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Biomedical subjects

G Stark

Publications and source records attributed to G Stark.

At least 163 records · Page 9Linked to original sources
PubMed1980

Fall in the incidence of Crohn's disease.

Chronic transmural inflammatory bowel disease was first described in Scotland by Dalziel in 1913. A study has been made of new cases arising in the Aberdeen area during the 21 years, 1955--75, and is continuing. The number of new cases developing each year rose from 1.2 per 100 000 population at the beginning of the study to a peak of 4.5 in 1969. Thereafter it gradually declined, the mean incidence during the three year period 1973--75 being only 2.6 per 100 000. The decline has affected both males and females. It has been more marked in city dwellers than in the rural population. The former preponderance of city cases has almost disappeared. Disease apparently confined to the small intestine is less common than in 1955, when it constituted 77% of the cases recorded. Today the large intestine or combined forms make up 75% of the new cases which are seen. There is no obvious explanation for the fall in incidence or change in site.

Crohn Disease↗
PubMed1980

Effects of lipid structure on the kinetics of carrier-mediated ion transport.

The mechanism of alkali-ion transport mediated by valinomycin (or similar macrocyclic carriers) may be studied using artificial planar bilayer membranes. The rate constants of the single transport steps (association and dissociation of the ion-carrier complex, translocation of free and complexed carrier) can be determined from electrical relaxation experiments. The turnover number of valinomycin which may be calculated from the rate constants is found to be 10(4)-10(5) s-1. Carriers of the valnomycin-type offer the possibility of studying the relationship between membrane structure and transport kinetics. Increasing the chain-length of the lipid strongly reduces the translocation rate constants of the free and the loaded carrier, and also (in the case of lecithin membranes) the association rate constant. Increasing the number of double bonds in the fatty-acid residue of the lipid leads to an inrease of the translocation rate constants. These effects are discussed in terms of microviscosity of the membrane. Addition of cholesterol to monoglyceride membranes seems to affect both the microviscosity and the dipolar potential at the membrane-solution interface.

Carrier Proteins↗
PubMed1979

[Ten years experience with laparoscopy in the state women's clinic of Nurenberg].

During the period from 1968--1977 2400 laparoscopies were performed. Of these 10.7% were for diagnostic purposes only, in 3.6% of the cases laparoscopy was combined with biopsie and in 85.7% with tubal sterilization. Deaths or serious bleedings did not occur, laparotomies were not necessary. Total insignificant complications amounted to 1.6% (1.3% small bleedings which did not necessitate an operation and in 0.3% clinical signs of peritonitis, these disappeared after 3 to 15 days). In 0.7% laparoscopy was interrupted because of poor vision. Nine of 2055 women became pregnant after sterilization (4.5 pregnancies/1000 sterilizations). In 2 cases the ligamentum rotundum was coagulated, in 7 cases recanalization was histologically confirmed. Until Oct. 1975 coagulation was unipolar, afterwords bipolar. In 45.3% the patients had undergone an operation before, like Ceasarian section, gallbladder operation, appendectomy or umbilical hernia operation. Patients with longitudinal incision, with preceding peritonitis or ileus were excluded from laparoscopy. Laparoscopy was performed by all assistents during their last year of clinical instruction. Their first 30 laparoscopies were done under control, every assistent performed about 100 laparoscopies.

Female↗
PubMed1979

Kinetics of ion transport in lipid membranes induced by lysine-valinomycin and derivatives.

Lysine-valinomycine and two N epsilon-acyl derivatives are compared with respect to their potency to transport Rb+ ions across thin lipid membranes. Lysine-valinomycin acts as a neutral ion carrier only above a pH of about 7 of the aqueous solutions, while at lower pH the molecules seem to be positively charged due to a protonation of the epsilon-NH2 group of the lysine residue. A kinetic analysis based on voltage jump relaxation experiments and on the nonlinearity of the current-voltage characteristics showed that the conductance increment delta per carrier molecule for uncharged lysine-valinomycin is similar to that of natural valinomycin. The attachment of a rather bulky side group such as the dansyl or para-nitrobenzyloxycarbonyl group reduced delta by approximately one order of magnitude. Some of the relaxation data of the valinomycin analogues were influenced by an unspecific relaxation of the pure lipid membrane. This structural relaxation represents a limitation to the possibility of analyzing specific transport systems in thin lipid membranes by the voltage jump or charge pulse techniques. It is shown that the time dependence of this structural relaxation--which was first published by Sargent (1975)--is at variance with a three capacitor equivalent circuit of the membrane, which was suggested by Coster and Smith (1974) on the basis of a.c. measurements. A modified equivalent circuit has been found to represent a satisfactory analogue for the current relaxation in the presence of valinomycin. It turned out, however, that such an equivalent circuit provides little insight into the molecular mechanism of transport.

Biological Transport↗
PubMed1979

Kinetics of transport of hydrophobic ions through lipid membranes including diffusion polarization in the aqueous phase.

Previous interpretations of the kinetics of transport of hydrophobic ions through membranes have been based on one of three limiting assumptions. Either diffusion in the aqueous phase was taken to be rapid, or ionic motion was constrained to the membrane or a steady state was presumed to be established within the membrane. We present a general treatment of the coupled diffusion process through both the aqueous phase and the membrane; our theory contains the previous results as limiting cases. It is applied to voltage jump-current relaxation experiments on black lipid membranes in the presence of dipicrylamine or sodium tetraphenylborate. We have attempted to establish the rate of desorption from the membrane. For the system phosphatidylserine/tetraphenylborate, the rate of desorption and the rate of translocation were found to be comparable.

Journal Article↗
PubMed1977

Temperature-jump experiments on thin lipid membranes in the presence of valinomycin.

Temperature jump relaxation experiments on planar lipid membranes in the presence of valinomycin were performed using the absorption of a strong light flash as an energy source for the generation of the T-jump. The relaxation of the current carried by valinomycin/Rb+ complexes was measured. The results were interpreted on the basis of a transport model which was also analyzed by voltage jump relaxation experiments. The study shows that the application of the T-jump technique provides valuable information about transport kinetics as well as the dynamics of the membrane structure. At the given experimental conditions the relaxation of the current is believed to reflect a temperature-dependent transition of the membrane to a new conformational state of low order. The relaxation could be resolved with the present technique only at low temperatures and for membranes of high microviscosity.

Biological Transport↗
PubMed1977

[Follow-up of 2300 vaginal and abdominal hysterectomies].

The report deals with the 2330 hysterectomies, performed in the "Women's Hospital of the City of Nuernberg", in 1968 through 1973. One thousand extirpations were done the abdominal way, whereas 1330 were done using the vaginal method. The average age of the patients was 50 years. The distribution of the parity of the abdominal hysterectomies was about equal, whereas the parity of the vaginal operations was 11 times higher, mainly because of technical reasons. The main indications of the vaginal extirpations were: descensus, uterus myomatosus and non invasive cancer; the one of the abdominal extirpations was uterus myomatosus, benign and malign ovarial tumors and cancer of corpus uteri. The total ratio of complications (including abscess of the abdominal wall, seromes etc.) amounts ot 19,1% of the abdominal operations, 9,6% of the vaginal operations. The total mortality of the abdominal operations was nearly 1,7% the one of the vaginal operations approached 0,37%. In 50% respectively 80% the cause of death was an acute emboly of the lungs.

Adult↗
PubMed1976

Facilitated transport of di- and trinitrophenolate ions across lipid membranes by valinomycin and nonactin.

The conductance of black lipid membranes in the presence of 2,4,6-trinitrophenol (or 2,4-dinitrophenol) is considerably enhanced, if the cation carriers valinomycin, enniatin B or nonactin are added. The effect is, however, largely independent of the cation concentration and is identical for the cations Li+, Na+ and Ba2+. This finding, as well as the sign and magnitude of the diffusion potential in the presence of a gradient of picrate are consistent with the assumption that the transport of picrate anions is facilitated by the above-mentioned macrocyclic compounds, but that cations are not directly involved. A model is suggested which, based on the generation of mobile defect structures by the incorporation of large molecules, allows one to explain facilitated transport without the assumption of stable chemical bonds between a carrier and its transported substrate. If K+ is present in the aqueous phase, the conductance is largely determined by the permeation of the cation complexes of valinomycin and nonactin. The conductance is, however, increases by adsorption of picrate anions to the membrane surface. The negative surface potential generated by the adsorption layer seems to be responsible for the saturation of the conductance at high picrate concentrations in the absence of valinomycin and nonactin.

Anti-Bacterial Agents↗
PubMed1976

Optical and electrical studies on dansyllysine-valinomycin in thin lipid membranes.

Dansyllysine-valinomycin, a fluorescent analogue of the ionophore valinomycin was synthesized and incorporated into black lipid membranes. Its concentration inside the membrane was measured fluorometrically and was also determined from electrical relaxation experiments, which were analyzed on the basis of a previously proposed carrier model. The results of both methods agreed within less than one order of magnitude. This appears satisfactory in view of the sources of error inherent in both procedures. A conductance increment per carrier molecule of about 3 - 10(-17) omega-1 was obtained for dansyllysine-valinomycin in diphytanoyllecithin membranes at 25 degrees C and 1 M RbCl in the aqueous phases. This is about 400 times smaller compared to unmodified valinomycin in monoolein membranes. The difference is mainly caused by the change in the membrane properties and to a smaller extent by the structural modification of the carrier.

Electric Conductivity↗
PubMed1975

Kinetics of macrotetrolide-induced ion transport across lipid bilayer membranes.

Ion transport across lipid bilayer membranes in the presence of macrotetrolide antibiotics has been studied by stationary conductance and nonstationary relaxation methods. The results are discussed on the basis of a carrier model which has already been successfully applied to valinomycin induced ion transport. Again a kinetic analysis has been performed from which the single rate constants of the carrier model could be derived. In addition the equilibrium constant of complex formation in the aqueous phase could be determined. Measurements have been made for 4 macrotetrolides, for several ions and for various chain lengths of the lipid molecules composing the membrane.

Anti-Bacterial Agents↗
PubMed1975

Haemangioma with coagulopathy: sustained response to prednisone.

Two cases of giant haemangioma with thrombocytopenia are described. A satisfactory and sustained response to prednisone was achieved in respect of both coagulation abnormalities and tumour size. It is proposed that prednisone is effective by enhancement of thrombosis and reduction of fibrinolysis within the tumour, thus promoting a natural form of resolution. It is suggested that prednisone therapy should be first-choice treatment of complicated haemangiomas.

Abdominal Muscles↗