摘要:

In this review recent findings on the energetics offish larvae are presented, highlighting some of the physiological problems linked to small body size. The existence of a mass‐independent phase of specific metabolic rate is confirmed but it is pointed out that in young fish ontogenetic transitions of metabolic scaling have so far been documented only for the routine level of activity. Maximum metabolic rate is limited by mitochondrial density in the swimming muscles which scales with a mass exponent of ˜ 0.9. Mitochondrial density in the swimming muscles of a species of fish, from larva to adult, covers about the same range as mitochondrial density in the skeletal muscles of mammals. However, the aerobic capacity (power density) of mitochondria is one order of magnitude lower in fish than in mammals. Energy metabolism in embryos and early larvae of fish is almost entirely aerobic. Anaerobic power in the fast muscle fibres is low after hatching but increases during the transition from larva to Juvenile with a mass exponent greater than one. In hypoxic water fish larvae swim more economically (i.e. their cost of transport is lower) than in normoxic water. If the rate of growth exceeds a critical threshold (about 10% d‐1) fish larvae are capable of increasing the apparent efficiency of growth, probably by reducing the costs of other energy‐consuming functions of maint

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1995.tb09912.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

A hind limb of young adult, adult and old male Wistar rats (4–5, 6–7 and 20–21 months, respectively) was immobilized for 4 weeks by a plaster cast with the knee and ankle joints in a resting position. Enzyme‐histochemical, morphometrical and contractile characteristics of the soleus muscle were compared with those in age‐matched controls. A pronounced decrease in muscle mass and cross‐sectional muscle fibre area was found at all ages. The degree of atrophy after immobilization did not differ between different fibre types in each age group, but the decrease in fibre area was less pronounced in old animals (i.e. the fibre area was decreased by 49–64, 53–66 and 27–38% in young adult, adult and old animals, respectively). The maximum tetanus force was decreased in all age groups (by73,78 and 69% in young adult, adult and old rats, respectively) as was the tetanus tension (i.e. tetanus force divided by muscle fibre cross‐sectional area). The contraction time of the isometric twitch was significantly altered, i.e. decreased, only in the youngest age group, although it also tended to decrease in old age. A significant increase in the number and proportion of fibre types intermediate to types I and 11 A, was found in the immobilized muscle of 4–5‐ and 6–7‐month‐old animals, but not in that of old ones (i.e. the proportion of intermediate fibres increased by14,13 and 2% in young adult, adult and old animals, respectively). Thus, in contrast to the atrophic changes, the contractile alterations after immobilization were not markedly different between young and old age. It is further concluded that the age‐related fast‐to‐slow muscle fibre transition that occurs in normal soleus during maturation and growth can be partly reversed by restrictions of the normal muscle activity and that the ability of the soleus to modulate its fibre‐type composition in response to a change in

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1995.tb09913.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Seven male subjects performed repeated bouts of high‐intensity exercise, on a cycle ergometer, before and after 6 d of creatine supplementation (20 g Cr H2O day‐1). The exercise protocol consisted of five 6‐s exercise periods performed at a fixed exercise intensity, interspersed with 30‐s recovery periods (Part I), followed (40 s later) by one 10 s exercise period (Part II) where the ability to maintain power output was evaluated. Muscle biopsies were taken from m. vastus lateralis at rest, and immediately after (i) the fifth 6 s exercise period in Part I and (ii) the 10 s exercise period in Part II. In addition, a series of counter movement (CMJ) and squat (SJ) jumps were performed before and after the administration period.As a result of the creatine supplementation, total muscle creatine [creatine (Cr) + phosphocreatine (PCr)] concentration at rest increased from (mean + SEM) 128.7 (4.3) to 151.5 (5.5)mmolkg_1dry wt (P<0.05). This was accompanied by a 1.1 (0.5) kg increase in body mass (P<0.05). After the fifth exercise bout in Part I of the exercise protocol, PCr concentration was higher [69.7 (2.3) vs. 45.6 (7.5) mmol kg“‘ dry wt,P<0.05], and muscle lactate was lower [26.2 (5.5) vs. 44.3 (9.9) mmol kg”1dry wt,P<0.05] after vs. before supplementation. In Part II, after creatine supplementation, subjects were better able to maintain power output during the 10‐s exercise period (P0.05).These findings show that enhanced fatigue resistance during short duration high‐intensity exercise following creatine supplementation is associated with a greater availability of PCr and a lower accumulation of lactate in the muscle. The finding that jump performance was not enhanced suggests that short‐term creatine feeding does not influenc

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1995.tb09914.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Seven healthy males were exposed to quiet standing (15 min) after supine rest. Alterations in the total mass of plasma proteins were analysed from changes in plasma volume (PV; determination of control PV and subsequently of induced per cent PV changes using Hb/Hct) and protein concentration as revealed in arterial blood collected after standing. This approach adopted the concept that valid data on overall circulatory haemoconcentrations prevailing on standing can only be reached when blood is sampled on resumption of the recumbent posture, whereas conventional sampling from the standing subject provides erroneous information. The PV reduction on standing averaged 649 ± 65 mL (16.9 ± 1.0%). There were very similar net decreases in plasma (serum) total protein (7.6 ± 0.8 g) and albumin (7.8 ± 0.9 g). These findings permitted the following main conclusions of physiological and methodological pertinence: (1) Quiet standing leads to a clear‐cut net decrease in the plasma protein content predominantly confined to albumin, in all probability via convection secondary to PV loss by filtration in dependent regions. (2) It is suggested that the albumin loss reflects a quite high capillary macromolecular permeability in the dependent limbs on standing preferentially confined to skin/subcutaneous tissues. (3) The albumin loss implies that plasma concentration changes of neither albumin nor of total protein can be used to describe the PV loss on standing. However, concentration changes of the plasma globulin fraction as a whole, expressed by the difference (total protein –albumin), seem to reflect PV alterations approx

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1995.tb09915.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The marine flagellatePrymnesium patelliferumproduces toxins lethal to fish. The toxin extracted from the alga has haemolytic, cytotoxic and neurotoxic effects, but the action mechanisms of the toxin are not known in detail. We have examined the toxin effects on the voltage sensitive Ca2+‐currents, the cytosolic Ca2+‐level ([Ca2+]1) and the prolactin release in clonal rat anterior pituitary GH4C1cells, which possess T‐ and L‐type Ca2+‐channels. The trans‐membrane Ca2+‐current was recorded using whole‐cell voltage clamp. After 5–15 min exposure to the algal toxin at a final concentration of 50000–100000 cells mL‐1, the Ca2+‐currents through both the T‐ and L‐channels showed a 2–3‐fold enhancement. The voltage sensitivity of the Ca2+‐currents was not affected by the algal toxin, and the toxin‐induced currents were inhibited by 100μM of the Ca2+‐channel blocker D‐600. In toxin‐exposed cells microfluorometric measurements based on fura‐2 revealed an increase of [Ca2+]1from 100–150 to 300–500 nM. This elevation was delayed and partially inhibited by 100 μM D‐600. The algal toxin induced prolactin release in a dose‐dependent manner, and this effect was inhibited by the Ca2+‐channel blocker verapamil. We therefore conclude that the toxin ofP. patelliferumaffects the Ca2+homeostasis of the pituitary cells by increasing the leak through voltage sensitive Ca2+‐channels,

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1995.tb09916.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The role of cholinergic nerves in the cyclic activation of interdigestive motility and secretion was studied in 23 healthy volunteers. Net fluid transport in a distal duodenal segment and the release of pancreaticobiliary secretions into the duodenal lumen, were measured with a triple lumen perfusion technique. Interdigestive motor activity was recorded with a low‐compliance pneumohydraulic system, and the transmural potential difference (PD) was measured as an on‐line marker of electrogenic anion secretion. Transport parameters were related to the migrating motor complex (MMC) in the control situation and after the administration of atropine (0.01 mg kg‐1body wt, i.v.).The early part of the MMC cycle was characterized by low motor activity, low release of bile and pancreatic juice into the duodenal lumen, a slightly lumen positive transmural PD, and a non‐significant net fluid absorption (‘absorptive mode’)‐ Under control conditions, motor activity and pancreaticobiliary secretions subsequently increased and there was a shift in net fluid transport and transmural PD in the secretory direction (‘secretory mode’). Furthermore, there was a significant correlation between contraction frequency, a more lumen negative PD, and the magnitude of net fluid secretion. After the administration of atropine, the secretory mode was abolished, but there was still a significant correlation between contraction frequency and transmural PD.In conclusion, cholinergic neurones seem to mediate the shift from the absorptive to the secretory mode in the human distal duodenum. The antisecretory effect of atropine may be the result of inhibition of motilin release, reduced activation of tension‐sensitive intramural secretory pathways, or blockade of cholinergic neurones to the s

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1995.tb09917.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

We investigated the rate of tension development (ktd) after photolytical release of ATP from,P3‐l‐(2‐nitrophenyl)‐ethyladenosine‐5′‐triphosphate (‘caged ATP’) of atrial and ventricular fibre bundles from pig. Contraction was initiated from high‐tension (HT) and low‐tension (LT) rigor at maximal Ca2+activation (pCa 4.5). Thektdof atrial fibre bundles was 6.8 s_1from LT and 6.9 s_1from HT rigor. Rate of tension development of ventricular fibre bundles was significantly lower (P<0.001) being 1.06 s“1and 0.94 s”1from LT and HT rigor, respectively. Thektdof skinned ventricular fibre bundles incubated in a high [K+], low [Ca2+] (cardioplegic) solution prior to the skinning procedure decreased significantly (P<0.05) to 0.73 s‐1and 0.63 s_1from LT and HT rigor, respectively, whereas that of skinned atrial fibre bundles remained at 7.1 s‐1and 6.9 s‐1from LT and HT rigor, respectively. Phosphorylation levels of the myosin light chain 2 isoform in the atrial fibre bundles (ALC‐2) was 15.6±2.7%. The corresponding values for the two ventricular isoforms, VLC‐2 and VLC‐2*, were 31.2 ± 0.4% and 25.1 ±2.1%, respectively. Phosphorylation levels of fibre bundles incubated in cardioplegic solution prior to skinning were 11.6%, 18.9%, and 15.4% of the ALC‐2, VLC‐2 and VLC‐2*, respectively. The results show that the rate of tension development is more than seven‐fold higher in the atrial compared with ventricular fibre bundles. These results correlate with the differences in ATPase activity of the contractile proteins in solution and, most likely, reflect differences in the myosin isoform composition. In ventricular fibre bundles the increased levels of light chain phosphorylation we

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1995.tb09918.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Effects of the naturally occurring polyamine spermine on electrical and contractile properties of the rat portal vein were studied. 1 mM spermine nearly abolished spike activity and spontaneous contractions and decreased the intracellular Ca2+concentration ([Ca2+],). The phasic force responses to 0.1 and 1 μM phenylephrine were partially inhibited, but not the sustain plateau contraction caused by 5/IMphenylephrine. The Ca2+‐force relation in high‐K+(128 mM)‐depolarized veins was shifted to the right, EC50for Ca2+increasing from 0.50 ± 0.03 mM (control,n= 8) to 0.65 ± 0.06 and to 0.94 ± 0.03 at 1 (n –4) and 10 (n =3) mM spermine, respectively. However, at a Ca2+concentration of 2.5 mM, giving maximal force, there was no effect of spermine (1 mM) on either force or [Ca2+],. Whereas extracellular spermine thus reduced contractile activity at moderate levels of stimulation, increased intracellular concentration of spermine potentiated the force response to Ca2+. Intracellular loading of spermine by reversible permeabilization increased its concentration by 2–3 times. The spontaneous activity and response to phenylephrine were unchanged. However, the Ca2+‐force relation of depolarized veins was shifted to the left, EC50decreasing from 0.51 ± 0.04 mM in controls (n= 7) to 0.36 ± 0.02 mM in the loaded veins (n= 9). Spermine increased Ca2+‐activated force in portal veins permeabilized with β‐escin. The degree of potentiation was consistent with observed effects in spermine‐loaded intact veins. The results suggest that spermine at physiological intracellular concentration may contribute to the determination of Ca2+sensitivity in vasc

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1995.tb09919.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Modulation of the L‐type calcium channel by catecholamines improves action potential parameters in single ventricular myocytes depolarized by high [K+]0Tyrode. Whether this modulation is important in offsetting the negative effects of hyperkalaemia in the whole heart is not known. We tested the effects of the calcium channel antagonist, verapamil, on restoration of cardiac performance by adrenergic stimulation in high [K+]0in anaesthetized rabbits and isolated perfused working rabbit hearts. Raised [K+]0decreased SBP, LVP and LVdP/dtmaxin vivo([K+]a8.6 ± 0.2 mM;n= 10) and aortic flow (AF) in the isolated heart (8 mM [K+]0Tyrode;n= 25). However, the negative effects of raised [K+]awere offset by isoprenaline (Iso, 1 μg kg‐1min‐1i.v.)in vivoand by noradrenaline (NA, 80 nM) in the isolated heart. Verapamil (0.15 mg kg‐1iv.; 15 nM isolated heart) markedly potentiated the negative inotropic effects of raised [K+]nin both preparations. Verapamil attenuated the effect of isoprenalinein vivobut in the isolated heart, the protective effect of NA in 8 mM [K+] Tyrode (AF 97 ± 10 mL min1in 8 mM [K+]0compared with AF 141 ± 8.5 mL min‐1in 8 mM [K+]0+ NA) was offset by the drug (90±8mL min‐1in 8 mM [K+]0+ NA + V). Furthermore, verapamil abolished aortic flow in 8 mM [K+]0alone. These findings suggest that the heart may be critically dependent on modulation of intracellular calcium in order to tolerate concentrations of K4similar to those seen during a short burst of intensive exerci

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1995.tb09920.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The intensity‐response (V/logI) function of ERG OFF response (d‐wave) in dark and light adapted superfused frog eyecups was investigated before and after blockade of the retinal ON channel by 2‐amino‐4‐phosphonobutyrate (APB). TheV/logIfunction of the dark adapted d‐wave had two distinct components, each of them consisting of an ascendent and descendent part. In eyes adapted to mesopic or photopic background the V/logIfunction had only one component. It was shifted to the right along the intensity axis, had a steeper slope and a higher maximal response amplitude compared with the two components of the dark‐adaptedV/logIcurve.Perfusion with 200 μmol APB markedly increased the d‐wave amplitude at all stimulus intensities except for the threshold ones in both dark and light adapted eyes. The position of theV/logIcurve was shifted slightly to the left along the intensity axis in dark adapted eyes, but was not changed in light adapted eyes. Thus the adaptational mechanism responsible for changes in the decremental sensitivity with increased background illumination was not altered by APB.The effect of APB was studied also in chromatically adapted eyes, in which the responses were predominantly mediated by one photoreceptor type. The results showed that the potentiating effect of APB on d‐wave did not depend on p

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1995.tb09921.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY