ISOLATION AND CHARACTERIZATION OF THE SARCOPLASMIC RETICULUM OF SKELETAL MUSCLE

The sarcoplasmic reticulum (SR) of rabbit skeletal muscle was studied after isolation of a vesicle fraction and of vesicular subfractions by means of differential and density gradient centrifugations. The different fractions were examined electron microscopically by negative and positive staining; their content in protein and phospholipid and their ability to bind Ca++ were determined. After homogenization, differential centrifugation yielded a "sarcovesicular fraction" (SVF) which was mainly composed of numerous vesicles of different types mixed with fibrous proteins and mitochondrial fragments. This SVF contained 2% of the protein and 25% of the phospholipid of the initial tissue extract. It had a high Ca++ binding activity that was preserved for several days by storage in the presence of oxalate. After centrifugations of the SVF on sucrose density gradients, two vesicular subfractions were obtained which were characterized by different sedimentation rates, isopycnic banding, morphology, and composition in protein and phospholipid. (a) The low-density subfraction (ρ 1.10–1.12) contained a heterogeneous population of membranous structures: thick- and thin-walled vesicles, tubular formations, triads, and plasma membranes. Its content in protein and phospholipid was very low. (b) The high-density subfraction (ρ 1.13–1.17) was a very pure subfraction composed only of thin-walled vesicles. Its content in phospholipid was high and the ratio of phospholipid-phosphorus to protein was about 20. The calcium-binding activity found in the total SVF was recovered only in this latter homogeneous subfraction. The origin of these two subfractions from the SR is discussed

Ultrastructure de la glande mammaire du rat sous l'action d'un carcinogène chimique

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Effects of insulin, prolactin, progesterone, and estradiol on DNA synthesis in organ culture of 7,12 dimethylbenz(a)anthracene induced rat mammary tumors

The effect of various hormones or hormone combinations on DNA synthesis was investigated in organ cultures of 20 dimethylbenz(a)anthracene-induced rat mammary tumors. Three tumors were insulin independent and were totally insensitive to all other hormones tested. Seventeen tumors were insulin dependent for DNA synthesis and, in the presence of insulin, displayed variable responses to the other hormones. Nine of 12 such tumors were significantly stimulated by the combination of prolactin and progesterone. Given alone, these hormones were effective in only 25% of the tumors tested. Estradiol used at 2 dose levels, 0.001 or 1.0 μg/ml, acted in a reverse manner to progesterone and proved inhibitory in combination with prolactin in 40% of cases. It was ineffective alone except in 1 of 10 cases in which a stimulatory effect was recorded. A comparison in 4 tumors between estimation of DNA synthesis ([3H]thymidine incorporation into DNA) and colchicine-blocked mitoses demonstrated a good concordance. These results are discussed in terms of variations in the degree of hormone responsiveness of individual tumors and of the known hormone-dependent properties of the 7,12-dimethylbenz(a)-anthracene tumors in vivo. © 1976, American Association for Cancer Research. All rights reserved.SCOPUS: ar.jSCOPUS: ar.jinfo:eu-repo/semantics/publishe

Morphological changes of the anterior pituitary, adrenals and mammary glands in rats after DMBA administration

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Redistribution of epidermal growth factor immunoreactivity in renal tissue after nephrotoxin-induced tubular injury

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