摘要:

The effect of bovine serum albumin (BSA) on the activity of the calcium release channel of the sarcoplasmic reticulum from rabbit skeletal muscle was investigated using both tension recording from skinned fibres and electrophysiological recording of unitary channel currents from planar lipid membranes. BSA had no effect on the Ca2+affinity of the contractile proteins, elicited no tensionper sein Ca2+‐loaded skinned fibres, but potentiated caffeine‐induced tension. Maximum potentiation was observed with 0.05–0.5% BSA. BSA (0.1%) had no detectable effect on the basal activity of the Ca2+‐release channel incorporated in lipid bilayer. However, channel stimulation elicited by either caffeine (2 mM) or ATP (60 μM) was further enhanced by BSA (0.1%), as indicated by significant increases in Po, the open probability of the channel. These results suggest that BSA can modulate the response of the skeletal muscle SR Ca2+‐release channel to different activators such as ca

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00140.x

出版商:Blackwell Science Ltd.    

年代:1997

数据来源: WILEY

摘要:

The potent vasoconstrictor substances, 5‐hydroxytryptamine (5‐HT), angiotensin II (A II), and bradykinin bind to G‐protein coupled receptors and activate phospholipase C‐β. Using the Fura‐2 technique and microfluorometry we found that all three agonists induce a transient increase in intracellular calcium ([Ca2+]i) by releasing stored calcium in human renal artery smooth muscle cells. Using binding of [3H]‐phorbol dibutyrate (PDBu) to quantify membrane‐associated protein kinase C (PKC) we also showed that 5‐HT, A II and bradykinin induced a rapid but transient translocation of protein kinase C (PKC) to the plasma membrane. The time‐course of the rise in [Ca2+]iwas similar to that of the increase in [3H]‐PDBu binding, suggesting transient activation of the calcium dependent α‐isoform of PKC. Following prolonged pre‐treatment with tetradecanoyl phorbol acetate (100 nmol L−1), which down‐regulates PKC‐α and δ, the angiotensin‐induced PKC translocation was lost. 5‐HT, A II or bradykinin were unable to increase cell proliferation or act as a co‐mitogens with platelet‐derived growth factor in human vascular smooth muscle cells. Thus, transient increases in [Ca2+]ior PKC activity by a vasoconstrictor agent are insufficient to

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00157.x

出版商:Blackwell Science Ltd.    

年代:1997

数据来源: WILEY

摘要:

Electrical field stimulation (EFS) produced relaxation of contracted arteries in the presence of tetrodotoxin. In the present study the contributions of vascular smooth muscle repolarization and endothelial release of nitric oxide to the relaxation response were investigated using isolated rat tail arteries and bovine aortic endothelial cells (BAEC). Intact and endothelium‐denuded rings or intact, pressurized artery segments were contracted with either phenylephrine or KCl prior to EFS. Electrical field stimulation induced a small relaxation in denuded, phenylephrine contracted rings that was inhibited by the K+channel blockers glibenclamide and BaCl2In intact, phenylephrine‐contracted rings, EFS induced significantly larger relaxations that were inhibited by BaCl2as well as byLNAME, an inhibitor of nitric oxide (NO) synthase, and methylene blue. EFS‐induced relaxations were completely inhibited when BaCl2andL‐NAME or methylene blue were combined. Exposure to Ca2+‐free buffer or diltiazem also inhibited the relaxation while ascorbic acid had no effect. Effluent from electrically stimulated BAEC caused denuded, phenylephrine contracted rings to relax. The ability of the effluent to cause relaxation was almost completely blocked by exposure of the BAEC toL‐NAME or exposure of the recipient vascular smooth muscle to methylene blue; glibenclamide caused partial blockade. Simultaneous measurements of membrane potential and intraluminal pressure showed that EFS‐induced membrane repolarization preceded changes in steady‐state pressure. It is concluded that (1) the smooth muscle cells possess an endothelium‐independent repolarization mechanism, (2) EFS causes endothelial cells of intact arteries to release NO and possibly a hyperpolarizing factor, (3) EFS of BAEC causes release of NO, and (4) EFS‐induced relaxation depends on vascular smooth muscle cell membrane repolarization and endothelial cell release of va

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00141.x

出版商:Blackwell Science Ltd.    

年代:1997

数据来源: WILEY

摘要:

Heart basal metabolism has been classically studied as the energy expenditure of those processes unrelated to mechanical activity and often measured by rendering the heart inactive using cardioplegic solutions (usually by increasing extracellular K concentration ([K]e). In arterially perfused rat heart (at 25 °C), raising [K]e from 7 to 25 mMat a constant extracellular Ca concentration ([Ca]e) (0.5 mM), induced an increase in resting heat production (Hr) from 4.1 ± 0.3 to 5.1 ± 0.3 mol. wt g−1. Under 25 mMK additional increase in [Ca]efurther increased Hr to 6.0 ± 0.4, 7.0 ± 0.4 and 8.3 ± 0.9 mol. wt g−1for 1, 2 and 4 mMCa, respectively. While under 7 mMK perfusion Hr was not affected by 4 μMverapamil, under 25 mMK and 2 mMCa 0.4 μMverapamil induced a decrease in Hr (−1.6 ± 0.2 mol. wt g−1,n = 5,P < 0.001). Caffeine increased Hr under 0.5 mMCa and 7 mMK perfusion (+0.32 ± 0.06 and +1.19 ± 0.25 mol. wt g−1for 1 and 5 mMcaffeine respectively), but under 25 mMK conditions Hr was not affected by caffeine 2 mM. Severe hypoxia decreased Hr under both 7 and 25 mMK (3.7 ± 0.5 to 2.7 ± 0.4 mol. wt g−1and 7.0 ± 0.4 to 2.2 ± 0.5 mol. wt g−1, respectively) suggesting that the increased Hr associated with the verapamil sensitive fraction of heat released is associated to a mitochondrial mechanism. Therefore, the use of high [K]eoverestimates basal values by increasing a verapamil sensitive fraction

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00137.x

出版商:Blackwell Science Ltd.    

年代:1997

数据来源: WILEY

摘要:

The effects of age and gender on heart rate variability as measured by spectral and time domain analysis of 24 h ECG recordings were evaluated in 101 healthy subjects, 49 men and 52 women (20‐69 years of age). In the frequency domain, total power, very low‐frequency power, low‐frequency power and high‐frequency power were negatively correlated to age (P<0.001 for all variables). Total power decreased by 30% between 20‐29 and 60‐69 years of age. In the time domain, SDNN‐index, the mean of the standard deviations of all normal R‐R intervals for all 5 min segments of a 24 h ECG recording, was negatively correlated to age (P<0.001). Total power, very low‐frequency power, low‐frequency power and the low‐frequency/high‐frequency ratio were lower in women (P<0.05, P<0.05, P<0.01 and P<0.01), although the absolute differences were much smaller than for age. There was a pronounced circadian variation; at night total power increased in all age groups (P<0.01). The results show that age, and to a lesser degree gender, are important determinants of heart rate variability in healthy subjects. Heart rate variability is a valuable tool for risk stratification in cardiovascular disease, but the physiological effects of ageing, with diminishing heart rate variability in older age groups, must als

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00142.x

出版商:Blackwell Science Ltd.    

年代:1997

数据来源: WILEY

摘要:

The effects of chronic cold exposure on soleus muscle capillarity were examined, particularly in terms of the distribution of arteriolar and venular capillaries and their capillary domain area (CDA) in adult rats exposed to cold for 68 generations (CG;n = 6). These parameters were compared with those obtained from control rats (CON;n = 5) and deacclimatized rats (DCG;n = 4), reared in thermoneutral temperature after being reared for 11 generations in cold. Morphometric data were obtained from muscle cross sections exposed to a double‐staining method that stained the arteriolar and venular portions of capillaries blue and red, respectively. In CG, the capillary densities of arteriolar and venular capillaries were significantly greater than that of both CON and DCG (P < 0.05). The CDA of arteriolar, intermediate and venular portions in CG was significantly smaller by 15, 14 and 13%, respectively, than those of respective portions in CON (P < 0.05). Although CDA of arteriolar and venular capillary portions was also smaller in DCG than in CON, the degree of reduction was less in DCG than in CG. The succinate dehydrogenase activity of soleus muscle was significantly greater in CG than in both CON and DCG (P < 0.05). These results suggest that adaptive changes in the oxygen transport system, identified as an increase in the number of arteriolar capillaries and a reduction in the diffusion distance for oxygen, were observed in the soleus muscle after chronic cold exposure. These changes may improve the effective oxygen supply to muscle tissues and enable muscle tissues to promote thermogenes

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00136.x

出版商:Blackwell Science Ltd.    

年代:1997

数据来源: WILEY

摘要:

Dynamic exercise increases the transcranial Doppler determined mean blood velocity in basal cerebral arteries corresponding to the cortical representation of the active limb(s) and independent of the concomitant rise in the mean arterial pressure. In 12 rowers we evaluated the middle cerebral artery blood velocity response to ergometer rowing when regulation of the cerebral perfusion is challenged by stroke synchronous fluctuation in arterial pressure. Rowing increased mean cerebral blood velocity (57 ± 3 to 67 ± 5 cm s−1; mean ± SE) and mean arterial (86 ± 6 to 97 ± 6 mmHg) and central venous pressures (0 ± 2 to 8 ± 2 mmHg;P < 0.05). The force on the oar triggered an averaging procedure that demonstrated stroke synchronous sinusoidal oscillations in the cerebral velocity with a 12 ± 2% amplitude upon the average exercise value. During the catch phase of the stroke, the mean velocity increased to a peak of 88 ± 7 cm s−1and it was in phase with the highest mean arterial pressure (125 ± 14 mmHg), while the central venous pressure was highest after the stroke (20 ± 3 mmHg). The results suggest that during rowing cerebral perfusion is in

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00144.x

出版商:Blackwell Science Ltd.    

年代:1997

数据来源: WILEY

摘要:

The purpose of this study was to determine forearm blood flow changes during static handgrip exercise at different intensities in relation to heart rate and blood pressure. Seven active women performed static handgrip exercise at intensities of 10, 30, 50 and 70% maximum voluntary contraction (MVC) in a supine position for 1 min. During exercise at different intensities, the brachial arterial blood flow (Doppler ultrasound method), calculated from vessel diameter, flow velocity and heart rate (measured by ECG), increased to a similar level (137.3 ± 20.2 – 160.9 ± 26.1 mL min−1) from pre‐exercise control value (87.5 ± 14.1 mL min−1). These increases at the lower intensities were attributable to increased in‐flow during one cardiac cycle, whereas at the higher intensities, they were due to increased heart rate. Both systolic and diastolic blood pressure (Finapres) changes increased from 10% MVC (16.1 ± 3.4, 9.0 ± 1.7 mmHg) up to 50% MVC (33.8 ± 6.7, 25.0 ± 4.9 mmHg), but were disproportionately more elevated at 70% MVC (46.1 ± 7.9, 42.9 ± 8.9 mmHg), suggesting neural vasoconstriction had occurred. Immediate post‐exercise hyperaemia, used as an indicator of poor blood supply, became greater as the exercise intensity increased. These results suggest that the brachial arterial blood flow was maintained at a similar level during 60‐s static handgrip exercise at different intensities by elevating the blood pressure and heart rate, which probably counteracted the increased intramuscular pressure and neural vasoconstriction occurring at the higher exercise intensity. The magnitude of the post‐exercise hyperemic response increased as exercise level increased despite increased blood flow to the arm during exercise. This suggests a worsening imba

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00158.x

出版商:Blackwell Science Ltd.    

年代:1997

数据来源: WILEY

摘要:

The objective of this work was to study cell volume regulation and transepithelial transport in renal proximal tubules. A modified stop‐flow technique inin vitroperfused renal proximal tubules ofCarassius auratuswas used. The rate of luminal fluid absorption and the epithelial thickness were measured. Isosmotic Na+removal from the tubule lumen or addition of the Na+/glucose co‐transport blocker phloridzin (0.5 mM) to the lumen inhibited fluid absorption. Only minor effects on luminal absorption were observed following: (1) addition of the K+channel inhibitor BaCl2(1 mM); (2) addition of the Cl−channel inhibitor MK‐196 (1 mM); (3) lowering bath and perfusate HCO3−in the presence of 0.1 mMacetazolamide; or (4) addition of the leukotriene‐D4receptor antagonist L‐660, 711 (20 μM). Isosmotic addition of 40 mMtaurine to the bath inhibited the rate of fluid absorption. This effect could be partially overcome with the organic acid secretion inhibitors probenecid (1 mM) and bromcresol green (0.1 mM). Finally, administration of the 5‐lipoxygenase antagonist ETH 615–139 (20 μM) caused a significant reduction in the rate of luminal absorption. In summary, tubular reabsorption is, in this preparation, closely linked to sodium reabsorption. In the absence of luminal amino acids most of this sodium uptake seems to occur in co‐transport with glucose followed by osmotically obligated water. Eicosanoids from the 5‐lipoxygenase pathway appear to regulate this process. Finally, high concentrations of taurine in the bath opposed luminal fluid absorption, at least partial

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00155.x

出版商:Blackwell Science Ltd.    

年代:1997

数据来源: WILEY

摘要:

The occurrence of angiotensin converting enzyme (EC 3.4.15.1; ACE) was demonstrated for the first time in serum of newt (Triturus carnifex) and frog (Rana esculenta). The enzymatic activity was evidenced following hydrolysis of N‐[3‐(2‐furyl) acryloyl]L‐phenylalanyl glycyl glycine (FAPGG), a synthetic substrate of ACE. The serum enzyme liberated N‐[3‐(2‐furyl) acryloyl]L‐phenylalanine (FAP) from FAPGG. The properties of the amphibian serum enzymes were compared with those of swine. The amphibian serum FAPGG hydrolysing activities were inhibited by typical ACE inhibitors, captopril and lisinopril. The optimum of pH was 8.3 at 10 and 37 °C and the temperature optimum was 45 °C. The values were similar to those of swine serum. The FAPGG Michaelis‐Menten constants (Km) at 37 °C of amphibian serum enzymes (0.337 mmand 0.282 mmfor frog and newt, respectively) were lower than that of swine (1.305 mm), but close to human serum enzyme. The Km values obtained at 10 °C were lower than those at 37 °C (0.152, 0.086, and 1.029 mmfor frog, newt, and swine serum, respectively). Amphibian sera hydrolysed bullfrog synthetic angiotensin I to produce angiotensin II. Captopril (50 μ

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00147.x

出版商:Blackwell Science Ltd.    

年代:1997

数据来源: WILEY