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PubMed1991

Volume effects of starch-water interactions.

Volume changes arising from the sorption of water by three starches have been determined by dilatometry. By a recently described method, parameters of the G.A.B. equation have been used to resolve the volume changes into contributions from strongly sorbed water molecules in contact with the surface and from weakly sorbed water molecules in the remaining water layers. The latter produced only small volume effects. In contrast, the contact sorption caused very large volume decreases. Changes in these decreases with changing water content indicated two types of sorption sites, possibly crystalline and amorphous. In the case of waxy maize starch, for which literature data concerning its degree of crystallinity were available, the contact sorption could be quantitatively resolved into contributions from the presumably crystalline and amorphous portions, with the former exhibiting both higher affinity and larger volume changes for water molecules than the latter.

Chemical Phenomena↗
PubMed1995

Import of a new chloroplast inner envelope protein is greatly stimulated by potassium phosphate.

A cDNA clone encoding a major chloroplast inner envelope membrane protein of 96 kDa (IEP96) was isolated and characterized. The protein is synthesized as a larger-molecular-weight precursor (pIEP96) which contains a cleavable N-terminal transit sequence of 50 amino acids. The transit peptide exhibits typical stromal targeting information. It is cleaved in vitro by the stromal processing peptidase, though the mature protein is clearly localized in the inner envelope membrane. Translocation of pIEP96 into chloroplasts is greatly stimulated in the presence of 80 mM potassium phosphate which results in an import efficiency of about 90%. This effect is specific for potassium and phosphate, but cannot be ascribed to a membrane potential across the inner envelope membrane. Protein sequence analysis reveals five stretches of repeats of 26 amino acids in length. The N-terminal 300 amino acids are 45% identical (76% similarity) to the 35 kDa alpha-subunit of acetyl-CoA carboxyl-transferase from Escherichia coli. The C-terminal 500 amino acids share significant similarity (69%) with USOI, a component of the cytoskeleton in yeast.

Amino Acid Sequence↗
PubMed1992

Systemic administration of baclofen and the GABAB antagonist, CGP 35348, does not affect GABA, glutamate or aspartate in microdialysates of the striatum of conscious rats.

Previous in vitro experiments have shown that the GABAB agonist, baclofen, and the antagonist, CGP 35348, respectively, decrease and increase the autoreceptor-mediated release of GABA in brain slices and synaptosomes. Since it is not clear whether these autoreceptors are operative in vivo, an attempt was made to reproduce these results in brain dialysis experiments, knowing that only positive results would permit a conclusion in view of the doubts expressed in the literature with respect to the origin of extracellular GABA. Because of older reports of an inhibitory action of baclofen on the in vitro release of glutamate, which might be ascribed to the action of presynaptic GABAB heteroreceptors, extracellular glutamate and aspartate were also measured. Neither (-)-baclofen, administered systemically at a dose of 20 mg/kg i.p., nor the GABAB antagonist, CGP 35348 (300 mg/kg i.p.) had significant effects on basal overflow of GABA, glutamate, or aspartate nor on that evoked by 100 mmol/l K+ in the striatum of the conscious, freely moving rat. To ascertain this result, (-)-baclofen was also administered between two K+ stimulations, so that the first stimulation could serve as an intraindividual control of the second. The compound did not significantly affect K+ evoked overflow of any of the three transmitter amino acids under these conditions. It must be emphasized that these data do not exclude the operativity of presynaptic GABAB auto- and heteroreceptors in vivo. They only suggest that this question must, in all probability, be addressed by other techniques than brain dialysis.

Animals↗
PubMed1994

Effects of the bradycardic agent ZD 7288 on membrane voltage and pacemaker current in sheep cardiac Purkinje fibres.

The bradycardic mechanism of ZD 7288 (4-(N-ethyl-N-phenylamino)-1,2-dimethyl-6-(methylamino)pyrimidinium++ + chloride) was investigated in sheep cardiac Purkinje fibres. The pacemaker i(f)-current measured with the two-microelectrode voltage-clamp technique, as well as the diastolic depolarization rate and the frequency of spontaneously active fibres were evaluated. ZD 7288 did inhibit i(f)-current. The i(f)-amplitude recorded with a 0.8s-lasting test pulse from about -50 mV to -100 mV was reduced to 50% of control at 0.85 mumol/l and to 5% of control at 10 mumol/l. The threshold potential of i(f)-activation was unaffected at a concentration of 1 mumol/l ZD 7288. The time constant of i(f)-activation at different test potentials was not changed by 1 mumol/l ZD 7288. The drug was equally effective during i(f)-activation with a 0.5 s-lasting test pulse applied at 0.05 Hz or 0.5 Hz. During long lasting (5 s) hyperpolarizing test pulses (-120 mV) the inhibition of i(f)-current was removed. In constantly stimulated Purkinje fibres (0.5 Hz) the slope of the early diastolic depolarization was decreased by ZD 7288. The half-maximal effect occurred at 0.92 mumol/l. There was strong correlation over the concentration range of 0.01 to 10 mumol/l ZD 7288 between the decrease of the slope of early diastolic depolarization and inhibition of i(f)-amplitude recorded with 0.8s-lasting test pulses to -100 mV. The correlation coefficient was r = 0.97. These results will explain the decrease in frequency of spontaneously active (about 0.6 Hz) Purkinje fibres.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1993

Purification of fusion proteins using affinity microspheres in aqueous two-phase systems.

Affinity microspheres were prepared by immobilizing human gamma-globulin (H gamma Gb) onto carboxylated poly (styrene/acrylamide) latex particles [P(St/AAm)-H; average diameter 0.33 microns], which were prepared by emulsifier-free emulsion polymerization. H gamma GB was covalently immobilized onto the latex particles with high efficiency by the carbodiimide method. A fusion protein (ZZB1B2) of immunoglobulin G and albumin-binding domains (ZZ and B1B2, respectively) was expressed intracellularly and extracellularly in Escherichia coli and was purified by the affinity microspheres. In poly (ethylene glycol) (PEG)/potassium phosphate aqueous two-phase system, the affinity microspheres were partitioned into the PEG-rich top phase, while cells and cell debris of E. coli were displaced into the salt-rich bottom phase. Therefore, ZZB1B2 was directly purified from cell disintegrate or culture broth by combining the affinity microspheres with the aqueous two-phase partitioning, and its purity was almost the same as that purified by conventional affinity chromatography. Therefore, by this purification method, the primary purification process and the subsequent high resolution purification process are combined, and the number of purification steps can be reduced.

Chromatography, Affinity↗
PubMed1996

Combined effects of acute lead acetate exposure and tone exposure of the guinea pig cochlea.

Lead acetate exposure to humans can induce various disorders of the cranial nerves. Although vertigo and sensorineural deafness have been reported in lead workers, the dose effects of lead acetate on the cochlea and eighth cranial nerve are not well documented. We investigated the effects of lead acetate on the male albino Hartley guinea pig cochlea by measuring cochlear microphonics (CM), whole nerve action potential (AP), endocochlear potential (EP) and K+ ion concentration of the endolymph. Animals were given lead acetate by intraperitoneal injection as 20 mg/week for 4 consecutive weeks. A total dose < 80 mg did not induce electrophysiological changes in the cochlea. However, the AP output voltage (N1) decreased if the 80 mg lead acetate treatment was followed by an 80 dB tone exposure at 6 kHz during 24 h. A change was observed in CM and EP but not K+ ion concentration in the scala media.

Action Potentials↗
PubMed1992

Renal potassium bicarbonate release in humans exposed to an acute volume load.

Cells of the renal medulla regulate their volume by transmembrane ion movements when exposed to large changes in osmolality. Since renal cells in culture release KHCO3 in response to hypotonic stress [11], we investigated the effect of an acute water load on urinary KHCO3 excretion in 5 healthy individuals. Water diuresis was induced by the ingestion of 1.5 l hypoosmolal fluid (22 mosm/kg H2O) over 15 min. The rate of urinary volume excretion increased from an initial value of 1.4 ml/min to 9.3 ml/min after 75 min. Urinary osmolality dropped from an initial value of 940 +/- 32 mosm/kg H2O to 74 +/- 4 mosm/kg H2O (n = 5). The decrease of osmolality was accompanied by the transient release of potassium and bicarbonate. Peak values of KHCO3 excretion were observed between 30 and 45 min after the onset of the experiment corresponding to the drop of urinary osmolality. The magnitude of renal potassium release correlated significantly (r = 0.93; P less than 0.05) with endogenous plasma aldosterone concentrations measured prior to the experiment in the 5 volunteers. We conclude that medullary epithelial cells release KHCO3 when exposed to hypotonic stress. The volume regulatory response is upregulated by aldosterone.

Adult↗
PubMed1996

A pharmacokinetic and pharmacodynamic evaluation of buffered sublingual captopril in patients with congestive heart failure.

OBJECTIVE: The pharmacokinetics and pharmacodynamics of buffered sublingual captopril were assessed in patients with congestive heart failure (CHF). METHODS: The study was carried out in a randomised single-blind cross-over fashion (n = 6, 4 males and 2 females) and involved two study days, at least 7 days apart. Baseline measurements were carried out for plasma renin activity (PRA), blood pressure (B.P.) and heart rate (H.R.). Captopril (12.5 mg) was administered sublingually with dibasic potassium phosphate which maintained salivary pH at 7, or perorally with 100 ml of water. Further B.P., H.R. measurements and venous blood samples were taken over a 3 hour period post-drug administration. Blood samples were analysed for captopril and PRA levels. RESULTS: tmax after buffered sublingual administration of captopril, which ranged from 40-60 min (median = 40 min), was significantly shorter than after peroral administration (range 60-120 min, median = 90 min). Cmax was slightly greater after buffered sublingual than after peroral administration with mean values of 108.2 vs. 94.0 ng.ml-1. AUC values were similar after both routes of administration. Systolic and diastolic B.P. vs. time profiles for each administration method were significantly different i.e. sublingual administration produced an earlier reduction in B.P., however, HR did not differ significantly between the two routes. CONCLUSION: The data indicate that this novel administration method of captopril leads to an increased rate, but an unchanged extent of captopril absorption, suggesting a modest therapeutic advantage with the use of buffered sublingual captopril if a rapid reduction in blood pressure is required.

Administration, Sublingual↗
PubMed1989

Effect of phosphate on oxygen-hemoglobin affinity, diphosphoglycerate and blood gases during recovery from diabetic ketoacidosis.

The effects of intravenous phosphate administration on the hemoglobin-oxygen affinity, the 2,3 diphosphoglycerate level and blood gases were investigated in twenty severe diabetic patients with ketoacidosis in the intensive care unit. Ten received phosphate (mean total amount for each patient = 300 mEq) and the others did not. The only significant difference noted in all indices measured during the recovery period of eight days was seen to occur after 48 h; the P50 in vivo (Torr) was slightly higher in the group who received phosphate (22.5 +/- 1.6 vs 20.5 +/- 2.2) and for the Hill coefficient (2.4 +/- 0.2 vs 2.2 +/- 0.1). This drop in the oxygen affinity of hemoglobin may be useful in subjects at risk of hypoxia, for example those with cardiac or respiratory failure and justifies the use of phosphate in the first 48 h of treatment of patients with diabetic ketoacidosis.

Adult↗
PubMed1985

Chelation in metal intoxication XVII: Antidotal efficacy of polyaminocarboxylic acids on acute chromate toxicity.

Some polyaminocarboxylic acids containing amino and carboxyl groups as metal binding sites in different structural arrangements were evaluated for their relative efficacy in protecting against acute chromate intoxication in mice. Nitrilotriacetic acid (NTA) and 1,2 cyclohexylenediamine tetraacetic acid (CDTA) were most effective in preventing mortality (50-70%) due to a lethal dose of potassium chromate at one-tenth of their respective LD50.

Amino Acids↗
PubMed1993

The effect of supplementing hypothermic crystalloid cardioplegia with catalase plus allopurinol in the isolated rabbit heart.

The effect of adding allopurinol and catalase to hypothermic cardioplegia for ischemic-reperfusion injury was investigated in the isolated rabbit heart. Hearts were divided into two groups, namely: Group C (n = 7), which received a hypothermic crystalloid cardioplegic solution alone (4 degrees C), and group T (n = 7), which received the hypothermic cardioplegic solution with allopurinol (148 mumol/L)13 and catalase (37 nmol/L).12 The cardioplegic solution was infused continuously into the isolated hearts, which had been placed in ice-cold saline, during a 12 h preservation. Subsequently, the hearts were mounted on a noncirculating, nonpulsatile perfusion circuit using Krebs-Henseleit buffer solution at 37 degrees C for 1 h at a constant perfusion pressure of 75 mm Hg. The left ventricular developed pressure (LVDP), maximum rate of pressure change (max dp/dt), and percent recovery of coronary flow were higher, while the creatine phosphokinase concentration and left ventricular end diastolic pressure (LVEDP) were lower in group T. The tissue malondialdehyde concentration and water content were similar in both groups. Thus, cardiac function after a 12 h preservation was enhanced by the added combination of allopurinol and catalase to the cardioplegic solution, supporting its role in the prevention of free radical reperfusion injury in cardiac preservation.

Allopurinol↗
PubMed1984

The action of thallium acetate on spontaneous transmitter release in the rat neuromuscular junction.

Frequencies and amplitudes of miniature endplate potentials (MEPP's) were recorded from neuromuscular junctions of the rat phrenic nerve-diaphragm preparation in vitro. Superfusion of the preparations with Ringer solution containing thallium acetate (Tlac) gradually increased the frequency of MEPP's by a factor of 10 within 30 min (1 X 10(-3) mol/l Tlac) and 180 min (5 X 10(-4) mol/l Tlac), whereas the amplitude of MEPP's remained unchanged. Frequency of MEPP's fitted a Poisson-distribution which persisted during superfusion with Tl+-Ringer. Sub-MEPP amplitudes remained unaffected by the action of thallium. It is concluded that thallium interferes presynaptically with spontaneous transmitter release.

Action Potentials↗
PubMed1995

Early reaction type allergies and diseases of the respiratory passages in employees from persulphate production.

The prevalence of positive skin-prick test reactions ammonium persulphate and potassium persulphate (1% and 5% solutions) was tested in a cross-sectional study on 52 employees of a company producing persulphates after a case of "persulphate asthma" was observed. A random test of 13 persons without occupational exposure to persulphates served as controls; among them all the skin-prick test reactions were negative. Eight company employees showed a positive skin-prick test reaction to at least one of the persulphate solutions tested. Employees showed lower lung function results with a positive prick test reaction than did employees with a negative result. The positive skin-prick reactions correspond well to the anamnestic data and indicate a possible relationship to obstructive ventilation disorders. The results therefore suggest an IgE-induced, allergic pathomechanism of "persulphate asthma" triggered by persulphates.

Adult↗