Biomedical subjects
K Mohr
Publications and source records attributed to K Mohr.
[Computer-assisted speech recognition and display of x-ray findings].
A voice recognition system, called Tangora, has been designed for the German language; its prototype has been tested to assess its clinical usefulness for radiological reporting. Its technical vocabulary consists of 20,000 words. The system recognises words spoken provided short pauses are inserted. The Tangora system was compared with conventional methods of dictation, using 68 radiological reports. The work necessary for each system was analysed. The average time taken by the Tangora system per report was 671 seconds compared with 182 seconds for conventional dictation but improvements in the speed of the new system for radiological reporting is to be expected.
Lack of inotropic effect of cyclosporin A in isolated guinea pig left atria.
OBJECTIVE: Cyclosporin A is being widely used to prevent graft rejection in organ transplantation and to treat autoimmune diseases. Since various toxic side effects have been observed, the aim of this study was to look for even a subtle deleterious effect of cyclosporin A on cardiac inotropy in electrically stimulated guinea pig left atria. METHODS: The left atrial muscles of guinea pigs, in Tyrode's solution containing 2.7 or 5.4 mM potassium, were electrically stimulated by one of two methods: (1) continuously at 3 Hz, during which cyclosporin A was applied cumulatively (from 10(-9) to 10(-5) M); or (2) stimulated intermittently at 2.5 Hz in 5 mM cyclosporin A, with rest periods of 4 s duration interposed every 4 min. The effects of cyclosporin A on contractile force were observed for 150 min in the first stimulation method, and the effects on the steady state contractile force and amplitude of post-rest contraction were observed for 240 min in the second method. RESULTS: The steady state contractile force of the atria declined within the 4 h period at 2.7 mM potassium in Tyrode's solution both in the cyclosporin A group (n = 10) and in the control group (n = 5) to 68(SD 11)% and to 63(4)%, respectively. After 4 h the amplitudes of the post-rest contraction were 101(16)% and 101(4)% in cyclosporin A and control groups, respectively. At 5.4 mM potassium, the following values were obtained (cyclosporin A v control): steady state force 70(8)% (n = 11) v 69(8)% (n = 5); post-rest force 105(9)% v 102(7)%. CONCLUSIONS: Cyclosporin A does not influence the steady state contractile force or the amplitude of the post-rest contraction, suggesting the absence of inotropic effects on isolated guinea pig left atria.
Enantioselectivity of asocainol studied at different conditions: a novel approach to check the feasibility of molecular models of antiarrhythmic drug action.
In terms of the "guarded receptor" hypothesis, changes in potency of Na+ channel blocking drugs reflect alterations in drug access to and/or egress from a compartment facing a binding site with constant affinity. Potency is therefore assumed to be determined by changes in drug diffusion, its mobility in the electric field, protonation etc. Hence, the potencies of enantiomers, i.e. compounds with identical physicochemical properties, should be influenced in a parallel manner by the condition. To test this prediction, actions of the enantiomers of the stereoselective antiarrhythmic drug asocainol were compared at various membrane potentials and stimulus frequencies. Several experimental models indicative of Na+ channel block were used: the elevation of the rectangular pulse stimulation threshold (RPT) and the suppression of alternating-current induced arrhythmia (ACT) were studied in guinea-pig atria. The reduction of the upstroke velocity of action potentials was measured in guinea-pig papillary muscles. The inhibition of whole-cell Na+ currents was investigated in isolated guinea-pig ventricular myocytes. In all these assays, (+)-asocainol was more potent than the (-)-enantiomer. Lowering the membrane potential and/or increasing the stimulus frequency enhanced the effects of both enantiomers. However, over a certain range of conditions, the potency of (+)-asocainol was more markedly affected than that of (-)-asocainol, indicating that the eudismic ratio between potencies of the two drugs is not constant. Accordingly, these findings are inconsistent with the guarded receptor hypothesis.
A method for simultaneous evaluation of drug-effects on excitability and inotropy in isolated cardiac preparations.
A method is described which allows determination of the threshold of excitability of electrically stimulated, regularly contracting isolated cardiac preparations. The force of the contraction (CF) is isometrically recorded and serves as feed-back signal indicating effective stimulation. The pulse intensity is decreased monoexponentially as long as contractions are elicited. If the mechanical response does not occur, the pulse intensity is immediately reset to the initial high value and the pulse is delivered with a latency of a few milliseconds. A stimulus intensity just below threshold is recorded as the rectangular pulse threshold (RPT). The method was applied in order to compare the effects of a number of antiarrhythmic drugs including the beta-blocker propranolol on the electrical excitability (1/RPT) and on the contractility of guinea pig left atria stimulated at 3 Hz. In general, the drugs depressed excitability and contractility concomitantly. The rank order of potency with respect to the reduction of excitability was: aprindine greater than propafenone greater than propranolol greater than quinidine greater than mexilitine greater than lidocaine. The Ca-antagonist verapamil reduced contractile force most powerful but had no effect on excitability. Presumably, RPT reflects sodium-channel function. In conclusion, the described method offers an easily operable test of drug effects on the excitability threshold and the contractility of isolated cardiac preparations.
Equipotent allosteric effect of W84 on [3H]NMS-binding to cardiac muscarinic receptors from guinea-pig, rat, and pig.
W84 (hexamethylene-bis-[dimethyl-(phthalimidopropyl)-ammonium bromide]) is an experimental antidote against organophosphorus poisoning and has been found to affect muscarinic cholinoceptors allosterically. The attempt was made to test whether the W84-action on muscarinic cholinoceptors depends on the species. For this purpose, the effect of W84 on the binding of [3H]N-methylscopolamine ([3H]NMS) was investigated in membrane-suspensions from the hearts of guinea pigs, rats, and pigs in 3 mM MgHPO4, 50 mM Tris, pH 7.3, at 23 degrees. W84 inhibited [3H]NMS-binding in the three membrane suspensions with similar potency (half-inhibitory concentration IC50: 2-5 microM). To evaluate the allosteric activity of W84, its effect on the dissociation of [3H]NMS was determined. At 3 microM, W84 diminished the rate of [3H]NMS-dissociation to about 20% of the control in three suspensions. At 100 microM of W84, [3H]NMS-dissociation was almost prevented. In conclusion, W84 acted equally on the cardiac cholinoceptors of guinea pigs, rats, and pigs, respectively. It can be anticipated that M2-cholinoceptors of other species would likewise be affected by W84.
C14-aminosteroid LNF 209, an agent with positive inotropic and antimuscarinic activity.
LNF 209 is a cardioactive steroid containing at position C14 a protonized amino group. It was tested whether LNF 209 has antimuscarinic properties besides its cardiotonic effect, which was also quantified. In guinea pig left atria (3 Hz, 0.9 mM Ca2+, 5.4 mM K+), LNF 209 increased the force of contraction at concentrations > or = 1 microM, thus having a tenfold lower potency than ouabain. Correspondingly, cardiac glycoside binding sites in guinea pig cardiac membranes labeled with [3H]ouabain were occupied by LNF 209 (Ki = 1.7 microM) at concentrations tenfold higher compared with ouabain (Kd = 0.14 microM). The negative inotropic effect of the muscarinic agonist oxotremorine was antagonized by LNF 209, but not by ouabain; in the Schild plot, the data for LNF 209 could be connected by a line with a slope of unity and a pA2 = 7.5. The binding of [3H]N-methylscopolamine ([3H]NMS) to the M2-cholinoceptors in guinea pig cardiac membranes was inhibited by LNF 209 with a Ki = 0.5 microM; LNF reduced the affinity of [3H]NMS binding without affecting the number of receptor sites. In isolated segments of guinea pig ileum, LNF 209 antagonized the effect of oxotremorine with a pA2 = 7.4. It is concluded that LNF 209 is a competitive antagonist at M-cholinoceptors without preference for the cardiac M2-cholinoceptors. Whether the antimuscarinic property is of significance in species highly sensitive to digitalis remains to be established.
The ability of cationic amphiphilic compounds to depress the transition temperature of dipalmitoylphosphatidic acid liposomes depends on the spatial arrangement of the lipophilic moiety.
The hypothesis was tested with the help of model compounds that the ability of cationic amphiphilic drugs to depress the phase-transition temperature Tt of dipalmitoylphosphatidic acid (DPPA) liposomes depends on the spatial arrangement of the lipophilic moiety. The main structure of the compounds with identical cationic side chain was 1-dimethylamino-3-phenylpropane (compound I). A further phenyl ring was introduced either at C3 of the propane chain (compound II) to broaden the lipophilic moiety, or in para-position of the phenyl ring (compound III) to elongate it. As shown by differential scanning calorimetry, the reduction of Tt (control 64 degrees) amounted for compound I to 29 degrees, for compound II to 28 degrees and for compound III to 53 degrees. In order to assess the binding affinity of the compounds to DPPA, their inhibitory effect on 45Ca(2+)-binding to DPPA films was measured. The IC50 values were 2100 microM for compound I, 40 microM for compound II, and 9 microM for compound III. Thus, binding affinity corresponded with the hydrophobicity of the compounds. In contrast, the depressing effect on the transition temperature was only augmented by the additional phenyl ring when substituted in the elongating position.
Diastolic tension and contraction amplitude in calcium-loaded rat ventricular myocardium are differently affected by drugs.
1. To obtain a measure of drug effects on myocardial function during diastole, the following experimental protocol was designed: rapid electrical stimulation (5 Hz) at high Ca02+ caused an elevated diastolic tension, which could be subjected to drug-induced alterations. 2. Antiarrhythmic drugs (quinidine, propafenone, procainamide, mexiletine) were able to lower diastolic force without appreciably decreasing contraction amplitude. Calcium antagonists (nifedipine, verapamil) lowered both parameters in parallel. 3. Veratridine and Bay K 8644 both enhanced diastolic tension, but only Bay K 8644 concomitantly elevated contraction amplitude. 4. These findings may be explained when taking into account differential actions of sodium- and calcium channel modulating drugs, respectively, on cellular Ca2+ movements. In quantitative terms, the non-linear dependence of myocardial force on Cai2+ also had to be considered.
The positive inotropic drugs DPI 201-106, BDF 9148, and veratridine increase ouabain toxicity and [3H]ouabain binding in guinea pig heart.
The interaction of three positive inotropic compounds, which are modulators of sodium channels, with the cardiac glycoside ouabain was investigated in isolated guinea pig atria. In the presence of DPI 201-106 (3 x 10(-7) M), of its new acetidine derivative BDF 9148 (10(-7) M), or of veratridine (10(-6) M), the threshold ouabain concentration to induce toxicity was lowered by a factor of 2. This effect can be explained by the observation that specific equilibrium [3H]ouabain binding in intact atria was elevated by these compounds in the appropriate concentrations. The binding results were analyzed by means of a previously established model of "positive cooperative ouabain binding to intact myocardium," which describes the relationship between cellular sodium homeostasis and ouabain binding. The extent to which the compounds increased ouabain binding was in good quantitative agreement with the observed shift in the threshold concentration of ouabain toxicity. The increase of specific [3H]ouabain binding is likely initiated by a gain in cytosolic sodium. It takes place at the cellular level only, since a direct enhancement of [3H]ouabain binding to isolated cardiac membranes was not found. In conclusion, at least under some conditions, new inotropic drugs acting as sodium channel modulators can increase the risk of digitalis toxicity.
Modulation of ouabain binding in beating ventricular myocardium from guinea-pigs: effects of lidocaine and monensin.
To further elucidate the interdependence between digitalis sensitivity and the cellular Na+ load, the influence of two Na+ load modifying drugs, monensin and lidocaine, on the concentration-dependence of ouabain binding and ouabain effects was studied in beating ventricular strips from guinea-pig heart. Monensin (3 x 10(-6)M), a Na+ ionophore known to elevate Na+ influx, enhanced 3H-ouabain binding (by approximately 40%) as well as the ouabain effect at non-toxic ouabain concentrations, and it shifted the threshold for toxicity towards threefold lower ouabain concentrations. Lidocaine (2 x 10(-4)M), a Na+ channel blocker, lowered ouabain binding by about one third, and it extended the ouabain concentration range tolerated without toxicity by a factor of three. In the concentrations used, neither compound exerted any direct effect on ouabain binding studied in isolated cardiac membranes. The binding data obtained in the muscle strips were well fitted by a mathematical model which quantifies the dependence of ouabain binding on the underlying (Na+ +K+)-ATPase activity. These findings provide evidence for an indirect drug-induced modulation of ouabain binding via the interference with the cellular Na+ load.
Different mechanisms of protection by monoclonal and polyclonal antibodies during the course of herpes simplex virus infection.
Young adult C57BL mice intravaginally inoculated with herpes simplex virus type 1 and passively immunized with a monoclonal antibody directed against herpes simplex virus type 1 glycoprotein gB were shown to be more effectively protected against infection as compared with mice treated with polyclonal immune serum. In contrast to polyclonal antiserum, the monoclonal antibody markedly restricted viral multiplication in the infected mucous membranes. Consequently, skin lesions were completely prevented, and the extent of ganglionic infection was significantly reduced. The mechanism by which a monoclonal antibody, specific to glycoprotein gC, effected protection also differed from that of the hyperimmune serum, since premature latency was not induced. The data provide strong evidence that the mechanisms of protection mediated by antibodies depend on their epitope specificity. The inhibition of active antibody response after passive immunization was inducible by polyclonal antibody only, not by monoclonal antibodies.
A related epitope is consistently present on glycoprotein C of herpes simplex virus type 1 and 2.
A monoclonal antibody (VE8) directed to glycoprotein C of herpes simplex virus type 1 (HSV-1) cross-reacted with all HSV type 2 (HSV-2) strains tested. Positive reaction was also observed with all investigated HSV-1 strains, indicating that the related epitope is consistently present in HSV-1 and HSV-2.
Inducible expression of herpes simplex virus type 1 glycoprotein C in NIH 3T3 cells.
Antibodies directed against the glycoprotein C (gC) of herpes simplex virus type 1 (HSV-1) are known to be mainly HSV-1-specific, whereas antibodies against other major HSV-1 glycoproteins cross-react with HSV-2 antigens. To investigate the immunological features of gC-1, the gene encoding gC-1 was isolated and cloned from DNA of cells infected with HSV-1. The 3.6 kbp SalI fragment R of HSV-1 DNA was modified in order to place the gene under transcriptional control of the glucocorticoid dependent promoter of the MMTV-LTR. NIH 3T3 cells were transfected with the resulting plasmid. Cell lines established by selection for the vector-encoded marker gene were tested for the ability to synthesize gC-1 after addition of dexamethasone to the growth medium. Glycoprotein-enriched cell extracts of several clones were shown to contain gC-1 by immunoblotting using a gC-1-specific monoclonal antibody. One cell line was used to show the presence of gC-1 also in the culture supernatant. gC-1 synthesis decreased after several passages of the cells but could be restimulated by the addition of 5-azacytidine to the cultures.
Interaction of the hexamethonium derivative W84, an allosteric effector at muscarinic cholinoreceptors, with rat brain nicotinic binding sites.
The hexamethonium derivative W84 (hexamethylene-bis-[dimethyl-(3-phthalimidopropyl)-ammonium bromide]) combined with atropine has an overadditive protective action against organophosphorus intoxications. It affects allosterically the binding of (-) [3H]N-methylscopolamine [(3H]NMS) to muscarinic cholinoceptors. Because nicotinic receptors are involved in organophosphorus intoxications, the interaction of W84 with nicotinic cholinoceptors was investigated. (-) [3H]nicotine (2.5 nM) was used to label nicotinic binding sites in rat brain membranes in 50 nM Tris, pH 7.3 at 23 degrees. Under control conditions, (-) [3H]nicotine-binding revealed a KD of 4 X 10(-9) M and a Bmax of 53 fmol/mg membrane protein. W84 inhibited (- ) [3H]nicotine-binding with an IC50 of 3 X 10(-5) M by reducing the binding affinity. The IC50 of hexamethonium was 20 X 10(-5) M. At 10(-4) M, W84 did not affect the dissociation rate of (-)[3H]nicotine, suggesting a lack of allosteric activity. For sake of comparison, the action of W84 was checked on [3H]NMS-binding (control: KD approximately 1 X 10(-9) M, Bmax approximately 500 fmol/mg prot). W84 inhibited the binding of [3H]NMS (0.5 nM) with an IC50 of 1.5 X 10(-9) M. At 10(-4) M, W84 prevented [3H]NMS-dissociation almost completely, thus displaying the allosteric action at muscarinic cholinoceptors. In conclusion, the results of the (-)[3H]nicotine-binding experiments point to a pure competitive action of W84 at nicotine cholinoceptors, lacking any allosteric effect. This competitive action may contribute to the protective effect of W84 in organophosphorus poisoning.
Human accumulation potential of xenobiotics: potential of catamphiphilic drugs to promote their accumulation via inducing lipidosis or mucopolysaccharidosis.
1. Drug accumulation without a concomitant elevation of blood level may occur if the capacity of the tissue to bind drug increases during chronic treatment. 2. This special type of accumulation is found with cationic-amphiphilic drugs, which induce the formation of lysosomal inclusion bodies containing undergraded lipids or mucopolysaccharides (drug-induced lipidosis or mucopolysaccharidosis, respectively); the stored material provides the additional binding sites for the drug. 3. Factors determining the potential for inducing lipidosis or mucopolysaccharidosis are: (a) affinity of the drugs to phospholipid layers (governed by hydrophobicity) or mucopolysaccharides (drug-induced lipidosis or mucopolysaccharidosis, respectively); the free intra-lysosomal concentration, which is elevated compared with the blood level due to lysosomal trapping (especially with dicationic drugs); (c) the therapeutically required drug concentration in the blood: the therapeutic concentrations are high with drugs that do not act via binding to specific high-affinity receptors.
Comparison between the activities of cationic amphiphilic drugs to affect phospholipid-membranes and to depress cardiac function.
The activity of cationic amphiphilic compounds to affect artificial phospholipid-membranes was compared with the membrane-stabilizing cardiodepressant potency of the drugs. The twenty-one investigated catamphiphilic compounds belonged to various pharmacological groups including antiarrhythmic, local anaesthetic, beta-blocking, antimalarial, and psychoactive drugs. The perturbing action of the drugs on phospholipid-membranes was evaluated by determining the drug-effect on the temperature of the phase-transition from the gel to the liquid crystalline state in liposomes of dipalmitoylphosphatidic acid by means of differential scanning calorimetry. The ability to interact with the polar headgroups of phospholipid-membranes was measured by recording the effects of the cationic compounds on the binding of 45Ca2+ to monomolecular layers of phosphatidylserine. The cardiodepressant action was observed in Langendorff-preparations of guinea-pig hearts. The drug-effect on excitability was indicated by the elevation of the threshold-intensity of 50 Hz alternating current to induce ventricular arrhythmia. For the sake of comparison, the negative chronotropic and inotropic effects were evaluated. There was only a moderate correlation found between the activities of the drugs to reduce the transition temperature and to inhibit 45Ca2+ -binding (r = 0.69). This result probably reflects that both methods look upon different consequences of the drug-phospholipid interaction. The membrane-stabilizing, anti-excitatory potency corresponded favourably with the ability of the drugs to affect the phospholipids. Almost 80% of the variance between the anti-excitatory potencies could be accounted for by the drug-phospholipid interactions. The negative chronotropic and inotropic effects accompanying the anti-excitatory actions were similar for most of the drugs. The results of the study are compatible with the hypothesis that the interaction with phospholipid-membranes is a major determinant of the membrane-stabilizing cardiodepressant potency of cationic amphiphilic drugs.
Allosteric stabilization of 3H-N-methylscopolamine binding in guinea-pig myocardium by an antidote against organophosphate intoxication.
W84 (hexamethylene-bis-[dimethyl-(3-phthalimidopropyl)-ammonium bromide]) protects overadditively against an organophosphate-intoxication when applied in combination with atropine. Further experimental evidence led to the hypothesis that W84 exerted an allosteric effect on muscarinic acetylcholine receptors. In order to investigate the action of W84 on the receptor level, binding studies with 3H-N-methylscopolamine were performed in homogenized and intact guinea-pig myocardium. For sake of comparison three bispyridinium oximes were included, i.e. Uno3 (trimethylene-bis-[4-hydroxyiminomethyl-pyridinium] dibromide mono-2,6-dichlorobenzylether), obidoxime, and TMB4. In cardiac membrane suspensions, all compounds inhibited 3H-NMS-binding after 2 hrs of incubation concentration-dependently by reducing its affinity, whereas leaving the number of binding sites unaltered. However, with increasing concentrations W84 suppressed 3H-NMS-binding less than expected for a competitive antagonist. Kinetic studies revealed that W84 did not only slow the association of 3H-NMS, but additionally retarded its dissociation over the entire range of concentrations that inhibited 3H-NMS-binding. At lmM, W84 augmented the half life time of the 3H-NMS-receptor complexes from a control value of 4 min to more than 120 min. The stabilization of the radioligand-receptor complexes is indicative of an allosteric effect of W84. Obidoxime, TMB4 and Uno3 at low concentrations acted like competitive inhibitors of 3H-NMS-binding. From 10(-5)M onwards, Uno3 retarded 3H-NMS-dissociation concentration-dependently. It is concluded that the effect of bisquaternary compounds on 3H-NMS-association and -dissociation is mediated via binding to two separate sites, i.e. the muscarinic receptor site and an allosteric effector site, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)