摘要:

H+ions are generated rapidly when muscles are maximally activated. This results in an intracellular proton load. Typical proton loads in active muscles reach a level of 20–25 μmol∙g−1, resulting in a fall in intracellular pH of 0.3–0.5 units in mammalian muscle and 0.6–0.8 units in frog muscle. In isolated frog muscles stimulated to fatigue a proton load of this magnitude is developed, and at the same time maximum isometric force is suppressed by 70–80%. Proton loss is slowed when external pH is kept low. This is paralleled by a slow recovery of contractile tension and seems to support the idea that suppression results from intracellular acidosis. Nonfatigued muscles subjected to similar intracellular proton loads by high CO2levels show a suppression of maximal tension by only about 30%. This indicates that only a part of the suppression during fatigue is normally due to the direct effect of intracellular acidosis. Further evidence for a component of fatigue that is not due to intracellular acidosis is provided by the fact that some muscle preparations (rat diaphragm) can be fatigued with very little lactate accumulation and very low proton loads. Even under these conditions, a low external pH (6.2) can slow recovery of tension development 10-fold compared with normal pH (7.4). We must conclude that there are at least two components to fatigue. One, due to a direct effect of intracellular acidosis, acting directly on the myofibrils, accounts for a part of the suppression of contractile force. A second, which in many cases may be the major component, is not dependent on intracellular acidosis. This component seems to be due to a change of state in one or more of the steps of the excitation–contraction coupling process. Reversal of this state is sensitive to external pH which suggests that this component is accessible from the outside of the cel

ISSN:0008-4212    

DOI:10.1139/y85-072

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

We describe the functional characteristics of a new primary culture system derived from a suspension of dog proximal tubular cells. The culture system is maintained on alpha minimal essential medium with 15% fetal calf serum supplementation. At confluency the cultured cells demonstrate the following: (i) typical epithelial morphology using light microscopy, with multiple dome formation inhibited by ouabain; (ii) strong binding with a polyclonal antibody directed against dog proximal tubular brush border membrane antigens; (iii) high concentration of alkaline phosphatase activity by histochemical staining; and (iv) 25-hydroxycholecalciferol (25(OH)D3)-24-hydroxylase activity. Sugar transport was assessed using α-methyl-D-glucopyranoside (αMG), a nonmetabolizable analog ofD-glucose, as well asL-glucose, and 3-O-methyl-D-glucose (3OMG). The transport of αMG was stereospecific; temperature sensitive; inhibited strongly by phlorizin but not by cytochalasin B, phloretin, or 3OMG; and Na dependent. The transport of 3OMG is stereospecific, temperature sensitive, and inhibited strongly by phloretin and cytochalasin B, but not by phlorizin. Despite the apparent heterogeneity of cell type, this primary culture system exhibits many features of normal dog proximal tubule function.

ISSN:0008-4212    

DOI:10.1139/y85-073

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The influence of prolonged exposure of guinea pigs to excessive ascorbic acid (AA) on the outcome of pregnancy, as well as the adaptive effect of the vitamin either during preweanling life or following weaning, were examined. Continuous exposure to AA (1 mg/mL drinking water) from the time they were first mated up to the time of second pregnancy, had no significant effect on the number of offspring and on their weights at birth, when compared with that of the animals receiving 0.1 mg AA/mL drinking water. However, change in AA intake from 1 to 0.1 mg/mL drinking water, at the age of 21 days, resulted in a significant loss in body weight and reductions in the plasma, leucocyte, and adrenal concentrations of AA, as compared with those of the pair-fed animals receiving 0.1 mg/mL drinking water throughout. The present study also indicated that the conditioning effect is less pronounced in guinea pigs when exposed to the high AA following weanling age than in utero.

ISSN:0008-4212    

DOI:10.1139/y85-074

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Male Swiss Webster mice, treated withN-acetylcysteine (NAC, 500 mg/kg po) 1 h following acetaminophen (NAPA, 350 mg/kg po) administration, had control levels of transaminases indicating that NAC protects against NAPA-induced hepatotoxicity by postabsorption antidotal mechanism(s). Hepatic congestion induced by NAPA was reduced by NAC. Significantly higher elimination rate constants (K) for indocyanine green (500 μg/kg, iv) in mice treated with NAPA and NAC (K = 0.676 ± 0.062) than in animals receiving NAPA alone (0.341 ± 0.105) suggested NAC improved or preserved the hepatic circulation of the compromised liver. This NAC-induced improvement and (or) preservation of hepatic circulation was reflected in biliary and urinary excretion of acetaminophen and its metabolites by a general increase in elimination during the first 6 h (70.2 ± 2.6 vs. 32.6 ± 7.1%), and in the repletion of glutathione (GSH) in the liver by a return to control levels more quickly (3 vs. >5 h) following depletion by NAPA. The metabolic consequence of the postabsorption antidotal effect of NAC in the compromised liver was a preferential excretion of sulphydryl-derived metabolites in the 1–4 h bile (GSH conjugate 11.30 ± 1.25 vs. 7.25 ± 0.39%) which was subsequently observed in the urine by preferential excretion of glutathione degradation products.

ISSN:0008-4212    

DOI:10.1139/y85-075

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Methyltetrazolethiol (1-methyl-5-mercapto-1,2,3,4-tetrazole, MTT) is a heterocyclic substituent of the cephalosporin antibiotics, cefamandole, cefoperazone, and moxalactam. Pretreatment of rats with MTT has been reported to increase blood acetaldehyde concentration after ethanol administration. The time course of MTT-induced inhibition of hepatic aldehyde dehydrogenases (ALDH) was determined in adult, male Sprague–Dawley rats in comparison with the hepatic ALDH inhibition induced by calcium carbimide (calcium cyanamide, CC) and disulfiram (D). The apparent onset of maximal inhibition of hepatic lowKmALDH occurred at 2 h for 50 mg/kg MTT (subcutaneous, s.c.) and 7 mg/kg CC (oral) and at 24 h for 300 mg/kg D (oral). The relative magnitude of maximal inhibition of lowKmALDH was CC > D > MTT. The relative duration of enzyme inhibition was D > MTT > CC. HighKmALDH was only inhibited by CC. Hepatic lowKmALDH was selectively inhibited by s.c. and oral administration of 125 mg/kg MTT. For s.c. administration of 125 mg/kg MTT, the magnitude of maximal enzyme inhibition and the duration of inhibition were greater than for the 50 mg/kg dose. Oral administration of 125 mg/kg MTT produced similar inhibition of hepatic lowKmALDH compared with s.c. administration of the same dose. The time course of blood ethanol and acetaldehyde concentrations was determined for the intravenous infusion of two 0.3-g/kg doses of ethanol to rats that were pretreated orally with saline (1 h), MTT (125 mg/kg, 2 h), or CC (7 mg/kg, 1 h). The relative increase in blood acetaldehyde concentration compared with saline pretreatment was CC > MTT. The elimination of ethanol from blood was slower in the MTT- and CC-pretreated animals, and this effect was more pronounced for CC pretreatment. Overall, the data demonstrate that the characteristics of hepatic ALDH inhibition for MTT are different from those of the known ALDH inhibitors, CC and D.

ISSN:0008-4212    

DOI:10.1139/y85-076

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The effect of three different subgroups of benzodiazepines on the indirectly evoked twitch tension was investigated in the in vitro rat phrenic nerve – hemidiaphragm preparation. Two effects were observed: an initial increase in twitch tension at lower concentrations with some benzodiazepines, and a concentration-dependent depression at higher concentrations with all benzodiazepines. Significant differences for these effects were observed among the three subgroups of benzodiazepines and additionally within the subgroup of the 1,4-benzodiazepine-2-ketones. Structural requirements for both effects were different. For the increase of twitch tension a —CH3substitution at R1and a —F substitution at R2′were beneficial. For the twitch depression an —OH substitution at R3and a —Cl substitution at R2′were optimal. An interaction between substituents at different substitution sites occurred. The potency of twitch depression showed a good correlation with literature reports of pKavalues and a poor-to-inverse correlation with lipophilicity indices. A benzodiazepine antagonist, Ro 15-1788, caused no change in twitch tension in the concentration range of the investigated benzodiazepines nor did it prevent the twitch depression caused by benzodiazepines.

ISSN:0008-4212    

DOI:10.1139/y85-077

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The adenosine derivative, 2′3′-di-O-nitro-(5′-N-ethylcarboxamido)adenosine (DINECA), caused relaxation in several isolated smooth muscle preparations including guinea pig taenia caeci, beef coronary arteries, and rabbit small intestine. In rabbit small intestine the response profile of DINECA action differed from that of established adenosine receptor agonists and, in contrast with the latter, its relaxant effect was only partially reversed by the antagonist 8-p-sulfophenyltheophylline. Concentration–response curves to 5′-(N-ethylcarboxamido)adenosine (NECA), but not those to DINECA, were significantly shifted to the right by 100 μMof 8-sulfophenyltheophylline. Tissues exposed previously to DINECA became refractory to adenosine, an effect not observed with tissues exposed to NECA, suggesting that DINECA became bound to adenosine receptors. Adenylate cyclase from neuroblastoma cells, containing Ra-type adenosine receptors, was stimulated by 2-chloroadenosine and NECA but not by DINECA. The results suggest that most of the smooth muscle relaxant actions of DINECA are not due to interaction with adenosine receptors but are probably due to its function as a nitrate. However, DINECA appears to interact with adenosine receptors, causing long lasting inhibition of adenosine action in rabbit intestine. Such actions may contribute to the overall response to DINECA application in vivo, although lowering of blood pressure due to the high reactivity of the vasculature to nitrates may be the initial and major effect.

ISSN:0008-4212    

DOI:10.1139/y85-078

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The actions of a series of 15 Ca2+channel antagonists including D-6(X), nifedipine, and diltiazem were examined against K+depolarization and muscarinic receptor induced responses in guinea pig bladder smooth muscle. Responses of bladder are very dependent upon extracellular Ca2+and sensitive to the Ca2+channel antagonists, the tonic component more than the phasic component of response. Regardless of stimulant, K+or methylfurmethide (MF), or component of response, the same rank order of antagonist activities is expressed, suggestive of a single structure–activity relationship and the existence of a single category of binding site which may, however, exist in several affinity states. High affinity binding of [3H]nitrendipine (KD = 1.1 × 10−10 M) occurs in bladder membranes, and similar high affinity binding was found in microsomal preparations from other smooth muscles including guinea pig and rat lung, rat vas deferens, uterus, and stomach. [3H]nitrendipine binding in the bladder was sensitive to displacement by other 1,4-dihydropyridines, paralleling their pharmacologic activities and showing excellent agreement with binding data previously obtained for guinea pig ileal smooth muscle. Comparison of pharmacologic data for inhibition of K+- and MF-induced responses by a common series of Ca2+channel antagonists in bladder and ileum revealed excellent correlations. Neither pharmacologic nor binding studies suggest significant differences in Ca2+channel antagonist properties in smooth muscle from bladder and intestine.

ISSN:0008-4212    

DOI:10.1139/y85-079

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The effects of a spike concentration of growth hormone (GH) on hepatic portal and peripheral levels of free serotonin and catecholamines were studied by improved radioenzymatic methods in trained, conscious, normal, adult dogs fitted with an indwelling portal catheter. An injection of ovine GH (6 or 100 μg/kg) into a cephalic vein produced in the hepatic portal circulation a transient, statistically significant rise of serotonin and a concomitant significant reduction in the concentration of dopamine, norepinephrine, and epinephrine. No change was found in the peripheral circulation, partly because the amines were conjugated to sulfates and glucuronides and these derivatives are not detectable by our assays. Thus, a pulse of GH not only stimulates the release of pancreatic hormones and glucose turnover, but also affects the portal profile of glucoregulatory bioamines. The present investigation lends further support to our view that the splanchnic area represents an endocrine system whose preferential target is the liver.

ISSN:0008-4212    

DOI:10.1139/y85-080

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

We have studied the effects of acetaminophen metabolites generated by a murine hepatic microsomal system on lymphocytes from two subjects heterozygous for glutathione synthetase deficiency. Heterozygous cells exhibited greater dose-related toxicity than controls. Following a 2-h incubation with acetaminophen and the microsomal system, cells were washed and incubated for 16 h in the presence or absence ofN-acetylcysteine, the standard antidote for acetaminophen toxicity. In control cells, glutathione content was replenished to nearly base-line values and toxicity was prevented.N-Acetylcysteine thus prevented toxicity even after covalent binding of acetaminophen metabolites had occurred. Heterozygous cells failed to useN-acetylcysteine as efficiently to resynthesize glutathione, and the cells were not protected from acetaminophen toxicity. Heterozygotes may be at increased risk of toxicity from drugs whose metabolites are detoxified by glutathione conjugation.

ISSN:0008-4212    

DOI:10.1139/y85-081

出版商:NRC Research Press    

年代:1985

数据来源: NRC