Sarcomeric oscillations in frog skeletal muscle fibers

Brief asynchronous, small-amplitude, cyclic, longitudinal displacements of the striations of frog skeletal muscle fibers were observed with ordinary light microscopy after application of caffeine and certain quaternary ammonium compounds. With time these oscillations became synchronized and evolved into peristaltic-like movements. The oscillations were influenced by sarcomere length, temperature, external concentration of calcium ions, membrane potential, and disruption of the transverse tubules.

Subcellular sites for synthesis of chondromucoprotein of cartilage

Microsomes from embryonic cartilage have been subfractionated to yield smooth microsomes and rough microsomes. The in vitro enzymic activities involved in chondroitin sulfate biosynthesis have been assayed in these subfractions. The results demonstrate that all of the activities necessary for linkage to protein as well as for completion of the polysaccharide chain are present in both the rough and smooth fractions. Only in the case of the polymerization of N-acetylgalactosamine and glucuronic acid could enzyme assays be done independent of endogenous acceptor. This enzyme(s) was equally distributed between the rough and smooth fractions. The activities for the addition of xylose and galactose to protein were highest in the rough fraction while that for sulfation was highest in the smooth fraction. These findings suggest that polysaccharide chain-initiation occurs in the rough endoplasmic reticulum and that chain completion occurs in the smooth reticulum. This pattern is consistent with modern theories of synthesis, transfer, and export of extracellular macromolecules.

Cytochemical studies of lysosomes, golgi apparatus and endoplasmic reticulum in secretion and protein uptake by adrenal medulla cells of the rat

The adrenalin-producing cells of the rat adrenal medulla have been studied by light and electron microscopy. Frozen sections of glutaraldehyde-perfused material were incubated for demonstration of "marker" enzymes for lysosomes (acid phosphatase, aryl sulfatase) and Golgi apparatus (thiamine pyrophosphatase). In addition, the uptake and fate of intravenously administered horseradish peroxidase was followed. Acid phosphatase activity is demonstrable in secretory granules, Golgi saccules, vesicles in the Golgi area and in the agranular tubules and cisternae (GERL) from which secretory granules appear to form at the inner surface of the Golgi apparatus. Endoplasmic reticulum with ribosomes on only one surface is closely apposed to both inner and outer aspects of the Golgi apparatus. Peroxidase is taken up in vesicles, tubules and "cup-like" bodies. The latter apparently transform into multivesicular bodies. A possible source of the acid phosphatase found in multivesicular bodies is the small vesicles from the Golgi apparatus or GERL.

Localization of hyaluronic acid in synovial cells by radioautography

Cultured human synovial cells secrete hyaluronic acid (HA) into the culture medium. Glucosamine-6-(3)H was shown to be a direct and relatively specific precursor of HA-(3)H by the following observations: the susceptibility of nondialyzable radioactivity in the medium to hyaluronidase, its migration with hexuronic acid on zone electrophoresis in polyvinyl chloride, its exclusion from Sephadex G-200, and the localization of radioactivity to glucosamine after hydrolysis of the labeled polysaccharide. The presence of intracellular HA-(3)H was established by sequential extraction of labeled cells and by radioautography of synovial cell cultures digested with hyaluronidase in situ. When cells were exposed to medium lacking glucose, glucosamine-(3)H-uptake was enhanced; and this made possible electron microscopic radioautographic studies. These studies demonstrate the early and continued presence of HA-(3)H within the Golgi apparatus.

Ion effects on calcium accumulation by cardiac sarcoplasmic reticulum

The effects of monovalent cations on the active calcium-accumulating ability of cardiac sarcoplasmic reticulum were assessed. Grana prepared in an ion-free system accumulated calcium when ATP and Mg(++) were present. Sodium ion and to a lesser extent lithium but not K(+) reduced the amount of calcium taken up. The reduction of calcium binding by Na(+) is not due to inhibition of uptake but to a rapid release of the radiocalcium bound. The amount of calcium released by sodium does not appear to be enough to explain contraction on the basis of sodium influx into muscle, but may be significant in the regulation of tension.

Intracellular transport of secretory proteins in the pancreatic exocrine cell. I. Role of the peripheral elements of the Golgi complex

It has been established by electron microscopic radioautography of guinea pig pancreatic exocrine cells (Caro and Palade, 1964) that secretory proteins are transported from the elements of the rough-surfaced endoplasmic reticulum (ER) to condensing vacuoles of the Golgi complex possibly via small vesicles located in the periphery of the complex. To define more clearly the role of these vesicles in the intracellular transport of secretory proteins, we have investigated the secretory cycle of the guinea pig pancreas by cell fractionation procedures applied to pancreatic slices incubated in vitro. Such slices remain viable for 3 hr and incur minimal structural damage in this time. Their secretory proteins can be labeled with radioactive amino acids in short, well defined pulses which, followed by cell fractionation, makes possible a kinetic analysis of transport. To determine the kinetics of transport, we pulse-labeled sets of slices for 3 min with leucine-(14)C and incubated them for further +7, +17, and +57 min in chase medium. At each time, smooth microsomes ( = peripheral elements of the Golgi complex) and rough microsomes ( = elements of the rough ER) were isolated from the slices by density gradient centrifugation of the total microsomal fraction. Labeled proteins appeared initially (end of pulse) in the rough microsomes and were subsequently transferred during incubation in chase medium to the smooth microsomes, reaching a maximal concentration in this fraction after +7 min chase incubation. Later, labeled proteins left the smooth microsomes to appear in the zymogen granule fraction. These data provide direct evidence that secretory proteins are transported from the cisternae of the rough ER to condensing vacuoles via the small vesicles of the Golgi complex.