[In vitro corrosion tests of different alloy crowns over amalgam cores].
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Chromium↗
Biomedical subjects
T Beyer
Publications and source records attributed to T Beyer.
Effects of bivalent cations on post-rest adaptation in guinea-pig heart muscle.
In isolated papillary muscles of guinea-pig hearts, the inotropic effects of bivalent cations, Ca2+, Ba2+, Sr2+, and Ni2+, were investigated during post-rest adaptation in order to study their individual action on excitation-contraction coupling. Upon exposure to each cation studied, the force of contraction was transiently enhanced, whereas the steady state force was influenced differently: it increased with Ca2+, Ba2+ and Sr2+ and was depressed by Ni2+. The transmembrane action potentials (measured at 90% repolarization) were slightly prolonged by Sr2+ and even more by Ba2+, and were shortened by Ca2+ and Ni2+. After 10 min rest, the post-rest contractions consisted of a late peak (PII) that was enhanced in high Ca2+-solution an by Sr2+. Ni2+ and Ba2+ depressed PII and during adaptation to pre-rest controls an early peak of contraction (PI) prevailed. There was no simple relation between post-rest adaptation of force and the duration of action potential in the presence of the bivalent cations tested. During post-rest adaptation the two components of contraction can be separated. The results are interpreted in terms of a model of excitation-contraction coupling which derives Ca ions for contractile activation from two sources: transmembrane calcium influx and calcium release from cellular stores. From the different effects on post-rest adaptation it is concluded that the individual cations influence excitation-contraction coupling more specifically and not merely by "screening-off" the negative surface charges.
Action Potentials↗
The effects of the cardiotonic dihydropyridine derivatives Bay k 8644 and H160/51 on post-rest adaptation of guinea-pig papillary muscles.
In isolated guinea-pig papillary muscle, the effect of the two dihydropyridine derivatives Bay k 8644 (0.03-10 mumol/l) and H160/51 (0.1-3 mumol/l) on transmembrane action potentials and force of contraction were investigated at regular stimulation (1 Hz) and after a period of rest (10 min). The following results were obtained: At regular stimulation of the preparations, Bay k 8644 and H160/51 enhanced force of contraction without affecting time-to-peak tension. The time required for relaxation and the action potential duration were prolonged. These effects were transient with exposure to high concentrations of Bay k 8644 (greater than 3 mumol/l). The amplitude of the post-rest contraction thought to depend entirely on transmembrane calcium influx was small under control conditions and increased because of prolongation in time-to-peak tension in the presence of either dihydropyridine derivative. Isoprenaline (30 nmol/l) - as opposed to Bay k 8644 and H160/51 - increased the rate of force development of post-rest contractions. Bay k 8644 and H160/51 prolonged the duration of the first action potential after 10 min of rest. In the course of adaptation to steady state stimulation this prolongation transiently increased further resulting in a biphasic pattern which was attenuated by addition of nifedipine. With isoprenaline the biphasic pattern changed into a monotonous adaptation to pre-rest control. Our results show that the small enhancement of the post-rest contraction in the presence of Bay k 8644 or H160/51 is due to prolonged action potential duration after rest, whereas isoprenaline enhances the intensity of post-rest activation.(ABSTRACT TRUNCATED AT 250 WORDS)
3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
Responses to hypertonic solutions in guinea-pig atria: changes in action potentials, force of contraction and calcium content.
In left atria of guinea-pig hearts we studied the effects of Tyrode solution made hypertonic by the addition of mannitol (50 to 300 mosm/l). Electrical and mechanical performance were investigated at 0.1, 1 and 3 Hz. Up to 150 mosm/l a positive inotropic effect was observed, addition of 300 mosm/l caused a positive inotropic response followed by a long lasting negative inotropic effect. The positive inotropic effect depended on the frequency of stimulation: at the low frequency of 0.1 Hz the increase in force of contraction was so large, that in hypertonic solution the absolute value of developed tension at 0.1 Hz was actually larger than at 3 Hz. With 150 mosm/l mannitol the time to peak tension and the twitch duration were prolonged. These effects were also most prominent at 0.1 Hz. The action potential duration was shortened; the membrane hyperpolarized. The observed changes in action potential duration and the membrane hyperpolarization may reflect changes in cation concentration due to cellular dehydration. The propagation velocity of excitation was reduced in the absence of a detectable decrease in maximum rate of depolarization during the upstroke of the action potential. The cells did not behave as perfect osmometers because loss of tissue water as estimated from wet weight and dry weight measurements was smaller than expected for a 1.5-fold increase in tonicity. After having established complete exchange of tissue calcium with 45Ca, hypertonicity-induced changes in the cellular calcium content could be determined by changes in 45Ca content. At both frequencies of stimulation, the cellular calcium content increased to the same extent.(ABSTRACT TRUNCATED AT 250 WORDS)
Action Potentials↗
[Cytochemical study of various stages of the life cycle of Toxoplasma gondii. 3. Phosphatases in the entozoa].
Three methods were used to detect acid phosphatase in toxoplasma endodozoites of strain SS-119 harvested on day 4 after mouse inoculation. The modified lead nitrate method detected the enzymatic activity in host cells only; Gomori metal salt technique revealed the enzyme almost exclusively in the parasite, whereas the Standard Naphthol AS-BI phosphate method suggested the presence of the enzyme simultaneously in the two, though not regularly in the parasites. The enzymatic activity when present was visualized as few coloured granules mainly in the anterior cytoplasmic area on the body and at the periphery, leaving the nuclear zone unstained. Alkaline phosphatase distribution, detected with one method only (Standard Naphtol AS-BI phosphate), appeared less convincing in the parasite than in the host cell. In host cells harbouring endozoites, no increased activity was observed in the immediate closeness of the intracellular parasites.
Acid Phosphatase↗
Whole-body fluorine-18 fluordeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) in staging of advanced uveal melanoma.
Fluorine-18 fluordeoxyglucose positron emission tomography (FDG-PET) is an useful tool in diagnosing and monitoring of malignant cutaneous melanoma. However, the feasibility and usefulness of FDG-PET in uveal melanoma is not yet established. We present a patient with suspected advanced uveal melanoma who underwent combined FDG-PET/computed tomography (CT) for staging. FDG-PET/CT images demonstrated vital intraocular tumor. Anatomical assignment of the malignancy to the choroid was possible by means of the coregistered computed tomography. Furthermore, PET revealed an unknown otherwise undetected vital liver metastasis. We conclude that combined FDG-PET/CT has potential to further improve staging and therapy planning in patients with advanced uveal melanoma.
Aged↗