0 reduced the slowing of fast inactivation recovery and inhibited use-dependent block by ranolazine. In the presence of ranolazine, the time constants of slow inactivation recovery and onset were significantly increased at pH 6.0 relative to pH 7.4 with 100 μM ranolazine. Our work provides novel insights into the modulation of brain sodium channel, Na(V)1.2, by ranolazine. We demonstrate that ranolazine binds Na(V)1.2 in a state-dependent manner, and that the effects of ranolazine are slowed but not abolished by protons. Our results suggest that further research performed on channels with epilepsy-causing mutations may prove ranolazine to be an efficacious therapy.

Repetitive transcranial magnetic stimulation increases excitability of hippocampal CA1 pyramidal neurons

Repetitive transcranial magnetic stimulation (rTMS) is able to induce alteration in cortical activity and excitability that outlast the period of stimulation, which is long-term depre-ssion (LTD) or long-term potentiation (LTP)-like. Accumulating evidence shows that Na+, Ca2+ and K+ channels are important for the regulation of neuronal excitability. To investigate the possible mechanisms of rTMS on regulation of intrinsic excitability in hippocampal neurons, the male or female Sprague-Dawley rats aged 2–3d or 7–8d were treated with 14 or 7-d's low frequency (1Hz) rTMS (400stimuli/d), respectively. After that, the effects of rTMS on ion channels such as Na+-channel, A-type K+-channel and Ca2+-channel in rat hippocampal CA1 pyramidal neurons were performed by standard whole-cell patch-clamp technique. The results showed that the peak amplitude and maximal rise slope of evoked single action potential (AP) were significantly increased after 14-d's rTMS treatment. Meanwhile, the AP threshold was significantly more depolarized in neurons after 14-d's rTMS treatment than neurons in control group that without rTMS treatment. The spontaneous excitatory post-synaptic currents (sEPSCs) frequency and amplitude of CA1 pyramidal neurons in groups with rTMS treatment (both 7d and 14d) were obviously increased compared with the age-matched control group. Furthermore, we found that electrophysiological properties of Na+-channel were markedly changed after rTMS treatment, including negative-shifted activation and inactivation curves, as well as fasten recovery rate. After rTMS application, the IA amplitude of K+-channel was reduced; the activation and inactivation curves of K+-channel were significantly shifted to right. Time constant of recovery from inactivation was also more rapid. Moreover, rTMS induced an obvious increment in the maximal current peak amplitude of Ca2+-channel. At the same time, there was a significant rightward shift in the activation curve and inactivation curves of Ca2+-channel. These data suggest that rTMS can enhance the AP and sEPSCs of hippocampal CA1 neurons. Altered electrophysiological properties of Na+-channel, A-type K+ channels and Ca2+ channels contribute to the underling mechanisms of rTMS-induced up-regulation of neural excitability.

Short‐term training alters the control of mitochondrial respiration rate before maximal oxidative ATP synthesis

Short-term exercise training may induce metabolic and performance adaptations before any changes in mitochondrial enzyme potential. However, there has not been a study that has directly assessed changes in mitochondrial oxidative capacity or metabolic control as a consequence of such training in vivo. Therefore, we used (31) P-magnetic resonance spectroscopy ((31) P-MRS) to examine the effect of short-term plantar flexion exercise training on phosphocreatine (PCr) recovery kinetics and the control of respiration rate. To this aim, we investigated 12 healthy men, experienced with this exercise modality (TRA), and 7 time-control subjects (TC). After 5 days of training, maximum work rate during incremental plantar flexion exercise was significantly improved (P < 0.01). During the recovery period, the maximal rate of oxidative adenosine triphosphate synthesis (PRE: 28 ± 13 mm min(-1) ; POST: 26 ± 15 mm min(-1) ) and the PCr recovery time constant (PRE: 31 ± 19 s; POST: 29 ± 16) were not significantly altered. In contrast, the Hill coefficient (nH ) describing the co-operativity between respiration rate and ADP was significantly increased in TRA (PRE: nH = 2.7 ± 1.4; POST: nH = 3.4 ± 1.9, P < 0.05). Meanwhile, there were no systematic variations in any of these variables in TC. This study reveals that 5 days of training induces rapid adaptation in the allosteric control of respiration rate by ADP before any substantial improvement in muscle oxidative capacity occurs.

Refined NBTI characterization of arbitrarily stressed PMOS devices at ultra-low and unique temperatures

We reexamine degradation and recovery dynamics in the negative bias temperature instability (NBTI) of p-channel metal oxide semiconductor field effect transistors (PMOSFETs) by making use of the recently developed in situ polyheater technique. The capability of switching the device temperature extremely fast and almost arbitrarily allows for measuring differently stressed devices directly after the termination of stress at a unique and much lower characterization temperature (e.g. −60°C). This procedure (‘degradation quenching’) is a powerful extension of the conventional measure–stress–measure (MSM) technique and provides a cleaner way for comparing threshold voltage shifts and charge pumping (CP) currents of arbitrarily stressed devices. We find that increasing the stress bias predominantly activates a larger number of defects with similar (short) recovery time constants causing steeper threshold voltage recovery transients after the termination of stress. Increasing the stress temperature has a very similar effect on the threshold voltage shift as increasing the stress time. In both cases, defects with larger recovery time constants are activated while the number of defects with short recovery time constants remains essentially the same. A comparison of VTH shift and CP data suggests that the total threshold voltage shift is due to at least two fundamentally different types of defects, one being readily recoverable and uncorrelated to the CP current while the other is ‘quasi-permanent’ and proportional to the CP current. By converting CP currents into corresponding threshold voltage shifts, we find that only about 50% of the ‘quasi-permanent’ VTH damage is due to slowly-recoverable interface states. The remaining fraction is due to another, yet undefined, positively charged defect generated at virtually the same rate.

The effect of PI3 kinase inhibitor LY294002 on voltage-dependent K+ channels in rabbit coronary arterial smooth muscle cells

AimsWe examined the effect of LY294002, a phosphatidylinositol 3-kinase (PI3K) inhibitor, on voltage-dependent K+ (Kv) channels. Main methodsElectrophysiological recordings were performed in freshly isolated rabbit coronary arterial smooth muscle cells. Key findingsThe Kv current amplitude was inhibited by LY294002 in a dose-dependent manner, with a Kd value of 1.48μM. Without alteration of the kinetics of activation, LY294002 accelerated the decay rate of Kv channel inactivation. The rate constants of association and dissociation for LY294002 were 1.83±0.01μM−1s−1 and 2.59±0.14s−1, respectively. Application of LY294002 had no significant impact on the steady-state activation or inactivation curves. In the presence of LY294002, the recovery time constant from inactivation was increased, and Kv channel inhibition increased under train pulses (1 or 2Hz). This indicates that LY294002-induced Kv channel inhibition is use-dependent. Furthermore, pretreatment with another PI3K inhibitor, wortmannin (10μM), did not affect the Kv current, and did not change the inhibitory effect of LY294002. SignificanceBased on these results, we suggest that LY294002 directly blocks Kv current irrespective of PI3K inhibition.

Short‐term training alters the control of mitochondrial respiration rate before maximal oxidative ATP synthesis

BackgroundThere has not been a study that has directly assessed temporal changes in mitochondrial oxidative capacity and metabolic control as a consequence of short‐term exercise training in vivo.MethodsWe used 31P‐magnetic resonance spectroscopy (31P‐MRS) to examine the effect of short‐term plantar flexion exercise training on phosphocreatine (PCr) recovery kinetics and the control of respiration rate. To this aim, we investigated 12 healthy men experienced with this exercise modality (TRA) and 8 time‐control subjects (TC).ResultsAfter 5 days of training, maximum work rate during incremental plantar flexion exercise was significantly improved (P &lt; 0.01). During the recovery period, the maximal rate of oxidative ATP synthesis (PRE: 28 ± 13 mM.min−1; POST: 26 ± 15 mM.min−1) and the PCr recovery time constant (PRE: 31 ± 19 s; POST: 29 ± 16) were not significantly altered. In contrast, the Hill coefficient (nH) describing the cooperativity between respiration rate and ADP was significantly increased in TRA (PRE:nH =2.7 ± 1.4; POST: nH =3.4 ± 1.9, P &lt; 0.05). Meanwhile, we did not observe any systematic variation in any of these variables in the TC.ConclusionThis study reveals that 5 days of training induces rapid adaptation in the allosteric control of respiration rate by ADP before any substantial improvement in muscle oxidative capacity.

Exercise‐induced PCr recovery kinetics and tissue oxygenation: The role of free radicals and aging

We investigated the role of free radicals on muscle oxidative capacity and O2 availability in activity matched young (Y) and old (O) people following exercise. 39 subjects (19 Y and 20 O) performed sub‐maximal plantar flexion exercise following the consumption of either a placebo (PL) or an antioxidant (AO) cocktail. PCr resynthesis was assessed by 31P‐MRS (magnetic resonance spectroscopy), while muscle re‐oxygenation and limb blood flow were evaluated by near‐infrared spectroscopy and ultrasound Doppler, respectively. The PCr recovery time constant in O (PL: 37 ± 6; AO: 38 ± 6 s) and Y (PL: 38 ± 6; AO: 36 ± 4 s) as well as the maximal rate of oxidative ATP synthesis in O (PL: 15 ± 2; AO: 14 ± 2 mM.min−1) and Y (PL: 13 ± 2; AO: 15 ± 3 mM.min−1) were not altered by age or AO. In contrast, muscle reoxygenation rate, although not affected by age, was slower in the Y following AO, as evidenced by the time constant (P &lt; 0.05) and mean response time (PL: 49 ± 6; AO: 70 ± 10 s) of deoxy‐Hb recovery, while no difference was observed in the old. These data reveal that, when subjects are activity matched, muscle oxidative capacity is preserved with age. In addition, unlike the O, the compromising effect of the AO on O2 availability in the microcirculation of the Y, without affecting PCr recovery kinetics, implies that free radicals play a role in blood flow regulation and that O2 availability exceeds mitochondrial capacity in this population.

Allocryptopine and benzyltetrahydropalmatine block hERG potassium channels expressed in HEK293 cells

Allocryptopine (ALL) is an alkaloid extracted from Corydalis decumbens (Thunb) Pers. Papaveraceae, whereas benzyltetrahydropalmatine (BTHP) is a derivative of tetrahydropalmatine extracted from Corydalis ambigua (Pall) Cham et Schlecht. The aim of this study was to investigate the effects of ALL and BTHP on the human ether-a-go-go related gene (hERG) current expressed in HEK293 cells. Cultured HEK293 cells were transiently transfected with hERG channel cDNA plasmid pcDNA3.1 using Lipofectamine. The whole-cell current IHERG was evoked and recorded using Axon MultiClamp 700B amplifier. The drugs were applied via supserfusion. Both ALL and BTHP reversibly suppressed the amplitude and density of IHERG in concentration- and voltage-dependent manners (the respective IC50 value was 49.65 and 22.38 μmol/L). BTHP (30 μmol/L) caused a significant negative shift of the steady-state inactivation curve of IHERG, while ALL (30 μmol/L) did not affect the steady-state inactivation of IHERG. Furthermore, BTHP, but not ALL, shortened the time constants of fast inactivation and slow time constants of deactivation of IHERG. But both the drugs markedly lengthened the time constants for recovery of IHERG from inactivation. Using action potential waveform pulses, it was found that both the drugs at 30 μmol/L significantly suppressed the current densities in the late phase of action potential, but did not significantly affect the current densities in the early phase of action potential. Both ALL and BTHP derived from Chinese herbs potently block hERG current.

Different Metabolic Responses during Incremental Exercise Assessed by Localized 31P MRS in Sprint and Endurance Athletes and Untrained Individuals

Until recently, assessment of muscle metabolism was only possible by invasive sampling. 31P magnetic resonance spectroscopy (31P MRS) offers a way to study muscle metabolism non-invasively. The aim of the present study was to use spatially-resolved 31P MRS to assess the metabolism of the quadriceps muscle in sprint-trained, endurance-trained and untrained individuals during exercise and recovery. 5 sprint-trained (STA), 5 endurance-trained (ETA) and 7 untrained individuals (UTI) completed one unlocalized 31P MRS session to measure phosphocreatine (PCr) recovery, and a second session in which spatially-resolved 31P MR spectra were obtained. PCr recovery time constant (τ) was significantly longer in STA (50±17 s) and UTI (41±9 s) than in ETA (30±4 s), (P<0.05). PCr changes during exercise differed between the groups, but were uniform across the different components of the quadriceps within each group. pH during recovery was higher for the ETA than for the UTI (P<0.05) and also higher than for the STA (P<0.01). Muscle volume was greater in STA than in UTI (P<0.05) but not different from ETA. Dynamic 31P MRS revealed considerable differences among endurance and sprint athletes and untrained people. This non-invasive method offers a way to quantify differences between individual muscles and muscle components in athletes compared to untrained individuals.

Recovery of vesicular storage and release parameters after high frequency stimulation in rat hippocampus

The replenishment rates estimated from the recovery of synaptic efficacy following synaptic depression are known to be widely scattered. Given the importance of the replenishment during stimulation, especially if it is prolonged, it is important to better understand what influences the recovery of the synaptic efficacy following stimulation. We fit a two-pool model of vesicular secretion to the changes of the excitatory post-synaptic currents recorded in CA1 neurons of rat hippocampal slices to determine how the model parameters change during, and following, long stimulation. The replenishment rate at the end of stimulation inducing synaptic depression differs greatly from that at the beginning of stimulation. It decreases progressively and rapidly (by ~75% and with a time constant of <10s) during stimulation, and this is followed by a similarly fast recovery (time constant of ~10s), but to a steady-state that is approximately twice as large as its pre-stimulation value. Both [Ca(++)]o and the duration of long stimulation influence the recovery of the replenishment rate. Its new steady-state is significantly higher, if either [Ca(++)]o is higher or stimulation longer, but the recovery of the replenishment rate becomes clearly slower if [Ca(++)]o is higher, and faster if stimulation is longer. Many factors thus influence the recovery of the replenishment rate and of the synaptic efficacy, but the stimulation induced [Ca(++)]i accumulation cannot explain the change of the replenishment rate during recovery. Finally, okadaic acid, which speeds up vesicular trafficking, does not alter the recovery of the replenishment rate. The vesicular replenishment of the RRP following stimulation is thus not likely to be associated with significant vesicular movement.

Vascular Endothelial Growth Factor Modulates Voltage-Gated Na+ Channel Properties and Depresses Action Potential Firing in Cultured Rat Hippocampal Neurons

Vascular endothelial growth factor (VEGF), an angiogenic factor, was found to modulate synaptic plasticity by affecting K(+) and Ca(2+) channels and protect neuron from death by depressing glutamatergic transmission. However, whether VEGF also modulates neuronal activity through modulating voltage-gated Na(+) channels (VGSCs), a main determinant of neuronal excitability, we observed the effects of VEGF on Na(+) channel properties and function on cultured rat hippocampal neurons through whole-cell patch-clamp recording. We found that VEGF decreased the Na(+) channel excitability by shifting the voltage-dependence of steady-state inactivation to more hyperpolarized direction, and increasing the time constants of recovery from inactivation without significantly affecting the activation process. The effect of VEGF on Na(+) channel steady-state inactivation was inhibited by the specific VEGF Flk-1 receptor antagonist SU1498, but was not affected by protein kinase C (PKC)-activator 1-oleoyl-2-acetyl-sn-glycerol (OAG). Furthermore, the inhibition of Na(+) currents by VEGF was frequency-dependent. In addition, the frequency of neuron firing evoked by current injection was reversibly depressed by VEGF. Therefore, our results suggest a potential role of VGSCs in the modulation of VEGF on neuronal excitability.

Evaluation of glutamate concentration transient in the synaptic cleft of the rat calyx of Held

Establishing the spatiotemporal concentration profile of neurotransmitter following synaptic vesicular release is essential for our understanding of inter-neuronal communication. Such profile is a determinant of synaptic strength, short-term plasticity and inter-synaptic crosstalk. Synaptically released glutamate has been suggested to reach a few millimolar in concentration and last for <1 ms. The synaptic cleft is often conceived as a single concentration compartment, whereas a huge gradient likely exists. Modelling studies have attempted to describe this gradient, but two key parameters, the number of glutamate in a vesicle (N(Glu)) and its diffusion coefficient (D(Glu)) in the extracellular space, remained unresolved. To determine this profile, the rat calyx of Held synapse at postnatal day 12-16 was studied where diffusion of glutamate occurs two-dimensionally and where quantification of AMPA receptor distribution on individual postsynaptic specialization on medial nucleus of the trapezoid body principal cells is possible using SDS-digested freeze-fracture replica labelling. To assess the performance of these receptors as glutamate sensors, a kinetic model of the receptors was constructed from outside-out patch recordings. From here, we simulated synaptic responses and compared them with the EPSC recordings. Combinations of N(Glu) and D(Glu) with an optimum of 7000 and 0.3 μm(2) ms(-1) reproduced the data, suggesting slow diffusion. Further simulations showed that a single vesicle does not saturate the synaptic receptors, and that glutamate spillover does not affect the conductance amplitude at this synapse. Using the estimated profile, we also evaluated how the number of multiple vesicle releases at individual active zones affects the amplitude of postsynaptic signals.

The influence of age on the recovery of the ERG photostress test

Focal ERG associated with photostress test could be a useful diagnostic method for evaluating macular visual function. The main aim of this study was to evaluate the effect of age on the recovery time constant of the ERG photostress test. The second aim was to assess the sources of variability which affect the measurements. Fifty-four healthy subjects (108 eyes), aged between 21 and 77, with corrected VA of 20/20 or more and absence of any ocular or systemic disease, were recruited. For each eye ERG response to focal (20° in diameter) 42-Hz stimulation was recorded: three series of 200 summations in base conditions and a six series of 42-Hz ERGs (100 summations each) at 10, 40, 80, 180, 300 and 420 s after bleaching by a white spot of light (20° in diameter) from a direct ophthalmoscope (800 cd/m²) pointed at macular region for 30 s. Fourier analysis was performed and amplitude of the first harmonica calculated. The relationship of basal amplitudes with subject age and gender, and the kinetics of macular function recovery were assessed through mixed-effects models. Mean basal amplitude decreases by 0.046 μV for year of life. The recovery after bleaching is proportional to age with an increase of 4.31 s for decade. Restoration of amplitude is slower in older subjects. There is a significant decrease in macular ERG amplitude with age. The macular recovery after photostress shows exponential kinetics that are less efficient in older subjects: this could be related to lower effectiveness of photopigment restoration in advanced age.

Exercise efficiency is reduced by mitochondrial uncoupling in the elderly

A reduction in exercise efficiency accompanies ageing in humans. Here we evaluated the impact of changes in the contractile-coupling and mitochondrial-coupling efficiencies on the reduction in exercise efficiency in the elderly. Nine adult (mean, 38.8 years old) and 40 elderly subjects (mean, 68.8 years old) performed a cycle ergometer test to measure O2 uptake and leg power output up to the aerobic limit ( ). Reduced leg power output per unit O2 uptake was reflected in a drop in delta efficiency (εD) from 0.27 ± 0.01 (mean ± SEM) in adults to 0.22 ± 0.01 in the elderly group. Similar declines with age were apparent for both the leg power output at and the ATP generation capacity (ATPmax) determined in vivo using (31)P magnetic resonance spectroscopy. These similar declines resulted in unchanged contractile-coupling efficiency values (εC) in the adult (0.50 ± 0.05) versus the elderly group (0.58 ± 0.04) and agreed with independent measures of muscle contractile-coupling efficiency in human quadriceps (0.5). The mitochondrial-coupling efficiency calculated from the ratio of delta to contractile-coupling efficiencies in the adults (εD/εC = 0.58 ± 0.08) corresponded to values for well-coupled mitochondria (0.6); however, εD/εC was significantly lower in the elderly subjects (0.44 ± 0.03). Conversion of ATPmax per mitochondrial volume (ATPmax/Vv[mt,f]) reported in these groups into thermodynamic units confirmed this drop in mitochondrial-coupling efficiency from 0.57 ± 0.08 in adults to 0.41 ± 0.03 in elderly subjects. Thus, two independent methods revealed that reduced mitochondrial-coupling efficiency was a key part of the drop in exercise efficiency in these elderly subjects and may be an important part of the loss of exercise performance with age.

Variation in sodium current amplitude between vasopressin and oxytocin hypothalamic supraoptic neurons

Biophysical characteristics of tetrodotoxin-sensitive sodium (Na(+)) currents were studied in vasopressin (VP) and oxytocin (OT) supraoptic neurons acutely isolated from rat hypothalamus. Na(+) current density (pA/pF) was significantly greater in VP neurons than in OT neurons. No significant difference between VP and OT neurons was detected regarding the voltage dependence of activation and steady-state inactivation, or rate of recovery from inactivation of Na(+) currents. In both VP and OT neurons, the macroscopic inactivation of the Na(+) currents was best fitted with a double-exponential expression suggesting two rates of inactivation. Also in both types, the time course of recovery from inactivation proceeded with fast and slow time constants averaging around 8 and 350 ms, respectively, suggesting the presence of multiple pathways of recovery from inactivation. The slower time constant of recovery of inactivation may be involved in the decrease in action potential (AP) amplitude that occurs after the first spike during burst firing in both neuronal types. The larger amplitude of Na(+) currents in VP vs. OT neurons may explain the previous observations that VP neurons exhibit a lower AP threshold and greater AP amplitude than OT neurons, and may serve to differently tune the firing properties and responses to neuromodulators of the respective neuronal types.

Heart Rate Recovery Is Impaired After Maximal Exercise Challenge in Pediatric Sickle Cell Anemia

AbstractAbstract ▪3220▪This icon denotes a clinically relevant abstractSlow heart rate recovery (HRR) after exercise, particularly at 1 and 2 minutes during recovery, is a strong indicator of autonomic nervous system (ANS) imbalance and represents an important risk factor for increased cardiovascular morbidity and mortality in the general population. Recent evidence suggests cardiovascular ANS dysfunction and vagal tone impairment also exist in individuals with sickle cell anemia (SCA). Despite the known impact of disease burden on exercise capacity and overall fitness in SCA, post-exercise HRR has not previously been studied in this population. The objective of this study was to examine HRR in the post-exercise recovery phase following maximal exercise testing in a cohort of children and young adults with SCA. Methods We prospectively performed maximal cardiopulmonary exercise testing using a ramp, cycle ergometry protocol in 60 subjects with SCA (hemoglobin SS and S-β0 thalassemia) and 20 controls without SCA or sickle cell trait matched for race and gender. Data from standard 12-lead electrocardiography (ECG) was assessed during a 10-minute recovery phase, and HR and corrected QT (QTc) interval measured from tracings obtained at 1-minute intervals. A single investigator performed all measurements manually using leads II, V5, and V6. Final values were averaged from 3 independent measurements. The difference between maximal HR and both HR at 1-minute (ΔHR1min) and 2-minute (ΔHR2min) recovery was our primary outcome. Between-group differences were compared using Mann-Whitney U testing (IBM, SPSS V20). The relationship between ΔHR1min and exercise parameters was examined using Spearman’s rank correlation coefficient. Results Post-exercise ECG data from 58 subjects with SCA (median age 15.5 years) and 20 controls without SCA (median age 12 years) were interpretable for this analysis. A total of 30/58 (52%) and 22/58 (38%) subjects were male and on hydroxyurea, respectively. There was no significant difference in median baseline HR or QTc interval in subjects versus controls. Median peak HR was also not significantly different in the 2 groups. When compared to controls, subjects with SCA demonstrated significantly lower HR reserve (100 vs. 111 bpm, p = 0.005), representing the difference between peak and baseline HR. Impaired HRR, defined by slower declines in HR during recovery, was also evident among subjects with SCA following maximal exercise challenge. Although the absolute HR measured at each minute of recovery did not differ significantly in the 2 groups, subjects demonstrated significantly smaller median ΔHR1min (21 vs. 33 bpm, p < 0.0001) and ΔHR2min (39 vs. 51 bpm, p = 0.003), even after adjustment for age between groups. Significantly smaller ΔHR values were also noted in subjects at each minute up to 8 minutes throughout recovery. When compared to subjects not on hydroxyurea, subjects on treatment had significantly greater median ΔHR1min (25 vs. 19 bpm, p = 0.037) but similar ΔHR2min. In subjects with SCA, ΔHR1min correlated inversely with age (−0.41, p = 0.001) and directly with peak oxygen consumption (peak VO2) (0.30, p = 0.03) and oxygen delivery (ΔVO2/Δwork rate) (0.46, p < 0.0001), but not with baseline QTc interval or hemoglobin. Through mono-exponential curve fitting, we found that the time constant associated with HR decline over the first 5 minutes of recovery was greater in subjects with SCA versus controls (T = 128 sec, 95% CI [123, 134] versus 104 sec, 95% [97, 110]). Conclusions Compared to controls without SCA, children and young adults with SCA demonstrate impaired HRR following maximal cardiopulmonary exercise testing, as evidenced by smaller decrements in HR at 1 and 2 minutes during recovery and exponential time constants that indicate a longer period of time over which HR declines. Slower HRR is also associated with decreased fitness and measures of oxygen delivery during exercise testing in subjects with SCA. Although the mechanisms are not well understood, prolonged HRR in this population may in part be explained by ANS imbalance, suggesting either inadequate sympathetic withdrawal or suboptimal parasympathetic reactivation in the post-exercise period. Future studies should focus on delineating the role of the ANS in post-exercise HRR and assessing the prognostic potential of this marker as it relates to disease severity and outcomes in SCA. Disclosures:No relevant conflicts of interest to declare.

The inhibitory effect of curcumin on voltage-dependent K+ channels in rabbit coronary arterial smooth muscle cells

We investigated the effects of curcumin, the principal active compound of turmeric, on voltage-dependent K(+) (Kv) channels in freshly isolated rabbit coronary arterial smooth muscle cells using the voltage-clamp technique. Curcumin reduced the Kv current in a dose-dependent manner with an apparent K(d) value of 1.07 ± 0.03 μM. Although curcumin did not alter the kinetics of Kv current activation, it predominantly accelerated the decay rate of channel inactivation. The association and dissociation rate constants of curcumin were 1.35 ± 0.05 μM(-1)s(-1) and 1.47 ± 0.17s(-1), respectively. Curcumin did not alter the steady-state activation or inactivation curves. Application of train pulses (1 or 2 Hz) increased curcumin-induced blockade of the Kv current, and the recovery time constant also increased in the presence of curcumin suggesting, that the inhibitory action of Kv currents by curcumin was use-dependent. From these results, we concluded that curcumin inhibited vascular Kv current in a state-, time-, and use-dependent manner.

TRPV1 properties in thoracic dorsal root ganglia neurons are modulated by intraperitoneal capsaicin administration in the late phase of type-1 autoimmune diabetes.

Pharmacological therapies in type 1 diabetes for efficient control of glycemia and changes in pain alterations due to diabetic neuropathy are a continuous challenge. Transient receptor potential vanilloid type 1 (TRPV1) from dorsal root ganglia (DRG) neurons is one of the main pharmacological targets in diabetes, and its ligand capsaicin can be a promising compound for blood-glucose control. Our goal is to elucidate the effect of intraperitoneal (i.p.) capsaicin administration in type 1 diabetic mice against TRPV1 receptors from pancreatic DRG primary afferent neurons. A TCR(+/-)/Ins-HA(+/-) diabetic mice (dTg) was used, and patch-clamp and immunofluorescence microscopy measurements have been performed on thoracic T(9)-T(12) DRG neurons. Capsaicin (800 μg/kg, i.p. three successive days) administration in the late-phase diabetes reduces blood-glucose levels, partly reverses the TRPV1 current density and recovery time constant, without any effect on TRPV1 expression general pattern, in dTg mice. A TRPV1 hypoalgesia profile was observed in late-phase diabetes, which was partly reversed to normoalgesic profile upon capsaicin i.p. administration. According to the soma dimensions of the thoracic DRG neurons, a detailed analysis of the TRPV1 expression upon capsaicin i.p. treatment was done, and the proportion of large A-fiber neurons expressing TRPV1 increased in dTg capsaicin-treated mice. In conclusion, the benefits of low-dose capsaicin intraperitoneal treatment in late-phase type-1 diabetes should be further exploited.

Measurement and analysis of the shape recovery process of each erythrocyte for estimation of its deformability using the microchannel technique: the influence of the softness of the cell membrane and viscosity of the hemoglobin solution inside the cell

This study tried to evaluate the deformability of each erythrocyte by measuring the time constant of shape recovery just after the erythrocytes left the microchannels. We fabricated a microchannel array with a 5μm-square, 100μm-long cross-section on a PDMS sheet. Three different kinds of blood samples were prepared—healthy erythrocytes as a control, artificially membrane-hardened erythrocytes and artificial hemoglobin solution-diluted erythrocytes—to investigate the influence of erythrocyte's mechanical property changes on the time constant of shape recovery. These shape recovery processes were modeled and analyzed by a standard liner solid model. As a result, the temporal variation of the compressive strain of all erythrocytes showed exponential decay with time elapsed like a first order lag system, so the time constant of shape recovery could be calculated from the semi-logarithmic relaxation curve. The stiffer the cell membrane was using glutaraldehyde, the shorter the time constant for relaxation became compared to healthy erythrocytes. The diluted hemoglobin erythrocytes snapped back quicker than healthy ones. In addition, the time constant of healthy blood drawn from females was clearly shorter than that collected from males. However, the time constant of fully hemoglobin substituted erythrocytes was not affected by gender difference. These results indicate that there is not a significant difference in the stiffness of healthy cell membranes regardless of individual and gender differences. On the other hand, the viscosity of the hemoglobin solution inside the cell is one of the significant factors affecting the time constant. Therefore, these results suggest that the deformability of individual erythrocytes can be quantitated by the time constant for relaxation measured by microchannel techniques.