Metabolic rates of minke whales (Balaenoptera acutorostrata) in cold water

Body temperature, blubber thickness and lung capacity (V_e) were recorded in newly killed minke whales, while respiratory frequency (f) was determined in free-swimming animals. Mean deep (thoracic) body temperature was 34.7±0.8 (SD) °C (n= 14). Weighted mean core/blubber interface temperature in animals caught in 2.5-5.5 °C water was 28.8±1.7 °C (n= 8). The minimum average rate of sensible heat loss (HL_s) was 3.81±0.53 (SD) W kg_w^-0.75 (n= 8) in animals with body masses (w) in the range of 1840 to 5740 kg, HL_s being inversely proportional to ω (HL_S= - 2.98 10^-4 w + 4.89 W kgω^{-0 75} (n= 8, r^-2= 0.73, P < 0.01)). The average rate of respiratory heat loss (HL_r) was 0.26±0.04 (SD) W kg_w^-0.75, regardless of w, in the same 8 animals. Total rates of heat loss (HL=HL_r+HL_s) in 2.5-5.5 °C water ranged between 3.40 and 4.87 W kg_w^-0.75, with an average of 4.06±0.52 (SD) W kg_w^-0.75 (n= 8). Estimates of oxygen consumption based on records of f and V_c and data on oxygen extraction from other cetaceans, yielded a range of metabolic rates which compared nicely with the calculated HL values.     

Blood oxygenation level-dependent (BOLD) total and extravascular signal changes and ΔR2* in human visual cortex at 1.5, 3.0 and 7.0 T

The characterisation of the extravascular (EV) contribution to the blood oxygenation level‐dependent (BOLD) effect is important for understanding the spatial specificity of BOLD contrast and for modelling approaches that aim to extract quantitative metabolic parameters from the BOLD signal. Using bipolar crusher gradients, total (b = 0 s/mm²) and predominantly EV (b = 100 s/mm²) gradient echo BOLD ΔR₂* and signal changes (ΔS/S) in response to visual stimulation (flashing checkerboard; f = 8 Hz) were investigated sequentially (within < 3 h) at 1.5, 3.0 and 7.0 T in the same subgroup of healthy volunteers (n = 7) and at identical spatial resolutions (3.5 × 3.5 × 3.5 mm³). Total ΔR₂* (z‐score analysis) values were ?0.61 ± 0.10 s^?1 (1.5 T), ?0.74 ± 0.05 s^?1 (3.0 T) and ?1.37 ± 0.12 s^?1 (7.0 T), whereas EV ΔR₂* values were ?0.28 ± 0.07 s^?1 (1.5 T), ?0.52 ± 0.07 s^?1 (3.0 T) and ?1.25 ± 0.11 s^?1 (7.0 T). Although EV ΔR₂* increased linearly with field, as expected, it was found that EV ΔS/S increased less than linearly with field in a manner that varied with TE choice. Furthermore, unlike ΔR₂*, total and EV ΔS/S did not converge at 7.0 T. These trends were similar whether a z‐score analysis or occipital lobe‐based region‐of‐interest approach was used for voxel selection. These findings suggest that calibrated BOLD approaches may benefit from an EV ΔR₂* measurement as opposed to a ΔS/S measurement at a single TE. Copyright © 2010 John Wiley & Sons, Ltd.     

Middle cerebral artery blood velocity during exercise with β‐1 adrenergic and unilateral stellate ganglion blockade in humans

A reduced ability to increase cardiac output (CO) during exercise limits blood flow by vasoconstriction even in active skeletal muscle. Such a flow limitation may also take place in the brain as an increase in the transcranial Doppler determined middle cerebral artery blood velocity (MCA V_mean) is attenuated during cycling with β‐1 adrenergic blockade and in patients with heart insufficiency. We studied whether sympathetic blockade at the level of the neck (0.1% lidocain; 8 mL; n=8) affects the attenuated exercise – MCA V_mean following cardio‐selective β‐1 adrenergic blockade (0.15 mg kg^?1 metoprolol i.v.) during cycling. Cardiac output determined by indocyanine green dye dilution, heart rate (HR), mean arterial pressure (MAP) and MCA V_mean were obtained during moderate intensity cycling before and after pharmacological intervention. During control cycling the right and left MCA V_mean increased to the same extent (11.4 ± 1.9 vs. 11.1 ± 1.9 cm s^?1). With the pharmacological intervention the exercise CO (10 ± 1 vs. 12 ± 1 L min^?1; n=5), HR (115 ± 4 vs. 134 ± 4 beats min^?1) and ΔMCA V_mean (8.7 ± 2.2 vs. 11.4 ± 1.9 cm s^?1) were reduced, and MAP was increased (100 ± 5 vs. 86 ± 2 mmHg; P < 0.05). However, sympathetic blockade at the level of the neck eliminated the β‐1 blockade induced attenuation in ΔMCA V_mean (10.2 ± 2.5 cm s^?1). These results indicate that a reduced ability to increase CO during exercise limits blood flow to a vital organ like the brain and that this flow limitation is likely to be by way of the sympathetic nervous system.     

A diazo-2 study of relaxation mechanisms in frog and barnacle muscle fibres: effects of pH, MgADP, and inorganic phosphate

 The aim of this study was to compare the effects of increased concentrations of MgADP, inorganic phosphate (P_i) and H⁺ ([MgADP], [Pi] and [H⁺], respectively) on the rate of relaxation in two different muscle types: skinned muscle fibres from the frog Rana temporaria and myofibrillar bundles from the giant Pacific acorn barnacle Balanus nubilus. Relaxation transients are produced by the photolysis of diazo-2 and are well fitted with a double exponential curve, giving two rate constants: k₁ [5.6±0.1 s^–1 for barnacle, n=30; 26.3±0.7 s^–1 for frog, n=14 (mean±SEM)] and k₂ [0.6±0.1 s^–1 in barnacle, n=30; 10.4±1.0 s^–1 in frog, n=14 (mean±SEM)], at 10°C. Decreasing the pH by 0.5 pH units did not significantly affect k₁ for barnacle relaxation [5.6±0.1 s^–1 (mean±SEM), n=15] compared to the decrease in k₁ of 40% seen in frog. Use of the Ca²⁺-sensitive fluorescent label acrylodan on barnacle wild-type troponin C demonstrated that decreasing the pH from 7.0 to 6.6 only alters the pCa₅₀ value by 0.23 in the cuvette, while stopped-flow experiments with acrylodan revealed no significant change in k_off from the labelled protein [322±32 s^–1 at pH 7.0 and 381±24 s^–1 (mean±SEM) at pH 6.6]. Increasing [MgADP] by 20 μM (50 μM added ADP) from control values of 50 μM in frog decreased k₁ to 12.3±0.4 s^–1 (mean±SEM, n=8), and at 400 μM MgADP, k₁=9.6±0.1 s^–1 (mean±SEM, n=12). In barnacle, 500 μM MgADP had a much smaller effect on k₁ (4.0±0.9 s^–1, mean±SEM, n=8). Increasing the free [P_i] from the contaminant level of 0.36 mM to 1.9 mM slowed k₁ by ≈15% in barnacle [4.8±0.8 s^–1, mean±SEM, n=7], compared to a ≈30% reduction seen in frog. We conclude that the differences between barnacle and frog seen here are most probably due to different isomers of the contractile proteins, and that events underlying the crossbridge cycle are the same or similar. We interpret our results according to a model of crossbridge transitions during relaxation. Received: 18 May 1998 / Received after revision and accepted: / 1 September 1998     

Obesity and catecholamine responses to maximal exercise in adolescent girls

The aim of this study was to investigate plasma catecholamine [adrenaline (A) and noradrenaline (NA)] concentrations at rest and in response to maximal exercise in three different groups of adolescent girls. According to their body mass index, 34 adolescent girls aged 15–16 years were divided into three groups: a normal weight group (NO) (n = 11), an overweight group (OW) (n = 11) and an obese group (OB) (n = 12). Plasma A and NA concentrations were measured at rest during fasting conditions (A ₀ and NA₀), after a standardized breakfast (A _rest and NA_rest) and immediately after an incremental exhaustive exercise (A _EX and NA_EX). A ₀ and NA₀ were not significantly different among the three groups. However, the A ₀/NA₀ was statistically lower in OB compared to OW and NO. A _EX and NA_EX were significantly higher than resting values in the three groups. However, in response to exercise, no significant differences were reported between OB (A _EX = 2.20 ± 0.13 nmol/l, NA_EX = 12.28 ± 0.64 nmol/l), OW (A _EX = 2.39 ± 0.23 nmol/l, NA_EX = 12.94 ± 0.93 nmol/l) and NO (A _EX = 2.52 ± 0.24 nmol/l, NA_EX = 12.60 ± 0.63 nmol/l). In conclusion, our results showed that at rest, in adolescent girls, the responsiveness of the adrenal medulla to the sympathetic nervous activity is lower in OB subjects compared to OW and NO ones. However, in response to maximal exercise, plasma catecholamines are not affected by obesity.     

The influence of PaO2, pH and SaO2 on maximal oxygen uptake

Influence of arterial oxygen pressure (P_aO₂) and pH on haemoglobin saturation (S_aO₂) and in turn on O₂ uptake (VO ₂) was evaluated during ergometer rowing (156, 276 and 376 W; VO _2max, 5.0 L min^?1; n = 11). During low intensity exercise, neither pH nor S_aO₂ were affected significantly. In response to the higher work intensities, ventilations (V_E) of 129 ± 10 and 155 ± 8 L min^?1 enhanced the end tidal PO₂ (P_ETO₂) to the same extent (117 ± 2 mmHg), but P_aO₂ became reduced (from 102 ± 2 to 78 ± 2 and 81 ± 3 mmHg, respectively). As pH decreased during maximal exercise (7.14 ± 0.02 vs. 7.30 ± 0.02), S_aO₂ also became lower (92.9 ± 0.7 vs. 95.1 ± 0.1%) and arterial O₂ content (C_aO₂) was 202 ± 3 mL L^?1. An inspired O₂ fraction (F_IO₂) of 0.30 (n = 8) did not affect V_E, but increased P_ETO₂ and P_aO₂ to 175 ± 4 and 164 ± 5 mmHg and the P_ETO₂–P_aO₂ difference was reduced (21 ± 4 vs. 36 ± 4 mmHg). pH did not change when compared with normoxia and S_aO₂ remained within 1% of the level at rest in hyperoxia (99 ± 0.1%). Thus, C_aO₂ and VO _2max increased to 212 ± 3 mL L^?1 and 5.7 ± 0.2 L min^?1, respectively. The reduced P_aO₂ became of importance for S_aO₂ when a low pH inhibited the affinity of O₂ to haemoglobin. An increased F_IO₂ reduced the gradient over the alveolar-arterial membrane, maintained haemoglobin saturation despite the reduction in pH and resulted in increases of the arterial oxygen content and uptake.     

Serum eosinophil peroxidase (EPO) levels in asthmatic patients

Eosinophil granular proteins are a useful eosinophilic activation marker in asthmatic patients. In this study, the eosinophil peroxidase (EPO) levels were assessed in different stages of bronchial asthma, in 123 patients suffering from asthma, classified as mild (n=49), moderate (n=49), and severe (n=25), according to the International Consensus Report on Diagnosis and Treatment of Asthma, as well as in 27 healthy controls, with the aim of evaluating the importance of this protein as a severity marker in bronchial asthma, and its possible correlation with parameters such as anamnesis, respiratory function tests, and peripheral blood eosinophil count, and also with some allergologic diagnostic tests, both in vivo and in vitro. The geometric mean serum level of EPO was 9.3±11.3 ng/ml (median±SD) in controls, and 28±37.8 ng/ml in the asthmatic patients. Depending on the asthma severity, the EPO levels were 25±30.5; 29±37.1, and 41 ±47.3 ng/ml in mild, moderate, and severe asthmatics, respectively, being the significant differences between the group of patients with mild and severe asthma (P<0.001). The number of eosinophils (eos) in peripheral blood was 157±20 eos/mm³ in the controls, 334+35 eos/mm³ in mild asthmatics, 510 ±87 eos/mm³ in moderate asthmatics, and 658±72 eos/mm³ in severe asthmatics, with significant differences between all the groups (from P<0.05 to P<0.001). Both the serum levels of EPO and the number of eosinophils were greater in patients with active asthma than in patients with inactive asthma (P<0.001). Significant negative correlations (P < 0.001) were found between serum levels of EPO and FEY, (r_s= 0.30), MEF_25-75 (r_s= -0.33), and MEF₅₀ (r_s= -0.34), and a good positive correlation (r_s= 0.80, P<0.001) was found between EPO levels and the number of eosinophils in peripheral blood. We also found a significant positive correlation between eosinophil number and clinical score (r_s= 0.54, P<0.001) and between EPO levels and the mentioned score (r_s= 0.46, P<0.001).     

Reduced coronary reserve in response to short-term ischaemia and vasoactive drugs in ex vivo hearts from diabetic mice

Aim: The aim of the present study was to compare the coronary flow (CF) reserve of ex vivo perfused hearts from type 2 diabetic (db/db) and non‐diabetic (db/+) mice. Methods: The hearts were perfused in the Langendorff mode with Krebs–Henseleit bicarbonate buffer (37 °C, pH 7.4) containing 11 mmol L^?1 glucose as energy substrate. The coronary reserve was measured in response to three different interventions: (1) administration of nitroprusside (a nitric oxide donor), (2) administration of adenosine and (3) production of reactive hyperaemia by short‐term ischaemia. Results: Basal CF was approximately 15% lower in diabetic when compared with non‐diabetic hearts (2.1 ± 0.1 vs. 2.6 ± 0.2 mL min^?1). The maximum increase in CF rate in response to sodium nitroprusside and adenosine was significantly lower in diabetic (0.6 ± 0.1 and 0.9 ± 0.1 mL min^?1 respectively) than in non‐diabetic hearts (1.2 ± 0.1 and 1.4 ± 0.1 mL min^?1 respectively). Also, there was a clear difference in the rate of return to basal CF following short‐term ischaemia between diabetic and non‐diabetic hearts. Thus, basal tone was restored 1–2 min after the peak hyperaemic response in non‐diabetic hearts, whereas it took approximately 5 min in diabetic hearts. Conclusion: These results show that basal CF, as well as the CF reserve, is impaired in hearts from type 2 diabetic mice. As diabetic and non‐diabetic hearts were exposed to the same (maximum) concentrations of NO or adenosine, it is suggested that the lower coronary reserve in type 2 diabetic hearts is, in part, because of a defect in the intracellular pathways mediating smooth muscle relaxation.     

Calcium and calcimimetics regulate paracellular Na+ transport in the thin ascending limb of Henle’s loop in mouse kidney

The effect of Ca²⁺ and calcimimetics on NaCl transport was investigated in the in vitro isolated microperfused mouse thin ascending limb of Henle’s loop. In the presence of a transmural NaCl gradient, the transepithelial diffusional potential was 13.7?±?0.4 mV (n?=?17). When the Ca²⁺ in the bath was increased from 1.5 to 4.5 mM at 37°C, the relative permeability of Na⁺ to Cl^? (P _Na /P _Cl) estimated from the diffusional voltage deflection due to the transepithelial NaCl gradient (V _d) changed from 0.371?±?0.017 to 0.341?±?0.015 (n?=?10, P?<?0.0001). When the Ca²⁺ in the lumen was increased from 1.5 to 4.5 mM, the P _Na /P _Cl decreased from 0.349?±?0.013 to 0.330?±?0.013 (n?=?5, P?<?0.002). The addition of 0.1 mM neomycin and 0.2 mM gentamicin to the bath or lumen also decreased the P _Na /P _Cl. The same effect on P _Na /P _Cl of Ca²⁺ and calcimimetics occurred in ClC-K1 (kidney-specific chloride channel) knockout mice. The addition of 300 μg/ml protamine to the bath strongly inhibited changes to P _Na /P _Cl induced by basolateral Ca²⁺. These data indicate that ambient Ca²⁺ and calcimimetics inhibit Na⁺ transport in the thin ascending limb, which is known to occur via the paracellular shunt pathway. Our observations strongly suggest that Ca²⁺ is involved in the regulation of paracellular Na⁺ permeability in the thin ascending limbs.     

EPR Investigations into the Kinetics of Trithiocarbonate‐Mediated RAFT‐Polymerization of Butyl Acrylate

Electron paramagnetic resonance (EPR) spectroscopy is used for measuring rate coefficients of addition, k_ad, and fragmentation, k_β, together with the associated equilibrium constants, K_eq, for butyl acrylate polymerizations mediated by S‐ethyl propan‐2‐ylonate‐S’‐propyl trithiocarbonate (EPPT) and by S‐S’‐bis(methyl‐2‐propionate) trithiocarbonate (BMPT). Experiments at ?40 °C yield k_ad = (3.4 ± 0.3) × 10⁶ L mol^?1 s^?1, k_β = (1.4 ± 0.4) × 10² s^?1, and K_eq = (2.6 ± 0.8) × 10⁴ L mol^?1 for EPPT and k_ad = (4.1 ± 0.9) × 10⁶ L mol^?1 s^?1, k_β = (4.5 ± 0.5) × 10¹ s^?1, and K_eq = (8 ± 4) × 10⁴ L mol^?1 for BMPT. The K_eq values are in satisfactory agreement with data from ab initio calculations.

     

Evaluation of renal oxygenation change under the influence of carbogen breathing using a dynamic R2, R2′ and R2* quantification approach

The purpose of this study is to demonstrate the feasibility of dynamic renal R₂/R₂′/R₂* measurements based on a method, denoted psMASE‐ME, in which a periodic 180° pulse‐shifting multi‐echo asymmetric spin echo (psMASE) sequence, combined with a moving estimation (ME) strategy, is adopted. Following approval by the institutional animal care and use committee, a block design of respiratory challenge with interleaved air and carbogen (97% O₂, 3% CO₂) breathing was employed in nine rabbits. Parametrical R₂/R₂′/R₂* maps were computed and average R₂/R₂′/R₂* values were measured in regions of interest in the renal medulla and cortex. Bland–Altman plots showed good agreement between the proposed method and reference standards of multi‐echo spin echo and multi‐echo gradient echo sequences. Renal R₂, R₂′ and R₂* decreased significantly from 16.2 ± 4.4 s^?1, 9.8 ± 5.2 s^?1 and 25.9 ± 5.0 s^?1 to 14.9 ± 4.4 s^?1 (p < 0.05), 8.5 ± 4.1 s^?1 (p < 0.05) and 23.4 ± 4.8 s^?1 (p < 0.05) in the cortex when switching the gas mixture from room air to carbogen. In the renal medulla, R₂, R₂′ and R₂* also decreased significantly from 12.9 ± 4.7 s^?1, 15.1 ± 5.8 s^?1 and 27.9 ± 5.3 s^?1 to 11.8 ± 4.5 s^?1 (p < 0.05), 14.2 ± 4.2 s^?1 (p < 0.05) and 25.8 ± 5.1 s^?1 (p < 0.05). No statistically significant differences in relative R₂, R₂′ and R₂* changes were observed between the cortex and medulla (p = 0.72 for R₂, p = 0.39 for R₂′ and p = 0.61 for R₂*). The psMASE‐ME method for dynamic renal R₂/R₂′/R₂* measurements, together with the respiratory challenge, has potential use in the evaluation of renal oxygenation in many renal diseases     

Evidence of break-points in breathing pattern at the gas-exchange thresholds during incremental cycling in young, healthy subjects

The present study investigated whether ‘break-points’ in breathing pattern correspond to the first ( G_\textEX1 G_{{{\text{EX}}_{1} }} ) and second gas-exchange thresholds ( G_{\textEX 2} G_{{{\text{EX}}_{ 2} }} ) during incremental cycling. We used polynomial spline smoothing to detect accelerations and decelerations in pulmonary gas-exchange data, which provided an objective means of ‘break-point’ detection without assumption of the number and shape of said ‘break-points’. Twenty-eight recreational cyclists completed the study, with five individuals excluded from analyses due to low signal-to-noise ratios and/or high risk of ‘pseudo-threshold’ detection. In the remaining participants (n = 23), two separate and distinct accelerations in respiratory frequency (f _R) during incremental work were observed, both of which demonstrated trivial biases and reasonably small ±95% limits of agreement (LOA) for the G_\textEX1 G_{{{\text{EX}}_{1} }} (0.2 ± 3.0 ml O₂ kg⁻¹ min⁻¹) and G_{\textEX 2} G_{{{\text{EX}}_{ 2} }} (0.0 ± 2.4 ml O₂ kg⁻¹ min⁻¹), respectively. A plateau in tidal volume (V _T) data near the G_\textEX1 G_{{{\text{EX}}_{1} }} was identified in only 14 individuals, and yielded the most unsatisfactory mean bias ±LOA of all comparisons made (−0.4 ± 5.3 ml O₂ kg⁻¹ min⁻¹). Conversely, 18 individuals displayed V _T-plateau in close proximity to the G_{\textEX 2} G_{{{\text{EX}}_{ 2} }} evidenced by a mean bias ± LOA of 0.1 ± 3.1 ml O₂ kg⁻¹ min⁻¹. Our findings suggest that both accelerations in f _R correspond to the gas-exchange thresholds, and a plateau (or decline) in V _T at the G_{\textEX 2} G_{{{\text{EX}}_{ 2} }} is a common (but not universal) feature of the breathing pattern response to incremental cycling.     

An increase in [Ca2+]i activates basolateral chloride channels and inhibits apical sodium channels in frog skin epithelium

 The aim of this study was to investigate the mechanisms by which increases in free cytosolic calcium ([Ca²⁺]_i) cause a decrease in macroscopic sodium absorption across principal cells of the frog skin epithelium. [Ca²⁺]_i was measured with fura-2 in an epifluorescence microscope set-up, sodium absorption was measured by the voltage-clamp technique and cellular potential was measured using microelectrodes. The endoplasmic reticulum calcium-ATPase inhibitor thapsigargin (0.4 μM) increased [Ca²⁺]_i from 66 ± 9 to 137 ± 19 nM (n = 13, P = 0.002). Thapsigargin caused the amiloride-sensitive short circuit current (I _sc) to drop from 26.4 to 10.6 μA cm^–2 (n = 19, P<0.001) concomitant with a depolarization of the cells from –79 ± 1 to –31 ± 2 mV (n = 18, P<0.001). Apical sodium permeability (P ^a _Na) was estimated from the current/voltage (I/V) relationship between amiloride-sensitive current and the potential across the apical membrane. P ^a _Na decreased from 8.01·10^–7 to 3.74·10^–7 cm s^–1 (n = 7, P = 0.04) following an increase in [Ca²⁺]_i. A decrease in apical sodium permeability per se would tend to decrease I _sc and result in a hyperpolarization of the cell potential and not, as observed, a depolarization. Serosal addition of the chloride channel inhibitors 4,4′-diisothiocyanatostilbene-2,2′-disulphonic acid (DIDS), diphenylamine-2-carboxylate (DPC), indanyloxyacetic acid 94 (IAA-94) and furosemide reversed the depolarization induced by thapsigargin, indicating that chloride channels were activated by the increase in [Ca²⁺]_i. This was confirmed in wash-out experiments with ³⁶Cl where it was shown that thapsigargin increased the efflux of chloride from 32.49 ± 5.01 to 62.63 ± 13.3 nmol·min^–1 cm^–2 (n = 5, P = 0.04). We conclude that a small increase in [Ca²⁺]_i activates a chloride permeability and inhibits the apical sodium permeability. The activation of chloride channels and the closure of apical sodium channels will tend to lower the macroscopic sodium absorption. Received: 25 June 1996 / Received after revision: 28 August 1996 / Accepted: 2 September 1996     

Effects of K-201 on the calcium pump and calcium release channel of rat skeletal muscle

The benzothiazepine derivative K-201 has been suggested as a potential therapeutic agent due to its antiarrhythmogenic action. To understand how the drug alters calcium release from the sarcoplasmic reticulum (SR), we investigated its effects on the SR calcium channel and calcium pump by single channel electrophysiology, whole-cell confocal microscopy, and ATPase activity measurements on control and post-myocardial infarcted (PMI) rat skeletal muscle. In bilayers, K-201 induced two subconductance states corresponding to ∼24% (S₁) and ∼13% (S₂) of the maximum conductance. Dependence of event frequency and of time spent in S₁ and S₂ on the drug concentration was biphasic both in control and in PMI rats, with a maximum at 50 μM. At this concentration, the channel spends 26 ± 4% and 24 ± 4%, respectively, of the total time in these subconductance states at positive potentials, while no subconductances are observed at negative potentials. K-201 altered the frequency of elementary calcium release events: spark frequency decreased from 0.039 ± 0.001 to 0.023 ± 0.001 s⁻¹ sarcomere⁻¹, while the frequency of embers increased from 0.011 ± 0.001 to 0.023 ± 0.001 s⁻¹ sarcomere⁻¹. Embers with different amplitude levels were observed after the addition of the drug. K-201 inhibited the Ca²⁺ ATPase characterized by IC_50,contr = 119 ± 21 μM and n _Hill,contr = 1.84 ± 0.48 for control and IC_50,PMI = 122 ± 18 μM and n _Hill,PMI = 1.97 ± 0.24 for PMI animals. These results suggest that although K-201 would increase the appearance of subconductance states, the overall calcium release is reduced by the drug. In addition, the effect of K-201 is identical on calcium release channels from control and PMI rats.     

Remodelling of the retinal arterioles in descending optic atrophy follows the principle of minimum work

Mathematical modelling indicates that the minimum energy cost for blood flow is achieved when the arteries are arranged in a branching hierarchy such that the radii of the vessels are adjusted to the cube root of the volumetric flow (principle of minimum work). This is known to apply over several magnitudes of vessel calibres, and in many different organs, including the brain, in humans and in animals. This paper addresses the issue of remodelling of one and the same arterial network to long-term changes in blood flow. This has not been studied previously in humans. We measured the radius of parent (r₀) and branch segments (r_l and r₂) of the retinal arteriolar network in fundus photographs of six patients with blinding, non-vascular retrobulbar optic nerve lesions, mostly traumatic in origin, before and after the development of descending optic atrophy. Attenuation of retinal arterioles is a well-known phenomenon in descending optic atrophy, and is attributable to decreased metabolic demand secondary to loss of the retinal ganglion cells and their axons. On average, arteriolar diameters decreased by 15.2±17.7% (SD), with 95% confidence intervals of 18.7% and 11.7%; the radii decreased significantly (P= 0.0001) (n= 99). The area ratio of the bifurcations, defined as (r²₁+r²₂)r^-₀², was 1.23±0.2 before, and 1.18±0.2 after optic atrophy (n= 36); the change of area ratio was not significant. The branching geometry of the retinal arteriolar network obeyed strictly the optimum branching rule of the principle of minimum work, or r³₀=r³₁+r³₂. Bifurcation exponents corrected for the Fåhræus-Lindquist effect were ?? 3 before optic atrophy and remained unchanged after remodelling of the arterioles. It is concluded that the branching of the retinal arterioles and their adaptation to long-term changes in blood flow in descending optic atrophy obey the principle of minimum work.     

Oral pre‐treatment with rosuvastatin protects porcine myocardium from ischaemia/reperfusion injury via a mechanism related to nitric oxide but not to serum cholesterol level

Aims: The aim of this study was to test whether oral pre‐treatment with rosuvastatin at a dosage giving clinically relevant plasma concentrations protects the myocardium against ischaemia/reperfusion injury and to investigate the involvement of nitric oxide (NO) and neutrophil infiltration. Methods: Pigs were given placebo (n = 7), rosuvastatin (80 mg day^?1, n =7), rosuvastatin (160 mg day^?1, n = 7) or pravastatin (160 mg day^?1, n = 7) orally for 5 days before being subjected to coronary artery ligation and reperfusion. An additional group was given rosuvastatin 160 mg day^?1 and a nitric oxide synthase (NOS) inhibitor. Results: Rosuvastatin 80 and 160 mg day^?1 resulted in plasma concentrations of 2.6 ± 0.7 and 5.6 ± 1.0 ng mL^?1, respectively. Serum cholesterol was not affected. Rosuvastatin 160 mg day^?1 and pravastatin limited the infarct size from 82 ± 3% of the area at risk in the placebo group to 61 ± 3% (P < 0.05), and to 61 ± 2% (P < 0.05) respectively. Rosuvastatin 80 mg day^?1 limited the infarct size to 69 ± 2%, however, this effect was not statistically significant. Rosuvastatin 160 mg day^?1 attenuated neutrophil infiltration in the ischaemic/reperfused myocardium. The protective effect of rosuvastatin 160 mg day^?1 was abolished by NOS inhibition. The expression of NOS2 and NOS3 in the myocardium did not differ between the groups. Conclusions: Oral pre‐treatment with rosuvastatin limited infarct size following ischaemia/reperfusion without affecting cholesterol levels. The cardioprotective effect is suggested to be dependent on maintained bioactivity of NO, without influencing NOS expression.     

Comparison of Na+-Ca2+ exchange current elicited from isolated rabbit ventricular myocytes by voltage ramp and step protocols

 In this study, the effects of three different voltage protocols on the Na⁺-Ca²⁺ exchange current (I _Na-Ca) of rabbit right ventricular myocytes were studied. Whole-cell patch-clamp recordings were made using a Cs⁺-based internal dialysis solution and external solutions designed to block major interfering currents. I _Na-Ca was measured at 35–37°C as (5 mM) Ni-sensitive current elicited by: a 2 s descending ramp (DR: +80 to –120 mV); a 2 s ascending ramp (AR: –120 to +80 mV) and 500 ms voltage steps (VS) between –120 and +80 mV. DR and AR were applied from –40 mV and elicited I _Na-Ca with reversal potentials (E _rev) of –17.6±2.5 mV (mean±SEM; n=16) and –46.2±4.1 mV (n=10; P=0.0001) respectively. This difference was maintained when the holding potential was –80 mV (–44.0±2.1 mV, n=24 and –86.3±4.8 mV, n=10; P=0.0001), when the internal Ca chelator (EGTA) was replaced with BAPTA (–19.5±1.8 mV and –46.3±1.6 mV, n=6; P=0.0003) and when DR and AR were applied alternately to the same cell. Experiments using modified ramp waveforms suggested a possible mechanism for these differences. Increases in subsarcolemmal Ca caused by Ca entry (coupled to Na extrusion) during the initial positive potential phase of the DR might have induced I _Na-Ca reversal at less negative potentials than observed with AR, during the initial phase of which subsarcolemmal Ca would not have accumulated. These data suggest that I _Na-Ca during voltage-clamp experiments can be significantly influenced by the type of voltage protocol chosen, as the protocol appears to induce subsarcolemmal changes in Ca and Na concentration that are independent of Ca buffering in the bulk cytosol and can occur on a pulse-to-pulse basis. Received: 23 October 1998 / Received after revision: 8 January 1999 / Accepted: 11 January 1999     

Water permeability of the mammalian cochlea: functional features of an aquaporin-facilitated water shunt at the perilymph–endolymph barrier

The cochlear duct epithelium (CDE) constitutes a tight barrier that effectively separates the inner ear fluids, endolymph and perilymph, thereby maintaining distinct ionic and osmotic gradients that are essential for auditory function. However, in vivo experiments have demonstrated that the CDE allows for rapid water exchange between fluid compartments. The molecular mechanism governing water permeation across the CDE remains elusive. We computationally determined the diffusional (P _D) and osmotic (P _f) water permeability coefficients for the mammalian CDE based on in silico simulations of cochlear water dynamics integrating previously derived in vivo experimental data on fluid flow with expression sites of molecular water channels (aquaporins, AQPs). The P _D of the entire CDE (P _D?=?8.18?×?10^?5 cm s^?1) and its individual partitions including Reissner's membrane (P _D?=?12.06?×?10^?5 cm s^?1) and the organ of Corti (P _D?=?10.2?×?10^?5 cm s^?1) were similar to other epithelia with AQP-facilitated water permeation. The P _f of the CDE (P _f?=?6.15?×?10^?4 cm s^?1) was also in the range of other epithelia while an exceptionally high P _f was determined for an epithelial subdomain of outer sulcus cells in the cochlear apex co-expressing AQP4 and AQP5 (OSCs; P _f?=?156.90?×?10^?3 cm s^?1). The P _f/P _D ratios of the CDE (P _f/P _D?=?7.52) and OSCs (P _f/P _D?=?242.02) indicate an aqueous pore-facilitated water exchange and reveal a high-transfer region or “water shunt” in the cochlear apex. This “water shunt” explains experimentally determined phenomena of endolymphatic longitudinal flow towards the cochlear apex. The water permeability coefficients of the CDE emphasise the physiological and pathophysiological relevance of water dynamics in the cochlea in particular for endolymphatic hydrops and Ménière's disease.     

Bestimmung der geschwindigkeitskonstanten und der effektivitäten beim zerfall von 2,2′-azoisobutyronitril in styrol,N-vinyl-2-pyrrolidon und methylmethacrylat

The decomposition rate constants k_d of initiators can be determined by a new method directly in monomers as solvents. If a suitable inhibitor is added to a monomer mixture with the initiator the latter decomposes nearly without monomer conversion. The initiator concentration—after the inhibitor is consumed—can be found by means of the dilatometrically determined polymerization rate after the induction period. The functional connection between polymerization rate and initiator concentration found without inhibitor is used as a calibration curve for that purpose. The dilatometrical measurements were made in the monomers styrene and N-vinyl-2-pyrrolidone using 2,2′-azoisobutyronitrile (AIBN) as initiator and p-quinone as inhibitor. The following decomposition rate constants were found: k_d=1,52 · 10^?5 S^?1 (styrene) and k_d=1,62 · 10^?5 S^?1 (N-vinyl-2-pyrrolidone), which is in agreement with literature values. Initiator efficiencies f were calculated: f=0,46 (styrene), f=0,47 (N-vinyl-2-pyrrolidone). In methyl methacrylate (MMA) 2,2′-diphenyl-1-picrylhydrazyl (DPPH) was used as inhibitor. Under certain conditions the product k_df can be calculated from the consumption rate of DPPH. The value found in MMA (k_df=3,7 · 10^?6 s^?1) is lower than that reported in literature (6,45 · 10^?6 s^?1).     

Separation of early afterdepolarizations from arrhythmogenic substrate in the isolated perfused hypokalaemic murine heart through modifiers of calcium homeostasis

Aims: We resolved roles for early afterdepolarizations (EADs) and transmural gradients of repolarization in arrhythmogenesis in Langendorff‐perfused hypokalaemic murine hearts paced from the right ventricular epicardium. Methods: Left ventricular epicardial and endocardial monophasic action potentials (MAPs) and arrhythmogenic tendency were compared in the presence and absence of the L‐type Ca²⁺ channel blocker nifedipine (10 nm –1 μm ) and the calmodulin kinase type II inhibitor KN‐93 (2 μm ). Results: All the hypokalaemic hearts studied showed prolonged epicardial and endocardial MAPs, decreased epicardial‐endocardial APD₉₀ difference, EADs, triggered beats and ventricular tachycardia (VT) (n = 6). In all spontaneously beating hearts, 100 (but not 10) nm nifedipine reduced both the incidence of EADs and triggered beats from 66.9 ± 15.7% to 28.3 ± 8.7% and episodes of VT from 10.8 ± 6.3% to 1.2 ± 0.7% of MAPs (n = 6 hearts, P < 0.05); 1 μm nifedipine abolished all these phenomena (n = 6). In contrast programmed electrical stimulation (PES) still triggered VT in six of six hearts with 0, 10 and 100 nm but not 1 μm nifedipine. 1 μm nifedipine selectively reduced epicardial (from 66.1 ± 3.4 to 46.2 ± 2.5 ms) but not endocardial APD₉₀, thereby restoring ΔAPD₉₀ from ?5.9 ± 2.5 to 15.5 ± 3.2 ms, close to normokalaemic values. KN‐93 similarly reduced EADs, triggered beats and VT in spontaneously beating hearts to 29.6 ± 8.9% and 1.7 ± 1.1% respectively (n = 6) yet permitted PES‐induced VT (n = 6), in the presence of a persistently negative ΔAPD₉₀. Conclusions: These findings empirically implicate both EADs and triggered beats alongside arrhythmogenic substrate of ΔAPD₉₀ in VT pathogenesis at the whole heart level.