The effectiveness of the control of pH in the extracellular fluid of the brain by the respiratory control system

Summary The effectiveness of the respiratory control system as a regulator of the pH in the extracellular fluid of the brain is defined by pH_{ECF op}/pH_{ECF cl} where pH_{ECF op} means the primary or open loop shift and pH_{ECF cl} the final or closed loop shift of brain extracellular fluid pH. The analysis of a steady state model described in a preceding paper (Loeschcke, 1973) allows, in the limits of the suppositions and simplifications, to calculate the effectiveness of the feedback regulator in the cases of increased metabolism, metabolic acidosis-alkalosis and inhalation of CO₂. The effectiveness is diminished if CO₂ production is increased, it drops in metabolic acidosis and rises in metabolic alkalosis and it drops steeply if CO₂ is inhaled. The effectiveness of this control system depends on the controlling action of the controlling element (the ventilation) rather than on varying sensitivity of the sensing element. The controlling effect is defined asC=–d P _CO2/d V _A orC=d pH_ECF/d V _A.Im Rahmen des Programms des Sonderforschungsbereiches 114 (Bionach) der Deutschen Forschungsgemeinschaft.     

Relationship between muscle architectural features and oxygenation status determined by near infrared device

This study tested whether regional differences in oxygenation status could result from differences in muscle fiber architecture. Architectural properties, oxygen supply, and consumption in the medial head of the gastrocnemius muscle (GM) were determined in vivo in six men using B-mode ultrasound and functional near infrared (NIR) imaging devices. Fascicle length, fascicle angle, NIR-O₂ saturation (deoxygenated Hb or oxygenated Hb), and NIR-blood volume (sum of deoxygenated and oxygenated Hb) were obtained in the distal and proximal portions of the GM at rest and during contraction. Exercise consisted of 2 min of standing plantar flexion at 1 Hz with an additional load of 50% of each subjects weight. Plantar flexion produced larger decreases (: difference between rest and exercise values) in NIR-O₂ saturation [mean saturation (SD) of 0.14 (0.05) vs 0.07 (0.04) optical density units] and NIR-blood volume [mean saturation (SD) of –0.23 (0.08) vs –0.13 (0.04) optical density units] in the distal compared with the proximal portion (P<0.05 for all comparisons). It also produced larger changes () in fascicle length [mean length (SD) of –16.5 (4.7) vs –8.2 (4.2) mm] and fascicle angle (mean angle (SD) of 10.8 (1.4)° vs 3.9 (2.1)°] in the distal compared with the proximal portion (P<0.05 for all comparisons). There were significant correlations between NIR-O₂ saturation and fascicle length (r=–0.84, P<0.05), and between NIR-O₂ saturation and fascicle angle (r=–0.90, P<0.05), between NIR-blood volume and fascicle length (r=0.91, P<0.05), between NIR-blood volume and fascicle angle (r=–0.85, P<0.05). In conclusion, the plantar flexion exercise produced regional differences in oxygenation status consistent with regional differences in muscle architecture.     

Effects of priming exercise intensity on the dynamic linearity of the pulmonary V̇O2 response during heavy exercise

Prior heavy-intensity exercise facilitates the pulmonary oxygen uptake (O₂) response during subsequent exercise, such that its kinetics returns towards first-order. To better understand this priming phenomenon, we investigated the effect of priming exercise, over a range of intensities, on the O₂ response to heavy-intensity cycle ergometry at a work rate of 50% [halfway between lactate threshold (LT) and O_2max]. Eight subjects performed two consecutive 6-min bouts separated by 6 min at 20 W. The first bout was each of: no warm-up control (CON), sub-lactate threshold (LT) at 80% of LT, and three supra-LT conditions (20%, 40%, and 60%). The O₂ response during the subsequent bout was evaluated using the effective time constant (), and the O₂ difference between minutes 3 and 6 (O_2(6–3)). The goodness-of-fit, indicative of first-order kinetics, was determined by the residual profile, and the mean square of errors (MSEr). The heart rate and blood lactate concentration ([La]r) just prior to the second bout were also measured. Compared with CON, and O_2(6–3) were significantly reduced following all supra-LT priming bouts, while the goodness-of-fit was significantly improved following 40% exercise. O_2(6–3) and [La]r were negatively correlated (P<0.05), unlike HR. In conclusion, prior exercise just above, but not below, LT facilitated the O₂ response in a threshold-like manner. Supra-LT priming exercise influenced the O₂ response allowing it to return to within as little as 12% from first-order (compared to ~50% in CON). The associated increases in circulating lactate and/or related factors seem to be centrally involved in this phenomenon.     

Einfluß von Aldosteron auf den Natriumtransport in den Sammelrohren der Säugetierniere

Zusammenfassung Durch Mikropunktion und -perfusion der Vasa recta an der freigelegten Nierenpapille von Wistarratten wurde es möglich, die schwankenden Harnstoff- und Natriumkonzentrationen im Interstitium des Nierenmarks zu beseitigen und definierte Versuchsbedingungen für die Sammelrohre zu schaffen.An diesen funktionell isolierten Sammelrohrabschnitten wurdenin situ sowohl die Gleichgewichtskonzentrationsdifferenz bei fehlendem Nettosubstanz-und -volumenfluß (C _Na) als auch der Nettonatriumtransport ( _Na) bei gleicher Natriumkonzentration auf beiden Seiten der Sammelrohrwand gemessen. Es konnte gezeigt werden, daß unter diesen Versuchsbedingungen, bei denen die Tiere in Antidiurese sind, die Natriumrückresorption aus den Sammelrohren isoton abläuft.Die Versuche wurden an vier Tiergruppen durchgeführt: an adrenalektomierten Tieren, an normal ernährten Tieren, an salzarm ernährten Tieren und an normal ernährten Tieren, die zusätzlich Aldosteron bekamen. _{Na iso} war bei adrenalektomierten Tieren 1,2·10^–5 bei normal ernährten Tieren 3,1·10^–5, bei salzarm ernährten Tieren 4,1·10^–5 und bei normal ernährten Tieren unter Aldosteronsubstitution 4,2·10^–5 Äq·mm^–2·sec^–1. Die entsprechenden C _Na werte waren 4, 31, 98, 93 mÄq/l.Unter der Annahme, daß _{Na iso} die Transportkapazität des Systems angibt und daß C _Na bei gegebenem _{Na iso} umgekehrt proportional der Leckpermeabilität für Natriumionen ist, kann man aus den vorliegenden Daten schließen, daß Aldosteron am Sammelrohr nicht nur die innere Transportkapazität für Na erhöht, sondern auch die Leckpermeabilität für Na herabsetzt.     

Time-dependent effect of sectioning carotid sinus nerves on the vagally mediated baroreflex

The purpose of the reported experiments was to examine whether the vagally mediated baroreflex system (V-system) increases its feedback gain with time after sectioning of the carotid sinus nerves (CSN). In 10 dogs anesthetized with Nembutal, we determined the overall open-loop gain (G) of the rapidly acting arterial pressure control system. G was assessed as (AP_I/AP_S)-1, where AP_I and AP_S represent the immediate and steady-state decreases in arterial pressure at the aortic arch following a fast step-wise reduction in blood volume. AP_I, AP_S and G_INTACT in the intact condition (30th min before sectioning of the CSN) were –1.8±0.1 kPa, –0.20±0.01 kPa and 8.4±0.3 (mean±SE), respectively. The mean values of AP_I, AP_S and G after sectioning of the CSN (G_V), first averaged within individual dogs and then averaged for ten dogs, were –2.53±0.07 kPa, –1.1±0.05 kPa, and 1.5±0.1, respectively. G_V did not change with time over about 4 h after sectioning of the CSN. It is concluded that the V-system cannot augment its ability to restore arterial pressure in compensation for the lost function of the carotid sinus baroreflex system over 4 h after sectioning of the CSN in the anesthetized dog.     

Natriumtransport in den proximalen Tubuli und den Sammelrohren bei Variation der Natriumkonzentration im umgebenden Intterstitium

Zusammenfassung An Ratten wurden Mikropunktionsuntersuchungen am proximalen Tubulus und am Sammelrohr bei Durchblutung der peritubulären Capillaren bzw. Vasa recta sowie bei künstlicher Perfusion dieser Blutgefäße durchgeführt. In Abhängigkeit von der Höhe der interstitiellen Natriumkonzentration wurden der Nettonatriumtransport (_{Na iso}) bei gleicher Natriumkonzentration zu beiden Seiten der Tubuluswand und die Gleichgewichtskonzentrationsdifferenz (c _Na) bei fehlendem Nettovolumen- und Nettosubstanzfluß gemessen.Bei Variation der Natriumkonzentration im Gewebe durch Perfusion der peritubulären Capillaren mit 155 bzw. 300 mÄq/l Na änderten sich weder _{Na iso} noch c _Na für den proximalen Tubulus (_{Na iso} 8,4 bzw. 7,9·10^–5 Äq · mm^–2 · sec^–1; c _Na 24 bzw. 24 mÄq/l). Veränderung der Natriumkonzentration im Blut durch Infusion hypertoner NaCl Lösung oder Peritonealdialyse mit isotoner Mannitlösung führten zu prinzipiell gleichen Ergebnissen. Bei Perfusion der Vasa recta mit Lösungen, die 145 und 300 mÄq/l Natrium entheilten, blieben _{Na iso} wie c _Na über die Sammelrohrwand ebenfalls konstant (_{Na iso} 4,1 bzw. 4,1·10^–5 Äq · mm^–2 · sec^–1; c _Na 98 bzw. 104 mÄq/l). Proximale Tubuli und Sammelrohre verhalten sich demnach bei Variation der interstitiellen Natriumkonzentration gleich.Da die Wasserresorption aus den Sammelrohren von dem durch Gegenstrommultiplikation erzeugten Natriumkonzentrationsanstieg im Markinterstitium abhängt, die Natriumresorption aus den Sammelrohren aber wie die vorliegenden Befunde zeigen von eben dieser Natriumkonzentration unabhängig ist, ist dem Warmblüterorganismus die Möglichkeit gegeben, Natrium- und Wasserresorption unabhängig voneinander zu variieren. Die Natrium- und Wasserresorption aus den Sammelrohren werden jedoch beide durch den Gehalt der Sammelrohrflüssigkeit an permeablen Nichtelektrolyten, wie z. B. Harnstoff, beeinflußt.Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.     

Cupula displacement,hair bundle deflection,and physiological responses in the transparent semicircular canal of young eel

The transparent labyrinth of young eels (Anguilla anguilla L.) was used in toto for studying the configuration of cupula displacement, deflection of the hair bundle, and correlated changes in transepithelial voltage (TEV) and nerve activity (NA) in the semicircular canal. Microcapillaries were introduced into the canal through holes produced by a microthermocauter. Mechanical stimulation was applied either by injection of fluid into the ampulla or by electromagnetically displacing ferrofluid as a piston within the canal. Motion of individual kinocilia, stained cupulae or the ferrofluid piston was analysed by double-exposed microphotographs, photodiodes, or a video-system. The three-dimensional cupula displacement configuration was found to be piston-to diaphragm-like. Hair bundles at different sites on the crista exhibit differences in amplitude and time course of deflection. The transfer factor between shifts of the canal fluid and the tips of the kinocilia is 0.4–0.6. Displacements in opposite directions induce TEV and NA of opposite sign. Various tests confirmed TEV to reflect receptor potential responses. Nerve activity adapts to a tonic response with a time constant of 6.4s. No similar adaptation occurred in TEV. Stimulus-response curves of TEV- and NA-responses are similar and signoid in shape with saturation at ciliary deflections of roughly + 6° and –3°.     

Overshoot in <Emphasis Type="Italic">V̇</Emphasis>O<Subscript>2</Subscript> following the onset of moderate-intensity cycle exercise in trained cyclists

We have previously observed that following the onset of moderate intensity cycle ergometry, the pulmonary O₂ uptake (O₂) in trained cyclists often does not increase towards its steady-state value with the typical mono-exponential characteristics; rather, there is a transient overshoot. The purpose of this study was to systematically examine this phenomenon by comparing the O₂responses to two moderate-intensity work rates and one high-intensity work rate in trained and untrained subjects. Following a ramp exercise test to the limit of tolerance for the determination of the gas exchange threshold (GET) and O_2peak, seven trained cyclists [mean (SD); O_2peak 66.6 (2.5) ml·kg^–1·min^–1] and eight sedentary subjects [O_2peak 42.9 (5.1) ml·kg^–1·min^–1] completed six step transitions from baseline cycling to work rates requiring 60% and 80% GET and three step transitions from baseline cycling to a work rate requiring 50% of the difference between GET and O_2peak (50%). O₂ was measured breath-by-breath and modelled using standard techniques. The sedentary subjects did not overshoot the steady-state O₂ at any intensity. At 60% GET, six of the seven cyclists overshot the steady-state O₂ [by an integral volume of 164 (44) ml between ~45 and 125 s]. At 80% GET, four of the seven cyclists overshot the steady-state O₂ [by an integral volume of 185 (92) ml between ~55 and 140 s]. None of the cyclists showed an overshoot at 50%. These results indicate that trained cyclists evidence an overshoot in O₂ before steady-state is reached in the transition to moderate-intensity exercise. The mechanism(s) responsible for this effect remains to be elucidated, as does whether the overshoot confers any functional or performance benefit to the trained cyclist.     

Structural and functional mitochondrial abnormalities associated with high levels of partially deleted mitochondrial DNAs in somatic cell hybrids

Kearns-Sayre syndrome (KSS) is a progressive and ultimately fatal human encephalomyopathy that is associated with large-scale deletions of mitochondrial DNA (mtDNA). To gain new insights into the developmental pathobiology of this disease, we studied the maintenance and expression of deleted mtDNAs (-mtDNAs) in somatic cell hybrids generated by fusion of HeLacot cells with a KSS fibroblast clone containing both wild-type and -mtDNAs. We observed that -mtDNAs were preferentially maintained over the KSS wild-type mtDNAs (wt-mtDNAs) in almost all isolated hybrid clones. Mitochondrial metabolism was not compromised in hybrids containing as much as 70–79% -mtDNAs. Two clones containing more than 99% -mtDNA were severely deficient in oxidative phosphorylation and exhibited abnormal, enlarged mitochondria. These clones had undetectable levels of mtDNA-encoded polypeptides, but contained normal amounts of a nuclear DNA-encoded mitochondrial protein. The data suggest a nonrandom pattern of mtDNA segregation in the triplasmic hybrids and a correlation among -mtDNA, structural mitochondrial abnormalities, and mitochondrial dysfunction.     

Influence of muscle fibre type and pedal rate on the V̇O2-work rate slope during ramp exercise

We hypothesised that the ratio between the increase in oxygen uptake and the increase in work rate (O₂/WR) during ramp cycle exercise would be significantly related to the percentage type II muscle fibres at work rates above the gas exchange threshold (GET) where type II fibres are presumed to be active. We further hypothesised that ramp exercise at higher pedal rates, which would be expected to increase the proportional contribution of type II fibres to the total power delivered, would increase the O₂/WR slope at work rates above the GET. Fourteen healthy subjects [four female; mean (SD): age 25 (3) years, body mass 74.3 (15.1) kg] performed a ramp exercise test to exhaustion (25 W min^–1) at a pedal rate of 75 rev min^–1, and consented to a muscle biopsy of the vastus lateralis. Eleven of the subjects also performed two further ramp tests at pedal rates of 35 and 115 rev min^–1. The O₂/WR slope for exercise <GET (S ₁) was significantly correlated with O₂ peak in ml kg^–1 min^–1 (r=0.60; P<0.05), whereas the O₂/WR slope for exercise >GET (S ₂) was significantly correlated to percentage type II fibres (r=0.54; P=0.05). The ratio between the O₂/WR slopes for exercise above and below the GET (S ₂/S ₁) was significantly greater at the pedal rate of 115 rev min^–1 [1.22 (0.09)] compared to pedal rates of 35 rev min^–1 [0.96 (0.02)] and 75 rev min^–1 [1.09 (0.05), (P<0.05)]. The greater increase in S ₂ relative to S ₁ in subjects (1) with a high percentage type II fibres, and (2) at a high pedal rate, suggests that a greater recruitment of type II fibres contributes in some manner to the xs O₂ observed during ramp exercise.     

Volume flow,hydraulic conductivity and electrical properties across bovine tracheal epithelium in vitro: Effect of histamine

Volume flow (J _v), potential difference (), shortcircuit current (i ₀) and electrical resistance (R) were measured simultaneously across bovine tracheal epithelium in vitro. Under basal conditions, with no applied hydrostatic or osmotic pressure gradient (P=0, =0), no spontaneousJ _v was observed. was 31±2 mV (lumen negative),i ₀ 161±8 A cm^–2 andR 202±9 cm²,n=50. When a was applied, by adding 20–80 mM sucrose into the medium bathing either the luminal or the serosal side of the tissue, a linear relationship was found between andJ _v toward the lumen or toward the serosa. The apparent hydraulic conductivity (apparentL _p) was 4.6–4.910^–6 cm s^–1 atm^–1. Histamine 10^–4 M did not induce any spontaneousJ _v under basal conditions and had no effect oni ₀ nor onR. However, histamine caused a 100% increase inJ _v elicited by sucrose gradients. It was concluded that histamine exerts a selective action on the hydraulic conductivity of bovine tracheal epithelium. Experiments using H₁-receptors antagonists (diphenhydramine, dimetindene, chloropyramine) and H₂-antagonists (cimetidine, metiamide) or a H₂-agonist (impromidine) showed that the increase ofL _p induced by histamine was mediated via H₂-receptors.Supported by the Swiss National Foundation (SNF), grant no. 3.5880.79     

Heat storage and body temperature during cooling and rewarming

Summary During calorimetric experiments with forced cooling and rewarming, changes in rectal temperature (T _re) and mean skin temperature ( _sk) allowed calculations of Burton's (1935) weighting coefficient a, which relates body temperature change to change in mean body temperature ( _b). Calculating _b from change in body heat content (H _b), which was determined from direct and indirect calorimetry, included individualized values for body specific heat based on body fat content. In five different cooling procedures there were two with cooling by exposure to cold water and three with cooling in a tubing suit; two of the procedures included mild exercise. The H _b ranged from –335 to –1600 kJ; rewarming restored body heat content. The mean (SEM) value of a in 119 determinations was 0.75 (0.01). This small variability in the coefficient probably came from the large values of H _b and from the use of maximal changes in _sk andT _re, including afterdrop. Change inT _re by itself correlated with _b, but with much variability. In forced body cooling and rewarming, 0.75(T _re) + 0.25 ( _sk) gives an accurate estimate of _b, hence change in body heat storage.     

Indices for the role played by regional flow resistance in blood pressure reflex

Summary An index, = (r/r)/(R/R), is proposed for assessment of the relative degree of participation of a regional flow resistance in a blood pressure reflex, wherer andR are regional and total peripheral resistances respectively and 's refer to their reflexive changes. For actual computation, =I (iP – Pi)/i(IP – PI), whereI=cardiac output,i=regional flow rate,P=mean arterial pressure. When the change in cardiac output is neglegible, the above equation is simplified as =1 – Pi/iP. Another index, = g/G = (Pi – iP)/(PI – IP), is introduced for the degree of contribution of a region to a reflex, whereg andG are regional and total conductances.i = 1. Some examples of application of the indices are presented.Supported in part by a grant from the Ministry of Education of Japan.     

Amino acids 519–524 of Dictyostelium myosin II form a surface loop that aids actin binding by facilitating a conformational change

Residues 519–524 of Dictyostelium myosin II form a small surface loop on the actin binding face, and have been suggested to bind directly to actin through high affinity hydrophobic interactions. To test this hypothesis, we have characterized mutant myosins that lack this loop in vivo and in vitro. A mutant myosin in which this loop was replaced by an Ala residue (519–524/+A) was non-functional in vivo. Replacement with a single Gly residue instead of Ala yielded partial function, suggesting that structural flexibility, rather than hydrophobicity, is the key feature of the loop. The in vivo phenotype of the mutant enabled us to identify a number of additional amino acid changes that restore function to the 519–524/+A mutation. Intriguingly, many of these, including L596S, were located at some distances away from the 519–524 loop. We have also isolated suppressors for the L596S mutant myosin, which was not functional in vivo. The suppressors for 519–524/+A and those for L596S showed complementary charge patterns. In ATPase assays, 519–524/+A S1 showed very low activity and little enhancement by actin, whereas L596S S1 was hyper active and displayed enhanced affinity for actin. In motility assays, 519–524/+A myosin released actin filaments upon addition of ATP and was unable to support movements. L596S myosin was also inactive, but in this case actin filaments stayed immobile even after the addition of ATP. Transient kinetic measurements demonstrated that 519–524/+A S1 is not only slower than wild type to bind actin filaments, but also slower to dissociate from actin filaments. Based on these results, we concluded that the 519–524 loop is not a major actin binding site but aids actin binding by facilitating a critical conformational change.     

Serum carbonic anhydrase III,an enzyme of type I muscle fibres,and the intensity of physical exercise

The effects of 30 min running with stepwise increasing intensity (exhaustive, energy demand approx. 50 100% ofVO_2max), 60 s supramaximal running (anaerobic, 125% ofVO_2max) and 40–60 min low-intensity running (acrobic, 40–60% ofVO_2max) on serum concentration of muscle-derived proteins were studied in 5 male and 5 female elite orienteerers. S-Carbonic anhydrase III (S-CA III) was used as a marker of protein leakage from type I (slow oxidative) muscle fibres and S-myoglobin (S-Mb) as a non-selective (type I+II) muscular marker. The fractional increase in S-CA III (S-Ca III) was 0.37±0.09 (mean±SEM,p<0.001), 0.10±0.05 (N. S.) and 0.46±0.09 (p<0.001) 1 h after exhaustive, anaerobic and aerobic exercise, respectively. The corresponding values for S-Mb were 1.45±0.36 (p<0.001), 0.39±0.13 (p<0.01) and 0.67±0.18 (p<0.001). The value for the S-CA III/S-Mb ratio was 0.68±0.03 after the acrobic exercise, but only 0.25–0.26 (p vs. aerobic exercise <0.001) after the two high-intensity forms of exercise. Since type I fibres of skeletal muscle are known to be responsible for power production during low-intensity exercise, whereas fibres of both type I and type II are active at higher intensities, the S-CA III/S-Mb ratio may depend on the recruitment profile of type I vs. type I+II fibres.     

Trait anxiety,submaximal physical exercise and blood androgens

Summary This study evaluates the relationship between trait anxiety and both androgen and gonadotrophic hormone levels at rest and during severe physical exercise. Twelve volunteers were selected among 160 untrained male collegial students and classified as anxious (N=6) or non-anxious (N=6) subjects according to their scores on three trait-anxiety tests (STAI, IPAT, 16 PF). Serum ⁴-androgen (testosterone and ⁴-androstenedione), ⁴-androgen (DHEA and DHEA-SO₄) and gonadotrophin (LH and FSH) concentrations were measured by radioimmunoassay before, during and after 20 minutes of intensive bicycle exercise (80% of maximal heart rate). Results indicate significantly lower serum ⁴-androgens in anxious subjects before exercise. However, for each subject and irrespective of his anxiety level, all measured serum androgen concentrations increased significantly during exercise, although ⁴-androstene-dione remained lower in anxious subjects than in non-anxious ones. Serum LH concentrations (but not FSH) were signicantly higher in anxious subjects throughout the observation periods. However, exercise induced in each subject a significant decrease in the serum level of both gonadotrophic hormones. The results suggest that trait anxiety level may constitute an important factor that affects both pre-exercise and exercise serum androgen concentrations in untrained subjects.     

Comparison of the buffer capacity of endocytotic vesicles,lysosomes and cytoplasm in cells derived from the proximal tubule of the kidney (opossum kidney cells)

During transepithelial acid-base transport cells of the proximal tubule of the kidney have to maintain a relative constant intracellular pH. Herein cellular buffer capacity plays an important role. We measured vesicular buffer capacity in proximal tubule-derived opossum kidney cells and compared it with cytoplasmic buffer capacity to determine the possible importance of vesicular buffer capacity for cellular pH homeostasis. Under HCO₃ ^–-free conditions endocytotic vesicular buffer capacity was 43±4 mmol·l^–1·pH-unit^–1 (n=7) and exceeded cytoplasmic buffer capacity (19±3 mmol·l^–1 ·pH-unit^–1; n=7) significantly. Lysosomal buffer capacity was 19±6 mmol·l^–1·pH-unit^–1; (n=5). Inhibition of vesicular H⁺-ATPase using bafilomycin A₁ led to a dramatic increase of vesicular pH but to a decrease of cytoplasmic pH indicating the importance of organellar buffer systems. We estimated that endocytotic buffer capacity accounts for 23% of cellular buffer capacity under our experimental condition and thus, impairment of endosomal acidification may affect cytoplasmic pH indeed. From our results we conclude that endocytotic vesicles have a large buffer capacity and might play a role in cellular pH homeostasis.     

The continuous measurement of tubular volume changes in response to step changes in contraluminal osmolality

A new method to measure time dependent (t) volume (V) changes in proximal straight tubules (PST) is described.V is calculated from diameter (d) measurements for which a video camera and an integrating circuit are used. A tubular image of high optical contrast is recorded with the TV camera such that the scan lines run crosswise to the tubule. The video signal is analyzed by a special processor which adds 225 tubular diameters of each TV frame and feeds this analog signal to a pen recorder. The fractional error ind measurements is 10^–3. Diameter changes of less than 0.05 m can be detected, as compared to the usual error of a single measurement of about 0.4 m.P _os ^cb , the osmotic water permeability of the contraluminal cell membrane was measured by setting up osmotic steps across it in less than 0.1 s and following the ensuing d/t. the time delay between solution change and the linear part of the osmotic response was 0.51±0.05 s.P _os ^cb was found to be 50.4 (±8.7)×10^–4 cm³·cm^–2 of basement membrane area ·s^–1·osmolar^–1.     

Organization of assembly factors Cbp3p and Cbp4p and their effect on bc 1 complex assembly in Saccharomyces cerevisiae

The bc₁ complex (complex III) of Saccharomyces cerevisae is composed of ten subunits that are assembled in the inner mitochondrial membrane. Cbp3p and Cbp4p are two mitochondrial proteins which are postulated to act as chaperones in bc₁ complex formation. Here, we show by blue native PAGE that cbp3 and cbp4 mutants are disturbed in complex III assembly and accumulate intermediate-sized forms of the complex. Moreover, deletion of CBP3 interferes with the formation of complex III/IV supracomplexes. Our studies show that Cbp3p and Cbp4p interact and are present in high-molecular-weight complexes, some of which might represent intermediates of complex III assembly. Overexpression of Cbp4p cannot substitute for the function of Cbp3p, but high-level expression of Cbp3p can partially compensate for the lack of Cbp4p. The finding that mitochondria of cbp3 and cbp4 mutants exhibit a wild-type lipid composition favors the idea that Cbp3p and Cbp4p are specific assembly factors for complex III rather than components of the mitochondrial lipid metabolism.     

Lactate removal during active recovery related to the individual anaerobic and ventilatory thresholds in soccer players

The aim of this study was to compare the lactate (La) removal during active recovery at three different work rates below the individual anaerobic threshold (IAT). Recently, it has been recommended that exercise intensity should be determined in relation to the IAT instead of the percentage of maximal oxygen uptake (O_2max), especially for training and research purposes. Therefore, we defined the recovery work rates by calculating 50% of the threshold difference (T) between the IAT and the individual ventilatory threshold (IVT) work rates, then choosing the IVT_+50%T, the IVT and the IVT_–50%T. All these work rates fell within the range (30–70% O_2max) previously reported for optimal La removal. After a 6-min treadmill run at 90% O_2max, soccer players [n=12 male, age 22 (1) years] performed, in a random order, four 30-min recovery treatments: (1) run at IVT_+50%T, (2) at IVT, (3) at IVT_–50%T, (4) passive recovery. La was obtained at 1, 3, 6, 9, 12, 15, 20, 25 and 30 min of recovery. The La removal curve was significantly affected by treatments (P<0.01) and recovery timing (P<0.01), with a significant interaction between them (P<0.01). Although they were more efficient than passive recovery, the studied work rates [between 39 (7) and 60 (4)% O_2max) produced different lactate removal curves. IVT and IVT_–50%T were significantly more efficient than IVT_+50%T, while no difference was found between IVT and IVT_–50%T for any time point. In conclusion, both IVT_–50%T and IVT were efficient individual work rates for La removal, and no further La decrease occurred after 20 min.An erratum to this article can be found at