Components of cholinergic excitation coupling with smooth muscle contraction in the guinea pig taenia coli]

In concentrations of 10(-9)-10(-7) g/ml acetylcholine increased the tone of the smooth muscles of the longitudinal band of the large intestine of a guinea pig, increasing the permeability of the cellular membranes for the entering flux of 45Ca2+. In concentrations of 10(-6) g/ml and over acetylcholine caused a release of the membranous calcium and in the concentrations of 10(-5)-10(-3) g/ml markedly increased the permeability of the membranes of the smooth muscle cells for the 22Na+ ions causing depolarization and an increase in the frequency of the action potentials. It is supposed that the coupling of the cholinergic stimulus with the end effect (muscle contraction) included 3 components: intensification of the entrance of Ca2+ into the smooth muscle cells, release of the membrane calcium and adhesion mechanism.     

Biosorption of Ni, Cr and Cd by metal tolerant Aspergillus niger and Penicillium sp. using single and multi-metal solution

Fungi including Aspergillus and Penicillium, resistant to Ni2+, Cd2+, and Cr6+ were isolated from soil receiving long-term application of municipal wastewater mix with untreated industrial effluents of Aligarh, India. Metal tolerance in term of minimum inhibitory concentration (MIC) was 125-550 microg/ml for Cd, 300-850 microg/ml for Ni and 300-600 microg/ml for Cr against test fungi. Two isolates, Aspergillus niger and Penicillium sp. were tested for their Cr, Ni and Cd biosorption potential using alkali treated, dried and powdered mycelium. Biosorption experiment was conducted in 100 ml of solution at three initial metal concentrations i.e., 2, 4 and 6 mM with contact time (18 hr) and pretreated fungal biomass (0.1g) at 25 degrees C. Biosorption of all metals was found higher at 4 mM initial metal concentration as compared to biosorption at 2 and 6 mM concentrations. At 4 mM initial metal concentration, chromium biosorption was 18.05 and 19.3 mg/g of Aspergillus and Penicillium biomasses, respectively. Similarly, biosorption of Cd and Ni ions was also maximum at 4 mM initial metal concentration by Aspergillus (19.4 mg/g for Cd and 25.05 mg/g of biomass for Ni) and Penicillium (18.6 mg/g for Cd and 17.9 mg/g of biomass for Ni). In general, biosorption of metal was influenced by initial metal concentration and type of the test fungi. The results indicated that fungi of metal contaminated soil have high level of metal tolerance and biosorption properties.     

Chromium(III) bound to DNA templates promotes increased polymerase processivity and decreased fidelity during replication in vitro

Carcinogenic chromium [Cr(VI)] compounds are reduced intracellularly to DNA- and protein-reactive chromium(III) species. However, the role of Cr(III) ions in chromium-induced genotoxicity remains unclear. We have investigated the effects of chromium(III) binding on DNA replication and polymerase processivity in vitro. Chromium ions bind slowly and in a dose-dependent manner to DNA. Micromolar concentrations of free chromium inhibit DNA replication, but if the unbound chromium is removed by gel filtration, the rate of DNA replication by polymerase I (Klenow fragment) on the chromium-bound template is increased greater than 6-fold relative to the control. This increase is paralleled by as much as a 4-fold increase in processivity and a 2-fold decrease in replication fidelity. These effects are optimum when very low concentrations of chromium ions are bound to the DNA [3-4 Cr(III) ions per 1000 nucleotide phosphates]. Increased concentrations of chromium lead to the production of DNA-DNA cross-links and inhibition of polymerase activity. These results suggest that low levels of DNA-bound chromium(III) ions may contribute to chromium mutagenesis and carcinogenesis by altering the kinetics and fidelity of DNA replication.     

Rat liver microsomal cholesterol biosynthesis and drug oxidase activity are affected by chromium ions (Cr3+) in vitro

Chromium ions (Cr3+)evoked a biphasic curve of changes of rat liver microsomal cholesterol biosynthesis using [14C]acetate and/or [14C]mevalonate as precursors. While for the lower range of Cr3+ concentrations the rate of cholesterol biosynthesis rises, at concentrations above 8 X 10(-6) M they evoke a decrease in the cholesterol biosynthesis, up to 50% down on its control value at a concentration of 8 X 10(-4) M. Differences were more pronounced when using [14C]mevalonate instead of [14C]acetate as precursor. The activity of the microsomal enzyme biphenyl-4-hydroxylase showed an equally intense rise to that of cholesterol biosynthesis up to a 8 X 10(-6) M Cr3+ concentration. Above this concentration, however, the activity of the enzyme starts to drop. NADPH-cytochrome c reductase and NADPH-oxidase were decreased at all Cr3+ concentrations used, which cover a 100-fold range. Lineweaver-Burk plots of the cytoplasmic glucose-6-phosphate dehydrogenase demonstrated an uncompetitive mechanism of inhibition by Cr3+ ions. The results are discussed in terms of the possible significance of the Cr3+ concentration-dependent effects on cholesterol biosynthesis, with the observed atherosclerosis in Cr-deficient humans.     

The direct depressant effect of LCB29 (idrocilamide) on mechanical tension of rat soleus muscle fibers

The effect of LCB29 was tested on twitch characteristics, tetanic tension, and K+ and voltage-clamp contractures of rat soleus muscle fibers. In concentrations ranging from 10(-6) to 5 x 10(-4) M, LCB29 simultaneously inhibited the twitch amplitude, the maximum rate of tension development, and the maximum rate of relaxation. In concentrations ranging from 10(-5) to 10(-4) M, tetanic tension (100 Hz, 1 s) was inhibited by the same amount. The effect of 5 x 10(-5) M LCB29 was studied on K+ contractures and contractures induced, under voltage-clamp conditions, by long-lasting depolarizations. Its effect was significantly stronger than those on twitch and tetanic tension. In addition, LCB29 had a dual effect on strength--duration curves for mechanical threshold. It increased both the rheobasic potential and the steepness of the curve. It is concluded that LCB29 exerts a direct myorelaxant effect on rat soleus muscle; two sites of action are probably involved.     

The effect of cortisol on the excitability of the rat muscle fibre membrane and neuromuscular transmission.

The present experiments show that cortisol when applied in vitro, exerted two different effects on the electrical excitability of the diaphragm muscle fibre membrane and on the neuromuscular transmission depending on the concentration used. At low concentrations (2.5X10(-6) mol.l-1) it potentiated action potentials, increased resting membrane polarization by 3--4 mV and did not affect neuromuscular transmission. Higher concentrations (10(-2) mol.l-1) suppressed the action potential to a certain extent, depolarized the muscle fibre membrane by 6 mV and reduced the amplitudes of m.e.p.p.s and e.p.p.s as well as those of iontophoretically evoked acetylcholine potentials. It was concluded that the effect of low concentrations of cortisol is primary and is probably due to the enhancement of resting membrane permeability for K+ ions and to the changes in ion channels. Cortisol in high doses increased muscle oxygen consumption, so that its suppressing effect might be due to inhibition of energy metabolism.     

Chromium-associated 32P-labeling of proteins

The incubation of proteins with chromium (Cr3+ or Cr6+) in the presence of 32P ([gamma-32P]ATP or H3(32)PO4) at room temperature for 10-30 min resulted in the labeling of these proteins with 32P. The 32P-labeled proteins could be separated by SDS-polyacrylamide gel electrophoresis and identified by exposure to X-ray film. The characteristics of this procedure included: the optimal chromium concentration was 100 microM; the minimum requirement of each protein was 1 microgram; the optimal pH value was between 6 and 8; metal ions such as V5+, Mn2+ and Fe3+ strongly inhibited the effect of chromium, whereas Ca2+ and Mg2+ had little effect. It was concluded that chromium binds to the proteins and forms a complex with 32P to achieve the 32P-labeling of the proteins. This technique can be applied for the rapid preparation of 32P labels on protein markers for gel electrophoresis and for the identification of unknown protein species.     

Effect of ethmozine on action potentials and myocardial contraction in guinea pigs

Ethmozine decreased the maximum rate of action potential rise (Vmax) in a dose-dependent manner. Using the Scatchard plot the apparent dissociation constant was calculated to be 1.52 X 10(-5) g/ml. Ethmozine also decreased the force of contraction in the concentration range between 1 X 10(-6) and 1 X 10(-4) g/ml with the apparent dissociation constant obtained from the Scatchard plot being equal to 1.48 X 10(-5) g/ml. The linear correlation coefficient between the decrease in Vmax and the decrease in the force of contraction was found to be equal to 0.998. Negative inotropic action of ethmozine was less pronounced when the stimulation frequency had been switched from 0.8 to 0.1 Hz. The decrease in Vmax under the action of ethmozine (3 X 10(-5) g/ml) was diminished from 56 +/- 7% (0.8 Hz) to only 3 +/- 8% (0.1 Hz). This was accompanied by the decrease in the negative inotropic effect: from 58 +/- 9% (0.8 Hz) to 16 +/- 15% (0.1 Hz). It was assumed that the negative inotropic action of ethmozine was mediated by the Na--Ca exchange, which was inhibited by the decrease of the intracellular Na+ concentration due to the blockade of sodium channels by ethmozine.     

Effect of primycin on some electric properties of the frog skeletal muscle

The effect of primycin, a guanidine-type antibiotic was studied on the electric properties and 42K+ uptake of the frog sartorius and semitendinosus muscle. Both in normal and choline chloride Ringer solution, primycin evoked a concentration and time dependent depolarization of the surface membrane of the muscle. This depolarization was significantly increased by Na ions. Primycin treatment was shown to evoke a dose-dependent decrease of the depolarization induced by 20 mM K+-Ringer. When the muscles were incubated in a Ringer solution containing choline chloride, during an incubation period of 30 min the uptake of 42K+ was decreased to 12% upon the exposure to 5 x 10(-6) mol primycin as compared to the control value. As the primycin-induced depolarization increased, the shape and amplitude of the action potentials elicited by square-wave electric impulses were altered and decreased, respectively. In sodium isaethionate Ringer 1--2 x 10(-6) M primycin induced a slow depolarization resulting in firing potentials. The results suggest that primycin depolarizes the surface membrane exclusively through the blockade of the resting K+ channels, the other phenomena being the results of this depolarizing effect.     

Metal tolerance and biosorption potential of filamentous fungi isolated from metal contaminated agricultural soil

Heavy metal analysis of agricultural field soil receiving long-term (>20 years) application of municipal and industrial wastewater showed two- to five-fold accumulation of certain heavy metals as compared to untreated soil. Metal-resistant fungi isolated from wastewater-treated soil belonged to genera Aspergillus, Penicillium, Alternaria, Geotrichum, Fusarium, Rhizopus, Monilia and Trichoderma. Minimum inhibitory concentrations (MIC) for Cd, Ni, Cr, Cu, and Co were determined. The MIC ranged from 0.2 to 5 mg ml(-1) for Cd, followed by Ni (0.1-4 mg ml(-1)), Cr (0.3-7 mg ml(-1)), Cu (0.6-9 mg ml(-1)) and for Co (0.1-5 mg ml(-1)) depending on the isolate. Aspergillus and Rhizopus isolates were tested for their metal biosorption potential for Cr and Cd in vitro. Biosorption experiments were conducted with initial metal concentrations of 2, 4, 6 and 8 mM with a contact time of 4 h and wet fungal biomass (1-5 g) at 25 degrees C. Maximum biosorption of Cr and Cd ions was found at 6 mM initial metal concentration. Aspergillus sp.1 accumulated 1.20 mg of Cr and 2.72 mg of Cd per gram of biomass. Accumulation of these two metals by very tolerant Aspergillus sp.2 isolate was at par with relatively less tolerant Aspergillus sp.1 isolate. Rhizopus sp. accumulated 4.33 mg of Cr and 2.72 mg of Cd per g of biomass. The findings indicated promising biosorption of cadmium and chromium by the Rhizopus and Aspergillus spp. from aqueous solution. There is little, if any, correlation between metal tolerance and biosorption properties of the test fungi.     

Effect of chromium (III) ions and a cysteine complex of it on lipid bilayer membranes]

The interaction of Cr3+ ions and its cysteine complex with bilayer phospholipid membranes was investigated. It was found that chromium ions and the complex compound are adsorbed on the bilayer lipid membrane surface, changing the intramembrane potential difference. As pH increases, the adsorption of Cr3+ decreases and that of the complex rises. The adsorption of the complex leads to an increase in the rigidity of bilayer lipid membrane, which is not observed with chromium ions.     

Effects of dried bonito (katsuobushi) and captopril, an angiotensin I-converting enzyme inhibitor, on rat isolated aorta: a possible mechanism of antihypertensive action

In order to elucidate the mechanism of the antihypertensive action of dried bonito (katsuobushi), we compared the effects of dried bonito extracts with those of captopril, an angiotensin I-converting enzyme (ACE) inhibitor, on aorta preparations isolated from rats. Dried bonito extracts (3 x 10(-4) to 3 x 10(-3) g/ml) more potently relaxed contractions induced by norepinephrine (10(-7) M) than contractions induced by KCl (55.9 mM). Dried bonito extracts (3 x 10(-3) g/ml) slightly inhibited 10(-7) M angiotensin I-induced contractions. In contrast, captopril (10(-8) to 10(-7) M) did not affect 10(-7) M norepinephrine- or 55.9 mM KCl-induced contractions, but a higher concentration of captopril (10(-6) M) very slightly relaxed it. Captopril (10(-8) to 10(-6) M) markedly inhibited 10(-7) M angiotensin I-induced contractions in a concentration-dependent manner. These results suggest that antihypertensive mechanism of action induced by dried bonito involves direct action on vascular smooth muscle in addition to ACE-inhibitory activity.     

Chromium(III)-mediated structural modification of glycoprotein: impact of the ligand and the oxidants

The interaction of three types of chromium(III) complexes, [Cr(salen) (H2O2]+, [Cr(en)3]3+, and [Cr(EDTA) (H2O)]- with AGP has been investigated. [Cr(salen) (H2O2]+, [Cr(en)3]3+ and [Cr(EDTA) (H2O]- bind to Human alpha1-acid glycoprotein with a protein:metal ratio of 1:8, 1:6, and 1:4, respectively. The binding constant, K(b) was estimated to be 1.37 +/- 0.12 x 10(5) M(-1), 1.089 +/- 0.05 x 10(5) M(-1) and 5.3 +/- 0.05 x 10(4) M(-1) for [Cr(salen) (H2O2]+, [Cr(en)3]3+, and [Cr(EDTA) (H2O)]-, respectively. [Cr(en)3]3+ has been found to induce structural transition of AGP from the native twisted beta sheet to a more compact alpha-helix. The complexes, [Cr(salen) (H2O2]+ and [Cr(EDTA) (H2O]-, in the presence of H2O2, have been found to bring about nonspecific cleavage of AGP, whereas [Cr(en)3]3+ does not bring about any protein damage. Treatment of [Cr(salen) (H2O)2]+-protein adduct with iodosyl benzene on the other hand led to site specific cleavage of the protein. These results clearly demonstrate that protein damage brought about by chromium(III) complexes depends on the nature of the coordinated ligand, nature of the metal complex, and the nature of the oxidant.     

Interaction of DNA with divalent metal ions

The interaction between the native DNA macromolecules and Ca2+, Mn2+, Cu2+ ions in solutions of low ionic strength (10(-3) M Na+) is studied using the methods of differential UV spectroscopy and CD spectroscopy. It is shown that the transition metal ions Mn2+ exercise binding to the nitrogen bases of DNA at concentrations approximately 5 x 10(-6) M and form chelates with guanine of N7-Me(2+)-O6 type. Only at high concentrations in solution (5 x 10(-3) M) do Ca2+ ions interact with the nitrogen bases of native DNA. In the process of binding to Ca2+ and Mn2+ the DNA conformation experiences some changes under which the secondary structure of the biopolymer is within the B-form family. The DNA transition to the new conformation is revealed by its binding to Cu2+ ions.     

Action of cyclic nucleotide phosphodiesterase inhibitors on the acetylcholine potential

A study was made of the action of theophylline, isobutyrylmethylxanthine and caffeine on the sensitivity of mouse diaphragmatic muscle fibers to iontophoretically applied acetylcholine (ACh). It was shown that these substances at concentrations of 5 X 10(-4) -5 X 10(-3) M reduced the amplitude and increased the duration of the ACh potential as well as accelerated desensitization of the cholinoceptor at repetitive application of ACh. As regards the action on the ACh potential amplitude two phases which differed in the time-course of development and washing were recognized: rapid and slow. Addition of dibutyryl-cAMP (5 X 10(-4) M) after theophylline (10(-3) M) potentiated the latter's action on the ACh potential amplitude but did not influence its duration and the rate of desensitization. It is assumed that the action of phosphodiesterase inhibitors on the duration of the ACh potential and the rate of desensitization is not mediated by an elevation in the muscle cAMP content. Apparently, cAMP accumulation may be responsible but for the phase of a slow decrease in the ACh potential amplitude.     

Chromium(VI) bioaccumulation capacities of adapted mixed cultures isolated from industrial saline wastewaters

Enrichment mixed cultures tolerating relatively high concentrations of chromium and salt ions were isolated and their bioaccumulation properties improved by adaptation. Mixed cultures were enriched in Nutrient Broth media containing 25-300 mg l(-1) Cr(VI) and 0%, 2%, 4%, 6% (w/v) NaCl. Bioaccumulation of Cr(VI) was studied in a batch system as a function of initial pH (7, 8 and 9), Cr(VI) and NaCl concentrations. Increasing NaCl and Cr(VI) concentrations led to significant decreases in percentage uptake and dried weight of mixed cultures but increased maximum specific chromium uptake. The maximum specific chromium uptake value at pH 8 was 58.9 mg g(-1) for 316.1 mg l(-1) Cr(VI) in the absence of NaCl, while at pH 9 it was 130.1 mg g(-1) in media including 194.5 mg l(-1) Cr(VI) and 2% NaCl concentrations. At 4% NaCl, the maximum Cr(VI) uptake of 127.0 mg g(-1) for 221.1 mg l(-1) Cr(VI) occurred at pH 9, while at 6% NaCl the maximum Cr(VI) uptake of 114.9 mg g(-1) for 278.1 mg l(-1) Cr(VI) was found at pH 7.     

Opposite actions of caffeine and creatine on muscle relaxation time in humans.

The effect of creatine and caffeine supplementation on muscle torque generation and relaxation was investigated in healthy male volunteers. Maximal torque (T(max)), contraction time (CT) from 0.25 to 0.75 of T(max), and relaxation time (RT) from 0.75 to 0.25 of T(max) were measured during an exercise test consisting of 30 intermittent contractions of musculus quadriceps (2 s stimulation, 2 s rest) that were induced by electrical stimulation. According to a double-blind randomized crossover design, subjects (n = 10) performed the exercise test before (pretest) and after (posttest) creatine supplementation (Cr, 4 x 5 g/day, 4 days), short-term caffeine intake (Caf, 5 mg x kg(-1) x day(-1), 3 days), creatine supplementation + short-term caffeine intake (Cr+Caf), acute caffeine intake (ACaf, 5 mg/kg) or placebo. Compared with placebo, Cr shortened RT by approximately 5% (P < 0.05). Conversely, Caf increased RT (+ approximately 10%, P < 0.05), in particular as RT increased because of fatigue. RT was not significantly changed by either Cr+Caf or ACaf. T(max) and CT were similar during all experimental conditions. Initial T(max) was approximately 20% of voluntary maximal isometric contraction force, which was not different between treatments. It is concluded that Caf intake (3 days) prolongs muscle RT and by this action overrides the shortening of RT due to creatine supplementation.     

Heavy metal resistant freshwater ciliate, Euplotes mutabilis, isolated from industrial effluents has potential to decontaminate wastewater of toxic metals

The ciliate, Euplotes mutabilis, isolated from industrial wastewater of tanneries of Kasur, Pakistan, showed tolerance against Cd2+ (22 microg ml(-1)), Cr6+ (60 microg ml(-1)), Pb2+ (75 microg ml(-1)) and Cu2+ (22 microg ml(-1)). The heavy metals, Cr and Pb, were randomly selected for determining the capability of the ciliate to reduce the concentration of these metal ions in the medium and to evaluate its potential use as bioremediator of wastewater. The live protozoans could remove 97% of Pb2+ and 98% of Cr6+ from the medium, 96 h after inoculation of the medium containing 10 micro gml(-1) of metal ions. The acid digestion of ciliate showed 89% of Pb2+ and 93% of Cr6+ ions accumulated in the organism. When the ciliate was exposed to heavy metals at a larger scale viz., 10 l of water containing 10 micro gml(-1) of heavy metals, it removed 86% of Pb2+ and 90% of Cr6+ from the medium. The metal uptake ability of E. mutabilis, as evidenced by its survival and growth in 100ml and 10 l of water containing 10 microg ml(-1) of metal ions, reduction in the concentration of heavy metals in the medium and its increased uptake by the live cells, and no metal uptake by the heat killed ciliate can be exploited for metal detoxification of industrial wastes and environmental clean-up operations.     

心肌α1—肾上腺素受体激动对豚鼠心室乳头肌的影响

The alpha-adrenoceptor agonist phenylephrine (5.0 x 10(-6) mol/L) was used to stimulate myocardial alpha-adrenoceptors of the guinea-pig ventricular papillary muscle, and changes of transmembrane action potential and contractile force of the muscle were observed. The alpha 1-adrenoceptor blocker prazosin (5.0 x 10(-7) mol/L) and the alpha 2-adrenoceptor blocker yohimbine (5.0 x 10(-7) mol/L) were used to determine which subtype of alpha-adrenoceptor is responsible for the effects. The beta-adrenoceptor blocker propranolol (1.0 x 10(-6) mol/L) was used throughout the experiment. The results show that the myocardial alpha 1-adrenoceptor stimulation (1) increases the contractile force of the guinea-pig ventricular papillary muscle, (2) prolongs the time to peak contractile force while the duration of relaxation is not altered, (3) prolongs the fast response action potential duration, and (4) increases the maximal rate of depolarization during the phase 0 of the slow response action potential. It is suggested that the electrophysiological and positive inotropic effects of myocardial alpha 1-adrenoceptor stimulation might be due to the activation of the slow inward current and an increase in Ca2+ influx.     

Inhibitor effect of omeprazole in isolated human myometrial smooth muscle.

The aim of the present study was to investigate the effect of omeprazole, an H+-K+-ATPase inhibitor, in myometrial smooth muscle strips from women undergoing elective caesarean section at term. Isolated myometrial strips taken with informed consent were obtained from eight pregnant women undergoing elective caesarean section at term (not in labour) and mounted in organ baths for recording of isometric tension. We recorded the effect of increasing concentrations of omeprazole on spontaneous and Ca2+-induced contractions of myometrial smooth muscle and on contractions of myometrial smooth muscle pretreated with indomethacin (3 x 10(-6) M) and L-NAME (3 x 10(-5) M). Omeprazole (10(-4)-10(-3) M) decreased the amplitude and frequency of spontaneous contractions in a time- and concentration-dependent manner in all myometrial smooth muscle isolated from pregnant women. The decrease in amplitude of contractions in myometrial smooth muscle reached statistical significance beginning from the concentration of 3 x 10(-4) M. Addition of indomethacin (3 x 10(-6) M) and L-NAME (3 x 10(-5) M) in to the organ baths 30 min before did not change relaxation responses to omeprazole. When 8 mM Ca2+-precontracted in Ca2+-free medium myometrial smooth muscle were exposed to increasing concentrations of omeprazole (10(-5)-10(-3) M), omeprazole produced relaxation responses in a time- and concentration-dependent manner, reaching statistical significance at 10(-4) M. These results show: (1) omeprazole time- and concentration-dependently decreased spontaneous contractile activity in myometrial smooth muscle isolated from pregnant women, (2) omeprazole-induced relaxations was not influenced by indomethacin and N(G)-nitro-L-arginine methyl ester (L-NAME), suggesting that it is not mediated by cyclooxygenase products and nitric oxide, and (3) omeprazole brought about time- and concentration-dependently relaxation of myometrial smooth muscle precontracted by 8 mM Ca2+ in Ca2+-free medium. This effect of omeprazole may be due to blockade of the calcium channels.