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B Pohl

Publications and source records attributed to B Pohl.

36 records · Page 2Linked to original sources
PubMed1992

Modulation of calcium current gating in frog skeletal muscle by conditioning depolarization.

1. Ca2+ inward currents were measured by voltage clamping cut skeletal muscle fibres of the frog (Rana esculenta) in a double-Vaseline-gap system. 2. In order to study the basis of the previously described fast gating mode induced in the Ca2+ inward current by a conditioning depolarization we quantitatively analysed the response to differing features of the conditioning prepulse. 3. The faster activation seen during the second of two depolarizations was confined to the component of the inward current which could be blocked by 5 to 10 microM nifedipine. 4. By applying depolarizing conditioning pulses of gradually increasing length the time course of the transition to the fast gating mode could be determined. 5. Both the transition to the fast gating mode (point 4) caused by a depolarization and the slow inward current activated during the same depolarization showed similar voltage-dependent kinetics. 6. The kinetic change of the test current appeared to be equal when the same fractional activation was achieved at the end of the conditioning pulse independent of its duration or amplitude. 7. Flash photolysis of nifedipine in the interval between conditioning and test pulse showed that the predepolarization causes a rate-enhancing effect even though the slow channels were blocked by nifedipine during the conditioning pulse. 8. We conclude that the transition of the calcium channel from its slow to its fast gating mode is determined by the slow voltage-dependent reaction which limits the rate of channel opening under control conditions. This reaction is apparently not prevented by the binding of nifedipine and the block of current flow through the channel.

Animals↗
PubMed1990

Effects of gallopamil on calcium release and intramembrane charge movements in frog skeletal muscle fibres.

1. Intramembrane charge movements and changes in intracellular Ca2+ concentration were studied in voltage clamp experiments on cut twitch muscle fibres of the frog. The restoration from inactivation caused by steady depolarization and its modification by the phenylalkylamine Ca2+ channel antagonist gallopamil (D600, 10-30 microM) were investigated. 2. D600 prevented the restoration from inactivation of Ca2+ release which normally occurred at -80 mV. In D600 Ca2+ release recovered from inactivation at -120 mV. 3. D600 did not alter the characteristics of intramembrane charge movements in the depolarized fibre (charge 2) but the increase in the amount of mobile charge in the test voltage range above -60 mV, which normally occurs after changing the holding potential to -80 mV, was suppressed. The charge movement characteristics of D600-paralysed fibres, which were held at -80 mV, equalled those of normal depolarized and inactivated fibres. 4. Control records for the charge movement analysis were always obtained by voltage steps above 0 mV. Using the 'conventional' control in the potential range between -80 and -160 mV led to an underestimation and a kinetic deformation of charge movements in D600-treated fibres, which was due to various amounts of nonlinear charge in the control. 5. Like the restoration of Ca2+ release at -80 mV in normal fibres the recovery from paralysis at -120 mV in D600-treated fibres was accompanied by a significant increase in mobile charge in the potential range positive of -60 mV. Both Ca2+ release and charge movement at test potentials above -60 mV recovered with almost identical time course. 6. Restoration of Ca2+ release at a holding potential of -80 mV in normal fibres or at -120 mV in D600-treated fibres could not be clearly correlated to charge movement changes in the voltage range negative of -60 mV (charge 2). 7. Our results are consistent with a voltage-dependent inhibitory effect of D600 on the charge displacement that controls Ca2+ release from the sarcoplasmic reticulum but provide little evidence for a conversion of charge 2 into the charge that is involved in the control of Ca2+ release.

Action Potentials↗
PubMed1990

Fast gating kinetics of the slow Ca2+ current in cut skeletal muscle fibres of the frog.

1. Calcium currents and intramembrane charge movements were measured in cut twitch muscle fibres of the frog and the time course of activation of the current was studied using various conditioning pulse protocols. 2. When a conditioning activation was produced by a depolarizing pulse which ended before inactivation occurred, a subsequent depolarization led to a faster onset of activation, indicating that the system had not completely returned to the initial state during the interval between the two pulses. 3. The interval between conditioning and test pulse was varied at different subthreshold potentials to study the time course of restoring the steady-state conditions. Complete restoration required a waiting period of about 1 min at the holding potential of -80 mV due to a very slow process but partial recovery was reached within 100 ms. This initial recovery process was strongly voltage dependent and became considerably slower when the interval potential approached the threshold for current activation. 4. Stepping to a roughly 10 mV subthreshold potential without applying a conditioning activation caused no change in the time course of the current produced by a subsequent test depolarization. Depolarizing just to the current threshold caused a slowly progressing acceleration of test current activation. 5. The peak current-voltage relation in the fast gating regime caused by a conditioning activation coincided with the current-voltage relation measured under steady-state conditions, indicating not that a new channel population had become activated but that the same channels showed a different gating behaviour. 6. Intramembrane charge movements measured in 2 mM-Cd2+ and tested at potentials between -40 and +40 mV showed negligible changes when preceded by a strong depolarization. 7. We discuss several possible models which can explain the fact that the current is speeded up by a conditioning activation while the charge movements remain unchanged. It is possible that the fast voltage-dependent transition which becomes visible after conditioning pulses reflects a rapid conformational change of the Ca2+ channel molecule which also occurs during its normal gating mode but remains undetectable in terms of conductance. In view of the hypothesis that the Ca2+ channel molecule forms a voltage sensor for excitation-contraction coupling this fast transition could be coupled to the control of Ca2+ release from the sarcoplasmic reticulum.

Animals↗
PubMed1987

The nonenzymatic oxidation of glutathione in the presence of plasmalike concentrations of disulfides and copper ions.

The oxidation of glutathione catalyzed by a combination of low concentrations of disulfides and copper and iron ions (as they occur in the blood plasma) was investigated and compared with data obtained in vivo studies. At pH 7.4 and 37 degrees C oxidation of glutathione (3 mmol/L) in a solution saturated with oxygen could be induced from 0 to 3, 5, 10, and 21 nmol/min and mL by the addition of 0.1, 1.0, 10, and 100 mumol/L CuCl2, respectively. The presence of 50 mumol/L cystinylbisglycine as an additional component increased the rate of oxidation by a factor between two and three. Cystine was only about one third as active as cystinylbisglycine, and trans-4,5-dihydroxy-1,2-dithiane, the disulfide derivative of dithiothreitol, was even less effective in propagating glutathione oxidation. FeCl2 in combination with the disulfides was 30 times less active than copper as a catalyst. With plasmalike concentrations of the reactants, a rate of glutathione oxidation of 0.2 to 0.8 nmol/min and mL, depending on the availability of free plasma copper, could be approximated. This rate corresponds to 8% to 30% of total plasma glutathione oxidation.

Copper↗
PubMed1986

Studies on the reaction mechanism of general acyl-CoA dehydrogenase. Determination of selective isotope effects in the dehydrogenation of butyryl-CoA.

The kinetic properties of general acyl-CoA dehydrogenase from pig kidney have been investigated using normal butyryl-CoA as well as an alpha-deutero, beta-deutero- and perdeutero-butyryl-CoA. In turnover catalysis, isotope effects of 2, 3.6, and 9 were found respectively. In the reductive half reaction the isotope effects were 2.5, 14, and 28 for the same substrates, and 21 for (2R,3R)-(2,3-D2)butyryl-CoA. No intermediates are apparent during the reduction of oxidized enzyme to the presumed complex of reduced enzyme and crotonyl-CoA. The results are interpreted as indicating a high degree of concertedness during the rupture of the alpha and beta C-H bonds. They are compatible with a mechanism in which simultaneously the alpha-hydrogen is abstracted as a proton, while the beta-hydrogen is transferred to the oxidized flavin as a hydride.

Acyl Coenzyme A↗
PubMed1984

Partial purification and characterization of rabbit-kidney brush-border (Ca2+ or Mg2+)-dependent adenosine triphosphatase.

The ATPase activity of rabbit-kidney brush border can be activated almost equally well by Ca2+ and Mg2+ and, therefore, should be called (Ca2+ or Mg2+)-ATPase. This enzyme was solubilized and enriched 14-fold by the following steps: pretreatment with papain removed 69% of alkaline phosphatase without attacking a significant portion of the ATPase activity. Addition of 1% cholate removed 65% of the protein but no ATPase activity. The combination of cholate (0.5%) and deoxycholate (0.4%) solubilized most of the ATPase activity and most of the remaining protein. A column chromatography of the extract on Sepharose CL-2B resulted in an 6.5-fold increase of specific ATPase activity. A precipitation by ammonium sulfate (40% saturation) produced an additional 1.9-fold increase. The yield of this partial purification was 16%. Towards the nucleotides UTP and GTP the enzyme showed an activity slightly higher, and towards ITP and CTP an activity slightly lower than that with ATP. ADP was split about half as fast as ATP. AMP was not accepted by the enzyme. Replacing MgCl2 by CaCl2 resulted in an ATPase activity of 92% of that with MgCl2. Using calcium- and magnesium-ATP as substrates, apparent Km values of 0.22 and 0.33 mM, respectively, were obtained. The gel electrophoresis revealed the enrichment of a protein with an apparent Mr of 95000 and also that of microvillus actin.

Adenosine Triphosphatases↗
PubMed1984

The beta-receptor: isoproterenol anxiety states.

To learn the effect of isoproterenol on patients meeting Research Diagnostic Criteria (RDC) for panic disorder, we administered isoproterenol, racemic sodium lactate, and glucose to them and to nonpsychiatric control subjects. Each subject received all 3 infusions, double-blind in random order. A 21-item self-rating panic scale was constructed from the RDC for panic disorder and was used to identify RDC panic attacks. The results of this study and the preliminary results from the infusions after treatment with imipramine are discussed in the text, and the results from the first patient to be reinfused after treatment are presented graphically.

Adolescent↗
PubMed1983

Comparative studies of purified and reconstituted monoamine oxidase from bovine liver mitochondria.

Monoamine oxidase, a strictly membrane-bound flavoenzyme, has been purified using a modified procedure recently developed. Probably similarly to other preparations known from the literature, the enzyme solubilizes to a clear suspension, which represents large clusters ranging in size from 5 to 50 nm containing appreciable amounts of residual lipids. The purified and reconstituted enzymes are inhibited differently by deoxycholate. In contrast to deoxycholate, Triton X-100 does not inhibit the purified enzyme, but rather disintegrates the lipid-enzyme clusters to the smallest active units. However, removal of the detergent leads to reconglomeration to larger lipid-enzyme aggregates. Using the irreversible destruction of the enzyme by deoxycholate as assay, reconstitution of the enzyme with exogeneous lipids has been studied. All basic enzyme properties, such as stability, maximal activity (V), Michaelis constant (Km), pH- and temperature-dependence of the purified and reconstituted systems, are significantly different.

Animals↗
PubMed1978

The brush border of rabbit kidney, a cellular compartment free of glycolytic enzymes.

Activities of four enzymes of the glycolytic pathway, hexokinase, glyceraldehyde 3-phosphate dehydrogenase, pyruvate kinase and lactate dehydrogenase, were determined in a vesicular brush-border preparation from rabbit kidneys. The specific activities of the enzymes were decreased several-hundredfold in the brush-border preparation compared with a kidney homogenate, but the enzymes were not totally absent. Density-gradient centrifugation of the brush-border preparation yielded brush border of even higher purity and also a characteristic pattern of distribution for each of the contaminating intracellular membranes. The presence of hexokinase in the brush-border preparation could be traced to contaminating mitochondria, and that of glyceraldehyde 3-phosphate dehydrogenase, pyruvate kinase and lactate dehydrogenase to contaminating vesicles derived from the endoplasmic reticulum. The brush-border vesicles contained some ATP. An intravesicular concentration of 0.1mm was estimated, indicating that the vesicles had retained at least a part of their original content. Experiments in which fluorescein isothiocyanate-dextran (mol.wt. 20000) was present during cell lysis revealed that much, but not all, of the brush-border contents had been exchanged with the medium. The complete absence of glycolytic enzymes from brush-border vesicles, which had retained part of their original content, indicates that the brush border does not contain glycolytic enzymes in vivo and can be thought of as a compartment of its own, somehow separated from the cytoplasm.

Adenosine Triphosphate↗
PubMedDate not supplied

[Free amino acids in the saliva of children with phenylketonuria].

UNLABELLED: Free amino acids were determined quantitatively in saliva of 23 children with phenylketonuria (male = 11, female = 12) (ages 6-17 years). Saliva was deproteinised by adding an equal volume of 5% sulphosalicylic acid and the amino acids were separated by ion exchange column chromatography. RESULTS: The comparison of the amino acid concentrations in saliva of phenylketonuric children with healthy children (male = 34, female = 31) (ages 6-13 years) showed, that vast majority of amino acids - taurine, serine, glutamine, glycine, alanine, citrulline, a-aminobutyric acid, valine, isoleucine, leucine, tyrosine, phenylalanine, ornithine, lysine, delta-aminovaleric acid - were excreted significantly lower in saliva of phenylketonuric children.

Adolescent↗
PubMedDate not supplied

The quick machine--a mathematical model for the extrinsic activation of coagulation.

The present paper describes a mathematical model of the kinetics of the extrinsic coagulation cascade in vitro. The coagulation factors FI, FII, FV, FVII, FX, heparin and antithrombin III (ATIII) as well as soluble fibrin polymers are considered. The effect of single-factor deficiencies of the factors II, V, VII and X, diseases like hypo- and dysfibrinogenaemia, hepatic insufficiency, inhibited polymerisation by degradation products, heparin therapy with and without ATIII deficiency and coumarin therapy on prothrombin time can be portrayed. Physiology of coagulation is represented in a dynamic mathematical model as a differential equation system. The model is based on three reaction types: enzymatic cleavage, complex formation and polymerisation. The model was implemented in a continuous simulation program on a personal computer using the Pascal programming language. Unknown rate constants were estimated by chi 2 fit. Prothrombin time calculated by the model was compared to the training set of 20 plasma samples. In most but not all cases the model harmonized quite well with the coagulometric data.

Blood Coagulation↗