NUCLEOSIDE PHOSPHATASE ACTIVITIES IN RAT CARDIAC MUSCLE

Electron microscopic localization of 5'-nucleotidase in the stratum intermedium and ameloblasts

5'-nucleotidase was demonstrated at the fine structural level in the stratum intermedium and ameloblasts of the first mandibular molars of CD-1 mice. The enzyme was localized with the Wachstein & Meisel (1957) method along the plasma membranes of the cells of the stratum intermedium and ameloblasts. While 5'- nucleotidase was present throughout the stratum intermedium, only the proximal region of the plasma membranes of ameloblasts was demonstrably active for this enzyme. 5'-Nucleotidase has been implicated in transport of metabolites across cell membranes, and its localization in the present study supports this implication as well as the transport functions of the stratum intermedium and the stratum intermedium--ameloblastic interface.

On the specificity of the histochemical technique for sarcoplasmic reticular adenosine triphosphatase: a light and electron microscopic study

The specificity of the histochemical localization of the calcium activated adenosine triphosphatase (ATPase) activity of the sarcoplasmic reticulum (SR) at pH 7.4 was studied using a calcium-citro-phosphate technique. The latter involves the splitting of ATP by ATPase producing phosphate ions which then react with calcium and citrate to form an insoluble reaction product. This reaction product was detected by both light and electron microscopy. Light microscopic examination showed a darkly stained continuous reticular pattern of reaction product which surrounded individual myofibrils. This reticular pattern of reaction product was distinctly dissimilar to that found when the histochemical reactions for mitochondrial or myofibrillar ATPase were performed. Ultrastructural investigations demonstrated the presence of discrete foci of electron dense reaction product in close association with the membranes of the SR in striated muscle fibres. Only occasional flecks were seen in the vicinity of mitochondria or myofilaments. The possibility is considered that the reticular pattern of staining achieved by the calcium-citro-phosphate technique may reflect the distribution of the "extra ATPase" of the SR, an enzyme implicated in the process of calcium uptake and muscle relaxation.

Ultrastructure of the atrial, ventricular, and Purkinje cell, with special reference to the genesis of arrhythmias

An examination of the anatomy of the atrial, ventricular, and Purkinje cells reveals that the internal composition of all cardiac myofibers is qualitatively the same: all have a single nucleus, sarcomeric and mitochondrial units, and a well-developed sarcoplasmic reticulum. There are important differences, however, in the extent and distribution of the cell membrane and its derivatives in the myofiber. The presence or absence of a transverse tubular system and the variation in the number and type of intercellular linkages explain at least some of the characteristic electrical and functional properties of individual types of cells. The overall pattern of cellular organization in working atrial, ventricular, and conducting tissue is reviewed, and possible anatomic bases for current theories of normal and abnormal impulse generation and conduction in the heart are discussed.

Degenerative changes in the mitochondria of flight muscle from aging blowflies

Mitochondria from flight muscle of aging blowflies, Phormia regina, were examined morphologically and biochemically with the electron microscope. An age-dependent degeneration of the mitochondria that is characterized, in part, by the reorganization of the inner membrane into myelin-like whorls has been found. The concentric rings increase in size and number, eventually replacing the normal cristal conformation. Glycogen rosettes are frequently seen in the center of the whorl and may represent the intrusion into the mitochondria of the glycogen in the cytoplasmic matrix of the muscle. The degenerating mitochondria are not associated with lysosomal activity, as indicated by the absence of acid phosphatase. An intense acid phosphatase activity is noted, however, in the dyad, comprising elements of the T system and sarcoplasmic reticulurn. Cytochrome oxidase is active in the ultrastructurally intact portion of the mitochondrion but activity is not evident in that part of the mitochondrion that has undergone morphological change. Thus, the ultrastructural degradation of the mitochondria is correlated with a decrease in biochemical function. This suggests a correspondence between a decrease in the bioenergetic capacity of the flight muscle and a decline in the ability of the aged insect to fly.

Fine structure of rat intrafusal muscle fibers. The polar region

An ultrastructural comparison of the two types of intrafusal muscle fibers in muscle spindles of the rat was undertaken. Discrete myofibrils with abundant interfibrillar sarcoplasm and organelles characterize the nuclear chain muscle fiber, while a continuous myofibril-like bundle with sparse interfibrillar sarcoplasm distinguishes the nuclear bag muscle fiber. Nuclear chain fibers possess well-defined and typical M bands in the center of each sarcomere, while nuclear bag fibers contain ill-defined M bands composed of two parallel thin densities in the center of the pseudo-H zone of each sarcomere. Mitochondria of nuclear chain fibers are larger and more numerous than they are in nuclear bag fibers. Mitochondria of chain fibers, in addition, often contain conspicuous dense granules, and they are frequently intimately related to elements of the sarcoplasmic reticulum (SR). Striking differences are noted in the organization and degree of development of the sarcotubular system. Nuclear bag fibers contain a poorly developed SR and T system with only occasional junctional couplings (dyads and triads). Nuclear chain fibers, in contrast, possess an unusually well-developed SR and T system and a variety of multiple junctional couplings (dyads, triads, quatrads, pentads, septads). Greatly dilated SR cisternae are common features of nuclear chain fibers, often forming intimate associations with T tubules, mitochondria, and the sarcolemma. Such dilatations of the SR were not encountered in nuclear bag fibers. The functional significance of these structural findings is discussed.

Ultrastructure of dyads in muscle fibers of Ascaris lumbricoides

The dyads of Ascaris body muscle cells consist of flattened intracellular cisternae applied to the sarcolemma at the cell surface and along the length of T-tubules. In specimens prepared by conventional methods (glutaraldehyde fixation, osmium tetroxide postfixation, double staining of sections with uranyl acetate and lead hydroxide), both the sarcolemma and the limiting membrane of the cisterna exhibit unit membrane structure and the space between them is occupied by a layer of peg-shaped densities which is referred to as the subsarcolemmal lamina. The lumen of the cisterna contains a serrated layer of dense material referred to as the intracisternal lamina. In specimens fixed in glutaraldehyde, dehydrated, and then postfixed in phosphotungstic acid, with no exposure to osmium tetroxide or heavy metal stains, the membranous components of the dyads appear only as negative images, but the subsarcolemmal and intracisternal laminae still appear dense. Except for the lack of density in membranes and in glycogen deposits, the picture produced by the latter method is very much like that of tissue prepared by conventional methods.

Cardiac muscle. A comparative study of Purkinje fibers and ventricular fibers

With light and electron microscopy a comparison has been made of the morphology of ventricular (V) and Purkinje (P) fibers of the hearts of guinea pig, rabbit, cat, dog, goat, and sheep. The criteria, previously established for the rabbit heart, that V fibers are distinguished from P fibers by the respective presence and absence of transverse tubules is shown to be true for all animals studied. No evidence was found of a permanent connection between the sarcoplasmic reticulum and the extracellular space. The sarcoplasmic reticulum (SR) of V fibers formed couplings with the sarcolemma of a transverse tubule (interior coupling) and with the peripheral sarcolemma (peripheral coupling), whereas in P fibers the SR formed only peripheral couplings. The forms of the couplings were identical. The significance, with respect to excitation-contraction coupling, of the difference in the form of the couplings in cardiac versus skeletal muscle is discussed together with the electrophysiological implications of the differing geometries of bundles of P fibers from different animals.

III. Electron microscopic radioautographic study of the rat heart perfused with tritiated oleic acid

Rat hearts pulse-labeled by perfusion in vitro with 9,10-oleic acid-³H for 15 or 30 sec were shown to take up the fatty acid extensively. In hearts postperfused with unlabeled medium for 15 sec or more, 90% of the radioactivity was recovered in esterified lipids. The radioautographic reaction was localized initially over elements of the sarcoplasmic reticulum and mitochondria. After longer periods of postperfusion (2–20 min), there was concentration of silver grains over lipid droplets. In mitochondria and sarcoplasmic reticulum isolated from hearts postperfused for 1 min or more, most of the esterified lipid was in the form of triglyceride. The ratio of the specific activity of isolated sarcoplasmic reticulum triglyceride to mitochondrial triglyceride changed from a value of 3.2 to 1.3 during 5 min of postperfusion. Under conditions of hypothermia, considerable uptake of free fatty acid occurred. The radioactivity recovered in the heart was mostly in the form of free fatty acid, and the radioautographic reaction was seen over sarcoplasmic reticulum and mitochondria, but not over lipid droplets or myofibrils. The results are interpreted to show that intracellular transport of free fatty acid, which occurs also when esterification is repressed, proceeds through intracellular channels, i.e. the sarcoplasmic reticulum. Esterification of fatty acid into triglycerides occurs mostly in the sarcoplasmic reticulum, especially in the region of the dyad, in the vicinity of which lipid is stored in the form of droplets.

Localization of products of ATP hydrolysis in mammalian smooth muscle cells

The sites of lead phosphate precipitation in mouse bladder smooth muscle incubated with adenosine triphosphate and lead nitrate were studied by electron microscopy. The media constituents and incubating conditions were independently varied so that we could determine optimal conditions for histochemical demonstration of ATPase activity in agranular endoplasmic reticulum. Specimens of glutaraldehyde-fixed bladder muscle, frozen, cut into 10-40-micro sections, and incubated for 1 hr at 25 degrees C in medium containing 0.025 M ATP, 0.0025 M lead nitrate, 0.05 M magnesium chloride, and 0.09 M sodium acetate buffer at pH 6.2, exhibited microcrystalline deposits in agranular endoplasmic reticulum and pinocytotic vesicles. Lead salt deposition was also noted in terminal cisternae of sarcoplasmic reticulum in skeletal muscle similarly treated, suggesting that the organelle systems in the two types of muscle cells subserve a common function.

A strand of cardiac muscle. Its ultrastructure and the electrophysiological implications of its geometry

The structure of a small strand of rabbit heart muscle fibers (trabecula carnea), 30-80 micro in diameter, has been examined with light and electron microscopy. By establishing a correlation between the appearance of regions of close fiber contact in light and electron microscopy, the extent and distribution of regions of close apposition of fibers has been evaluated in approximately 200 micro length of a strand. The distribution of possible regions of resistive coupling between fibers has been approximated by a model system of cables. The theoretical linear electrical properties of such a system have been analyzed and the implications of the results of this analysis are discussed. Since this preparation is to be used for correlated studies of the electrical, mechanical, and cytochemical properties of cardiac muscle, a comprehensive study of the morphology of this preparation has been made. The muscle fibers in it are distinguished from those of the rabbit papillary muscle, in that they have no triads and have a kind of mitochondrion not found in papillary muscle. No evidence of a transverse tubular system was found, but junctions of cisternae of the sarcoplasmic reticulum and the sarcolemma, peripheral couplings, were present. The electrophysiological implications of the absence of transverse tubules are discussed. The cisternae of the couplings showed periodic tubular extensions toward the sarcolemma. A regularly spaced array of Z line-like material was observed, suggesting a possible mechanism for sarcomere growth.

Cytochemistry of phosphatases of the sarcoplasmic reticulum. II. In situ localization of the Mg-dependent enzyme

The distribution of the Mg-dependent ATPase associated with a microsomal fraction of rabbit psoas muscle was studied histochemically and its localization in relation to the vesicles of the fraction and to the structure of intact fixed muscle was determined. Although enzyme activity was retained after fixation in hydroxyadipaldehyde and in glyoxal, it was lost after fixation in glutaraldehyde or after 4 hr fixation in formaldehyde. Activity was optimally demonstrated when incubations were conducted at 17 degrees C, in media containing 125 mM Trismaleate buffer, pH 7.5, 5 mM ATP, 4 mM MgCl(2), and 1 mM Pb(NO(3))(2). After such incubations, activity was present throughout the sarcoplasmic reticulum, but was absent from the T system. Activation by Na or K could not be demonstrated histochemically. However, the other biochemical properties of the enzyme in the isolated vesicles and in intact muscle were similar with respect to Mg dependence, substrate specificity, inhibition by Ca, N-ethyl maleimide, p-hydroxymercuribenzoate, and lack of inhibition by ouabain.

Effects of arginine deprivation, ultraviolet radiation, and x-radiation on cultured KB cells. A cytochemical and ultrastructural study

CULTURED KB CELLS (DERIVED FROM A HUMAN ORAL CARCINOMA) GROWN IN MONOLAYERS WERE INJURED BY ONE OF THREE AGENTS: starvation by arginine deprivation or treatment with high doses of either ultraviolet radiation or x-radiation. The different agents produced changes in nucleolar structure and varying accumulations of triglyceride and glycogen. All three agents produced an increase in number and size of lysosomes. These were studied in acid phosphatase preparations, viewed by both light and electron microscopy, and, occasionally, in vital dye, esterase, and aryl sulfatase preparations. Ultrastructurally, alterations in lysosomes suggested that "residual bodies" developed in a variety of ways, i.e., from the endoplasmic reticulum, multivesicular bodies, or autophagic vacuoles. Following all three agents the endoplasmic reticulum assumed the form of "rough" or "smooth" whorls, and, after two of the agents, arginine deprivation or ultraviolet radiation, it acquired cytochemically demonstrable acid phosphatase activity. Near connections between the endoplasmic reticulum and lysosomes raise the possibility that in KB cells, at least when injured, the endoplasmic reticulum is involved in the formation of lysosomes and the transport of acid phosphatase to them.