Three different types of single living muscle fibre were dissected from the iliofibularis muscle of Xenopus laevis. The fibres were mounted in a glass chamber and their rate of oxygen consumption was determined as a function of twitch frequency at 20 degrees C. The rate of oxygen consumption increased with twitch frequency until it levelled off and reached a maximum. The maximum rate of oxygen consumption varied between fibres (0.019 to 0.161 nmol O2 s-1 mm-3) and was reached at different twitch frequencies (less than 0.2 to 5.7 stimuli s-1). After the determination of the maximum rate of oxygen consumption, the succinate dehydrogenase activity in cross sections of the fibre was determined by means of a quantitative histochemical method. A proportional relationship between the maximum rate of oxygen consumption and the succinate dehydrogenase activity was found. The maximum rate of oxygen consumption and the succinate dehydrogenase activity are also proportional to the volume density of mitochondria in the three fibre types reported by Smith and Ovalle (1973; J. Anat., Lond. 116, 1-24). It is concluded that quantitative histochemistry of succinate dehydrogenase reliably predicts the maximum rate of oxygen consumption of muscle fibres in Xenopus laevis and that the maximum rate of oxygen consumption of single muscle fibres is determined by the volume density of mitochondria.
Endometrial hyperplasias and carcinomas have been investigated by quantitative microscopical methods. The aim of this study was to develop an objective method of histopathological diagnosis because of the great subjective variability of these endometrial conditions. A total of 79 cases were studied. Only those were included, which, after re-examination of the material by different pathologists, were regarded as mild atypical hyperplasia (38 cases), marked atypical (adenomatous) hyperplasia (11 cases), well and moderately differentiated adenocarcinoma (19 and 11 cases, respectively). There are many significant differences between these four groups. Stereological features contained the most important information, whilst nuclear features were less successful discriminators. The volume percentage of the epithelium and of the glands and the inner surface density of the glands showed the most significant differences between adenomatous hyperplasia and well differentiated carcinoma. On the basis of these findings, a quantitative model is suggested which might give more insight into the development of these abnormalities, assuming a gradual transition from one to another. The great advantage of the quantitative analysis of data over subjective impressions, it that is is objective, and provides consistently reproducible results. The present results may be especially useful when histopathological diagnosis is in doubt. It is concluded that application of quantitative microscopy in the discrimination of endometrial hyperplasia and carcinoma in histopathology is feasible.
The iliofibularis muscle of Xenopus laevis is reported to contain five types of fibres which have different force-velocity relationships. Ten fibres of each type were selected on the basis of succinate dehydrogenase activity, cross-sectional area and location in the muscle, in order to assess the validity of the fibre type classification. Maximum calcium-stimulated myofibrillar ATPase activity (Vmax) and apparent Michaelis constant (Km) for ATP were determined for these 50 fibres from serial sections. The values obtained varied according to the type of fibre. Type 1 had the highest and type 5 the lowest values for Km and Vmax. In a separate experiment, single freeze-dried fibres were used to determine the relationship between their ATP content and apparent Km for ATP. There was a tendency for high ATP concentrations in fibres with high Km values. When myofibrillar ATPase activity was related to the maximum velocity of shortening of the five fibre types, a significant correlation was found. It is concluded that calcium-stimulated myofibrillar ATPase histochemistry allows an estimate of the maximum shortening velocity of muscle fibres from Xenopus laevis.
A quantitative modification of Meijer 's calcium-lead capture method, for the demonstration of calcium-stimulated myofibrillar ATPase activity at physiological pH, is described. A range of myofibrillar ATPase activities has been found among fast muscle fibres in two mouse hind-limb muscles. The myofibrillar ATPase activity of fast muscle fibres is 1.5-3 times higher than the myofibrillar ATPase activity of slow muscle fibres. Myofibrillar ATPase activities and succinate dehydrogenase activities of individual muscle fibres have been determined in serial sections. Activities of the two enzymes are correlated positively in soleus (fast and slow fibres), and negatively in plantaris (almost all fast) and extensor digitorum longus muscle (all fast). However, this correlation is not significant among the oxidative fibres in the extensor digitorum longus. The fibres of the latter muscle cannot be classified satisfactorily into two sub-types.
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