DNA synthesis of adult mammalian cardiac muscle cells in long-term culture

Adult rat cardiac ventricular muscle cells were isolated and cultured in monolayer for 30-45 days. Most of the cardiac muscle cells undergo external and internal structural alterations, resembling embryonic/neonatal cardiac muscle cells in culture (Nag and Cheng, 1981; Nag et al., 1983). These cultured cells underwent DNA synthesis and mitosis as revealed by autoradiography studies that involved the exposure of the cells to [3H]-thymidine for 24 hr prior to the termination of the culture at selected intervals. During the first week of culture, cardiac muscle cells showed less than 5% labeled cells. The labeling index of myocytes attained a peak in the second week of culture, exhibiting approximately 23% labeled cells. The labeling indices of cardiac muscle cells declined over the period of 30 days of culture. During the end of the incubation period, approximately 4% of the myocytes were labeled. When the extent of the total cell population involved in DNA synthesis was examined by exposing the cells to [3H]-thymidine continuously for long periods of time, it was observed that approximately 26% of the cardiac muscle cells regained the capacity for DNA synthesis during 1-10 days of culture. From day 1 to day 14, approximately 29% of the total muscle cell population was labeled. When the cells were exposed to the radioactive isotope continuously for 30 days, approximately 31% of the cells incorporated radioactive isotope, showing their capacity for DNA synthesis. Approximately 90% of the cardiac muscle cells in long-term culture contained more than one nucleus. The nuclei were often observed in multiples of two. Labeled mitotic apparatus was observed in cardiac myocytes, indicating the replication of DNA, followed by karyokinesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Factors controlling embryonic heart cell proliferation in serum-free synthetic media

Embryonic chick cardiac cell cultures, plated on collagen-coated dishes, containing serum-free synthetic media proliferate actively. The basic medium contained Ham's F12 nutrient mixture, fetuin, ascorbic acid, and bovine serum albumin. This medium was supplemented with various combinations of factors: endothelial cell growth supplement (ECGS), epidermal growth factor (EGF), insulin (I), transferrin (T), selenium (S), hydrocortisone, and thyroxine or supplemented alone. Basic medium supplemented with ECGS alone contributes to the highest final cell density among all other factors used in various combinations or alone. The final cell density of the control culture with 2% fetal bovine serum was higher than those of all experimental cultures and an additional control culture grown in the basic medium. Combinations of factors without ECGS do not promote significant cell proliferation. Thyroxine is required to induce optimal differentiation and contractility of cardiac myocytes in vitro. Fibronectin and laminin did not show any more influence than collagen did on the growth and maintenance of cardiac myocytes in serum-free media. The proportion of cardiac muscle cells in ECGS-containing media was higher than those in other experimental media and control media with the exception of ECGS and ITS-containing medium that showed lower proportion of cardiac myocytes than that of serum-containing medium on Days 3 and 5. The profiles of incorporation of [3H]thymidine into DNA of heart cells in experimental and control cultures showed a peak in incorporation values within the first week of culture and subsequently declined. Autoradiography studies revealed that cardiac myocytes in culture supplemented with ECGS alone attained a peak in labeling index on Day 1 with approximately 62% labeled cells. Subsequently, the labeling indices declined. Cardiac myocytes grown in media without ECGS showed significantly lower labeling indices than those in ECGS-containing media. This study has demonstrated the influence of ECGS, EGF and ITS in promoting the growth of cardiac myocytes and also in contributing to the maintenance of contractile cardiac myocytes in serum-free, long-term culture. The influence of ECGS on heart cell proliferation is considered to be superior to that of EGF and ITS.

Distribution of isomyosin in cultured cardiac myocytes as determined by monoclonal antibodies and adenosine triphosphatase activity

The distribution of isomyosin in cardiac muscle cells in culture has been investigated with monoclonal antibodies and Ca2+-activated myosin ATPase cytochemical staining. With immunofluorescent studies using monoclonal antibodies to isomyosins V1 and V3, the cardiac myocytes grown in a serum-free and thyroxine (T4)-free medium for 7 days contained a predominant population of cells which were strongly reactive to anti-V3 antibody. A small population of myocytes in this culture exhibited weak or no reaction to anti-V3 antibody. When cultures were exposed to anti-V1 antibody, the predominant cardiac myocyte population showed little or no reactivity to this antibody, whereas a small population of the myocytes were strongly reactive. The myosin ATPase staining reaction of the positive myocyte population was significantly less pronounced than that of the V3-negative population which showed a strong reaction. The staining pattern changed dramatically after exposure of cultured myocytes to thyroid hormone for 7 days. Most of the cells were found to react strongly with anti-V1 antibody, while some cells showed little reactivity and some were not stained at all. A small number of cardiac myocytes in this culture showed little or no reactivity to anti-V1 antibody but were strongly reactive to anti-V3 antibody. The predominant anti-V1-positive myocyte population exhibited strong myosin ATPase staining as compared to a smaller V3-positive myocyte population which showed very weak staining. The cytochemical results of ATPase staining in cardiac myocytes agreed well with ATPase activity as determined on pyrophosphate gels containing isomyosin derived from cultured cardiac myocytes with or without T4. This study has demonstrated that cultured myocytes contain a small population of muscle cells which is not responsive to thyroid hormone or to the lack of it.

Expression of myosin isoenzymes in cardiac-muscle cells in culture

Myosin isoenzyme profiles of rat and chicken embryonic cardiac myocytes were studied during differentiation and growth in vitro by native-gel electrophoresis and assay of Ca2+-activated ATPase. The electrophoretic pattern of myosin extracted from 18-day-embryonic-rat myocytes after 7 days in culture exhibits three isoenzyme bands, V1, V2 and V3, of which the slow-migrating V3 is predominant. This resembles the isoenzyme profiles from 18-20-day-embryonic ventricles in vivo. However, the isoenzyme profile of the 7-day-old culture differs from that of its counterpart in vivo, as well as from that of the young and adult rat ventricles, the last two containing the predominant fast-migrating component, V1. When embryonic cardiac myocytes were grown in vitro for 7 days in a medium containing a physiological concentration of L-thyroxine (T4), myosin isoenzyme profiles of these cells shifted to the adult form, with isoenzyme V1 predominating after day 4 of culture. The 7-day-old intact embryonic-chicken ventricles and isolated myocytes showed a single myosin isoenzyme band after 7 days of culture that resembles the pattern seen for the adult chicken. T4 had no effect on the electrophoretic mobility of this isoenzyme pattern. ATPase activity of isoenzyme V1 in cultured rat myocytes treated with T4 was comparable with that of V1 in the untreated adult heart. This study demonstrates that ATPase activity of the chicken myosin isoenzyme is significantly lower than that of isoenzyme V1, but is comparable with that of rat V3. This study shows that the expression of myosin isoenzyme profiles in cultured rat cardiac myocytes does not fully represent the situation in vivo. Physiological concentrations of T4 can modulate the predominant foetal-type isoenzyme V3 to the adult type V1 in cultured embryonic-rat cardiac myocytes within a brief period.

Evaluation of the genotoxicity of cresols using sister-chromatid exchange (SCE)

o-, m- and p-Cresols were evaluated in both an in vitro and in vivo SCE assay. Dose-dependent SCE increases were not observed in cultured human fibroblasts with any of the isomers at concentrations up to 8 mM. There was a small but significant increase in SCE frequency compared to control at 8 mM o-cresol. A significant decrease in cell-cycle progression as measured by average generation time (AGT), was seen for all isomers at a concentration of 8 mM. Furthermore, no increase in SCE frequencies was observed in bone marrow, alveolar macrophages, and regenerating liver cells of male DBA/2 mice treated with a single i.p. injection of either o-cresol (200 mg/kg), m-cresol (200 mg/kg), or p-cresol (75 mg/kg) 21.5 h prior to sacrifice.

A path probability model for sister-chromatid exchanges induced by alkylating agents

A path probability model is described for evaluation of sister-chromatid exchanges (SCEs) induced by alkylating agents following treatment of G1 cells at the beginning of the first or second cycles of BrdUrd incorporation, or during G1 corresponding to an exact cell-cycle interval preceding BrdUrd incorporation. Algebraic expressions are derived for calculations of expected induced SCE frequencies (over baseline levels) in second and third (reciprocal and nonreciprocal SCEs) division cells for the described treatment protocols. The derivations take into consideration: p, the probability of a specific lesion inducing an SCE; rn, the extent of repair within the nth post-treatment cycle; and X, the number of lesions induced. Expressions are also derived for expected ratios of single: twin exchanges in endoreduplicated or tetraploid cells.

Long-term cell culture of adult mammalian cardiac myocytes: electron microscopic and immunofluorescent analyses of myofibrillar structure

Adult rat heart was dissociated into a single-cell suspension by a retrograde perfusion technique with collagenase and hyaluronidase in Krebs-Ringer phosphate buffer. Long-term culture of these isolated single cardiac muscle cells was established for up to 45 days. Transmission electron microscopy and immunofluorescence analysis with monoclonal antibodies to cardiac myosin were used to examine sequentially the external and internal structural organization of the cardiac myocytes. Most of the cardiac myocytes exhibited prominent alterations in their external and internal structural organization during the first two weeks of culture. As they attached to the substrate and spread out, the myocytes assumed various shapes and sizes, with the exception of a few which maintained their original cylindrical shape. Electron microscopy of 2 to 4-day cultures revealed that most of the muscle cells contained disorganized myofibrils and surface blebs with enclosed mitochondria and myofilaments, which were eventually extruded from the cytoplasm. With progressive culture, the cardiac myocytes appeared to lose myofibrillar material; fewer myofilaments or sacromere fragments with interfibrillar mitochondria were observed in the sarcoplasm. Such cells resembled cultured embryonic or neonatal cardiac myocytes. However, some muscle cells retained closely packed, well organized myofibrils characteristic of freshly dissociated or in vivo cardiac myocytes. Immunofluorescence microscopy demonstrated that the cultured cardiac myocytes were strongly myosin positive throughout their morphological changes and subsequent maintenance in culture. Two patterns of fluorescence were observed in these cells in correlation with the fine structural evidence for myofibrillar distribution. One pattern exhibited bright fluorescence near the central region of the cell with a more weakly diffuse fluorescence throughout the cytoplasm; the other pattern was characterized by bright fluorescence throughout the sarcoplasm. Most of the myocytes retained their contractility throughout the culture period excepting the initial 24 to 48 h of cell attachment and flattening. These studies demonstrate the feasibility of maintaining contractile cardiac muscle cells from adult rats for at least 1 1/2 months in monolayer culture, although some variability in myofibrillar organization has been observed.

Persistence of ethyl carbamate-induced DNA damage in vivo as indicated by sister chromatid exchange analysis

Various treatment protocols were designed to investigate sister chromatid exchanges (SCEs) induced over successive posttreatment cell cycles in bone marrow and alveolar macrophage cells following treatment of C57BL/6J X DBA/2J F1 mice by i.p. injection of ethyl carbamate (3.3 mmol/kg). The same initial extent of alkylation in bone marrow and alveolar macrophages was suggested by identical SCE frequencies produced in both cell types by a one-cycle exposure protocol. The relatively lower responses in bone marrow cells by all other protocols may be a result of its faster mean population-cycling time. Second- and third-division cell SCE data produced by the various protocols indicate persistence of SCE-inducing lesions with no evidence of repair. In spite of the demonstrated lack of repair, first-cycle ethyl carbamate treatment was less effective than was second-cycle treatment in inducing SCEs. These results could not be attributed to selection of less-damaged cells over 2 cycles or to enhanced bromodeoxyuridine sensitivity in the second-cycle treatment protocol. It is speculated that the apparent cancellation of SCEs occurring over two successive cycles in the two-cycle exposure protocol may indicate the transient presence of ethyl carbamate-induced DNA interstrand cross-links. A possible mechanism of action of ethyl carbamate involving the formation of a transient cross-link and a persistent DNA monoadduct is postulated.

DNA synthesis in rat heart cells after injury and the regeneration of myocardia

The regenerative responses of the myocardia of post-natal rats of different age groups (1, 2, 3 and 4 weeks old) to an injury made by a clinical electricator were studied. DNA synthesis and the ultrastructural organization of the cardiac myocytes of the injured myocardia were examined for an evaluation of the potential for regeneration of the developing myocardia. The maximum labeling index of cardiac myocytes was observed in 1-week-old rats showing 8% labeled myocytes 3 days after injury as opposed to 3.2, 2.2 and 0.2% indices in 2-, 3- and 4-week-old rats respectively, 3 days after injury . In subsequent days after injury the labeling indices declined considerably in all age group hearts, and attained values less than 1% labeled myocytes 30 days after injury with the lowest labeling index in the oldest age group heart. When DNA synthesis in uninjured myocardial tissue adjacent to the injured tissue was examined, it was found to be significantly lower than it was in the injured tissue. However, both injured and adjacent uninjured tissue attained a peak in the labeling indices 3 days after injury, with the exception of 3- and 4-week-old uninjured tissue. The overall incorporation of 3H-thymidine into the DNA of heart cells as revealed by scintillation counts showed that the rate of incorporation of the isotope in younger hearts was significantly higher than in the older hearts. Non-muscle cells contributed significantly to the rise of scintillation counts in hearts of all age groups. Ultrastructural analyses of 1- to 4-week-old hearts showed that 24 hr after injury, injured areas of myocardia were heavily crowded with macrophages that surrounded damaged myocytes. Later on, fibroblasts and other non-muscle cells predominated the injury sites along with fibrous connective tissue. Scattered regenerating cardiac myocytes were frequently observed in the injury sites of 1- and 2-week-old hearts 3 days after injury. Myocytes were rare in the corresponding regions of 3- and 4-week-old hearts. Instead abundant non-muscle cells and fibrous connective tissue were predominant. In the fourth and final week of this study, the repaired areas of myocardia in 1- and 2-week-old rats contained more myocytes than those of the 3- and 4-week-old rats, and the repaired zone of the 1-week-old heart contained more myocytes than the repaired areas of the other age groups. These findings suggest that the mammalian myocardia possess an age-dependent potential for regeneration that involves the healing of injury sites with contractile and connective tissues.

Differentiation of fibre types in an extraocular muscle of the rat

Mammalian extraocular muscles possess greater variation in structural and physiological properties than any other muscle. The superior rectus muscle of the adult rat contains five morphological fibre types. The differentiation of the muscle into these fibre types in embryonic and postnatal rats were studied by light and electron microscopy, and the distribution of each developing fibre type with its distinctive features was mapped. The muscle of the 18-day embryos did not display the specific structural fibre types that were observed in the adult muscle. Newborn rat muscle exhibited some differentiation that included scattered small-diameter fibres with large myofibrils (fibre type 'B'). As development proceeded, another small-diameter fibre type with small myofibrils (fibre type 'A') appeared in the 6-day postnatal rat muscle. By the end of the first week of development neuromuscular junctions were in evidence in these two fibre types. Postsynaptic folds were rare in the large-fibril fibre, and folds were extensive in the small-fibril fibre. The medium- (fibre type 'C') and large-diameter (fibre type 'D') fibres were fully differentiated with small myofibrils and abundant sarcoplasmic reticulum (SR) by the second week of the development. SR was most abundant in the large-diameter fibre, which constituted the predominant global fibre type in the adult muscle. The postsynaptic folds in the neuromuscular junctions of these two fibre types were highly developed, although the innervation did not extend widely in the global region of the muscle. The last fibre type (fibre type 'E') was fully differentiated with the largest myofibrils, a small amount of SR, and simple neuromuscular junction by the third week of the postnatal development. The superior rectus muscle of the four-week-old rat was differentiated with all fibre types present in the adult muscle. During the third to sixth, and final, week of development, the other types described above exhibited extensive differentiation of characteristic structural features.

Organization of head injury service in Beijing

Beijing, the capital of the People's Republic of China, is a city with a population of over 10 million. The incidence of head injuries is increasing yearly and the government pays much attention to this social and medical problem. This is evidenced in both county and big city hospitals by the organization of neurosurgeons and general surgeons to serve the victim, by the training of some general surgeons in primary hospitals to handle emergency head injury care, and by the education of the citizens in accident prevention.

Comparison of sister chromatid exchange induction and known carcinogenic activities of vinyl and allyl carbamates

In vivo sister chromatid exchange (SCE) induction by vinyl and allyl carbamates was examined in alveolar macrophage, bone marrow, and regenerating liver cells of C57BL/6J x DBA/2J F1 mice. Allyl carbamate was effective in producing increases in SCE frequencies (relative to base-line SCE) over a dose range of 220 mumol/kg (approximately 2 times base line) to 2.2 mmol/kg (3 times base line). In general, alveolar macrophage and regenerating liver cells had higher responses, although not significantly, than did bone marrow. Vinyl carbamate produced significant increases in SCE frequencies over a dose range of 10 mumol/kg (2 times base line) to 75 mumol/kg (8 to 10 times base line). At the highest dose, SCE frequencies in extrahepatic tissues of hepatectomized mice were significantly higher than in intact mice and, within hepatectomized mice, alveolar macrophage and regenerating liver cell responses were greater than were bone marrow responses. Vinyl carbamate was approximately 30 times as potent a SCE inducer than we reported previously for ethyl carbamate. To date, our studies of six different carbamate esters have indicated a striking similarity in relative potencies for SCE induction and their known tumorigenic potencies.U

Ribonucleic acid metabolism in rat liver during long-term adaptation to malnutrition

Ornithine decarboxylase (ODC) and nucleolar DNA-dependent RNA polymerase (RNA polymerase I) activities increased in the liver of young adult male rats fed a 6% casein diet (malnourished) for 1 week when compared with rats fed a 25% casein diet (control). ODC activity increased progressively and reached a peak after 3 weeks of malnutrition and then decreased to control values by 5 weeks. RNA polymerase I reached peak activity 1 week after malnutrition was imposed, decreasing thereafter to control values by 3 weeks. At 4 and 5 weeks, RNA polymerase I activity in malnourished animals was lower than control. Nucleoplasmic DNA-dependent RNA polymerase activity remained unchanged in the first 2 weeks of malnutrition and decreased thereafter to values significantly lower than control. The data confirm our previous observations of cyclical changes during prolonged malnutrition and suggests a process of "biochemical adaptation" to malnutrition in which the organism enhances essential metabolic processes to maintain cellular homeostasis to the detriment of less essential functions like systemic growth.

Purification and physicochemical characterization of human alpha 2-HS-glycoprotein

A large-scale purification method for alpha 2 HS-glycoprotein from normal human pooled serum is presented. 130 mg of alpha 2 HS was obtained from 21 of normal serum and the yield was 13.6%. Charge heterogeneity on isoelectrofocusing of this protein is mainly due to sialic acid. By the measurement of the circular dichroism spectrum, the alpha-helix content was calculated as 11% and the beta-structure content was calculated as 21 to 33%. alpha 2HS consists of a single polypeptide chain (Mr 49,000) of which the N-terminal amino acid is alanine. The N-terminal sequence of 31 amino acids contains 19 hydrophobic residues.

Potency of some carbamates as multiple tissue sister chromatid exchange inducers and comparison with known carcinogenic activities

The ethyl, ethyl N-hydroxy, isopropyl, and methyl esters of carbamic acid were examined for their abilities to induce sister chromatid exchanges (SCEs) in alveolar macrophages, bone marrow, and regenerating liver cells of C57BL/6J X DBA/2J F1 mice. The relative potencies in inducing SCE, ethyl greater than ethyl N-hydroxy- greater than isopropyl, paralleled previously described activities for induction of lung adenomas in strain A mice. The noncarcinogenic methyl carbamate was inactive in the SCE assay. Relative to bone marrow, regenerating liver and alveolar macrophage cells demonstrated increased susceptibility to carbamate-induced SCE. Of all carbamates studied, only the directly active compound, ethyl N-hydroxycarbamate, produced distinctly different responses in extrahepatic tissues of hepatectomized and intact mice. In intact mice, SCE levels induced by ethyl carbamate in bone marrow and alveolar macrophage cells were not significantly different whether assay followed the last of 12 (three times weekly) serial injections of 2.2 mmol/kg each or after a single injection of 2.2 mmol/kg. Linear regression relationships of log ethyl carbamate versus log SCE or log adenoma response were found to be parallel with the two assays having similar sensitivities.

Multicellular in vivo sister-chromatid exchanges induced by urethane

Following urethane inhalation exposure, clear dose--response relationships were apparent in all cell types examined in hepatectomized and intact mice. At concentrations of 0.1 mg/l and higher, induced SCE frequencies were linearly related to log urethane concentrations. No significant differences in SCE response between like cell types of hepatectomized and intact mice were apparent. In hepatectomized mice, there was no significant difference in the SCE response of regenerating liver and alveolar macrophage cells. However, bone-marrow response was significantly lower (p = 0.01). Likewise, in intact mice bone marrow response was significantly lower than in alveolar macrophages (p = 0.01). Inhalation and intravenous infusions of the same total dose of urethane (193 mg/kg) administered over a 4-h period produced comparable SCE responses in all cell types. However, a single intraperitoneal injection of 193 mg/kg just prior to BrdU infusion produced significantly higher SCE frequencies in bone marrow (alpha = 0.01), and alveolar macrophages (alpha = 0.05) of intact mice than did the equivalent inhalation dose. Intraperitoneal injections produced similar results in 2-month-old mice as in 4-month-old mice. However, regardless of the route of administration SCE frequencies in regenerating liver and/or alveolar macrophages were significantly higher than in bone marrow.

Adult mammalian cardiac muscle cells in culture

Adult rat cardiac muscle cells were isolated from the ventricle by a retrograde perfusion technique through the aorta (Nag and Zak, 1979). These single, isolated cardiac muscle cells were cultured for 4 weeks. Throughout the culture period, a small number of muscle cells retained their cylindrical shape, while the rest exhibited alterations in shape and size assuming a flattened body of irregular shape with pseudopodia-like processes and thereby resembling embryonic/neonatal cardiac muscle cells in culture. Transmission electron microscopy revealed that the cylindrical muscle cells contained compactly arranged myofibrils and cellular organelles, similar to those of freshly isolated and in vivo cells. A few irregularly shaped cardiac muscle cells were similar to the cylindrical cells in their internal structural organization. Most of the irregular cells exhibited less myofibrillar content than that of the freshly dissociated and in vivo cells. Myofibrils in the irregular cells were widely spaced and myofilament of some of the myofibrils were loosely bunched. In addition, scattered patches of myofibrils and free myofilaments were observed in many of these cells. The internal structural organization of these irregularly shaped cardiac muscle cells closely resembled the embryonic and neonatal cardiac muscle cells in vitro and in vivo. Most of the muscle cells in culture continued to contract spontaneously, and electron microscope studies clearly indicated that they underwent dedifferentiation. Autoradiography studies demonstrated that the cylindrical and irregularly shaped cardiac muscle cells underwent DNA synthesis and cell division in culture.

Coaggregation and formation of a joint myocardial tissue by embryonic mammalian and avian heart cells

Intercellular adhesion and tissue reconstruction from homologous dissociated embryonic cells from two species were studied. Dissociated 12-day-old embryonic rat heart cells and 50-h-old embryonic chick heart cells were labeled with tritiated thymidine and allowed to aggregate in Erlenmeyer flasks during rotation culture on a gyratory water-bath shaker. The cultures were continued for 72 h. Cell aggregates were examined microscopically for evidence of contractility and subsequently processed at intervals between 1 and 72 h for transmission electron microscopic autoradiography. Rat and chick hearts used in this study appeared comparable in their stage of development and cellular composition. With the exception of mature blood cells and some fibroblastic non-muscle cells, all chick cardiac muscle cells were labeled with tritiated thymidine. As the cultures continued, aggregates increased in size by continuous accretion of cells and joining of small clusters. The cells within these mixed aggregates exhibited synchronous contractility from 1 h until the cultures were terminated. Most of the aggregation in both control and mixed aggregates was completed within 24 h. Control aggregates consisted of cells from a single species, either chick or rat. Approximately 18% of labeled chick cardiac muscle cells established intercellular contacts and junctions with unlabeled rat cardiac muscle cells after 6 h of culture. This increased to 72% after 72 h in culture. The junctions observed between chick and rat cardiac muscle cells were desmosomes and hemidesmosomes. Approximately 13% of the cardiac muscle cells of one species either chick or rat were found scattered within clusters which contained 15% of the cells from the other species after 72 h of culture. These scattered cells did not form junctions with monospecific cell groups. The implications of these intercellular adhesions between the same and different species are discussed, bearing two hypothesis in mind: (1) Moscona and collaborators, (2) Burdick and Steinberg. This study suggests that cellular as well as species identity plays an important role in the determination of intercellular adhesion among the embryonic cells from different species.

Intercellular adhesion: coconstruction of contractile heart tissue by cells of different species

Dissociated embryonic rat myocardial cells and chick myocardial cells labeled with radioactive isotope coaggregate and establish intercellular junctions. These bispecific cells reconstruct synchronously beating myocardial tissue within 24 hours of culture.

Irradiation of the surgeon during pinning of femoral fractures

The intensity of scattered radiation in both a forward and a backward direction from a portable fluoroscope during pinning of the neck of the femur was measured by experiments on a cadaver. The intensity decreased rapidly with increasing distance from the flare of the greater trochanter. Hazard to the surgeon's hands from scattered radiation can be greatly reduced by positioning the C-arm of the fluoroscope so that the x-ray beam is directed laterally.

Studies of adult amphibian heart cells in vitro: DNA synthesis and mitosis

The ventricle of the adult newt heart was excised and cut into several pieces of approximately 0.5-1.0 mm. These heart pieces were then cultured for 60 days at 25 degrees C in a modified Leibovitz medium (L-15). Approximately 37% of the explants were attached to the substrate and more than 33% of the attached explants and approximately 15% of the unattached explants established pulsation rates which ranged 3-67 beats/min. The explants were labeled with 1 muCi/ml of 3H-thymidine for 24 hr at 7, 15, 21, 30, 45 and 60 days of culture initiation, and processed for electron microscopic autoradiography. The examination of the autoradiograms revealed that as the culture continued, the cardiac muscle cells altered their morphology, resembling embryonic cardiac muscle cells. These altered muscle cells were termed dedifferentiated cardiac muscle cells. The number of these dedifferentiated cells increased over the period of culture, showing 10.3-94% dedifferentiated cells after 7-60 days of culture respectively. DNA synthesis and mitosis were observed in the dedifferentiated cardiac muscle cells, apart from the non-muscle cells. The quantitation of the autoradiograms revealed that the number of labeled nuclei in the cardiac muscle cells gradually increased over the period of culture, and a maximum number of labeled cardiac muscle cells (30%) was observed in the third week. The peak was followed by a decline in the eighth week which exhibited 1.5% labeled cardiac muscle cells. The trend of mitosis was similar to that of DNA synthesis. The maximum number of mitotic figures (9%) was observed in the third week of culture, which was followed by a decline and finally absent in the eight week. The cardiac non-muscle cells, mostly fibroblasts and endothelial cells, also showed incorporation of 3H-thymidine in their nuclei. The number of labeled non-muscle cells nuclei and the mitotic index were highest (61 and 15% respectively) in the first week of culture, but then they decreased gradually over the eight-week period in culture. This study provides evidence for the first time that the adult amphibian cardiac myocytes can undergo DNA synthesis and mitosis when explanted and cultured. The significance of this cell replication is discussed.

DNA synthesis and mitosis in adult amphibian cardiac muscle cells in vitro

High-resolution autoradiography and fine structural analysis of adult newt heart tissue in long-term culture revealed that tritiated thymidine was concentrated in the nuclei of dedifferentiated myocardial cells. Mitotic chromosomes were observed in some of these cells. This demonstrates that adult amphibian myocardial cells in vitro are capable of DNA synthesis and mitosis.

Organ culture of adult amphibian heart: a fine structural analysis

Pieces of hearts from adult newts were cultured up to 2 months. Within 7 days of culture, approximately 37% of the cardiac explants were attached to the substrate and more than 33% of the attached explants and approximately 15% of the unattached explants established pulsation rates ranging from 3 to 67 beats/min. The control and cultured explants were processed at weekly intervals for electron microscopy. The diameter of the control cardiac muscle cells ranged approximately 3-5 micron. The cell surface was provided with microvilli. The intercellular spaces ranged approximately 150-500 A. The intercalated discs lacked the step-like courses observed in the mammalian cardiac muscle. Sarcoplasmic reticulum was scanty. Desmosomal-dense materials were frequently continuous with the Z-bands of both control and cultured cardiac muscle cells. The transverse tubular system and gap junction were absent in newt ventricles. The functional implications of these characterisitics are discussed. At the end of 1 week of culture, the surfaces of the explants were covered by one or more layers of non-muscle cells, and the core of the explants consisted mostly of cardiac muscle cells. In a few cardiac muscle cells the myofibrillar organization was disrupted, resulting in the distribution of scattered patches of myofibrils and free myofilaments in the sarcoplasm. A small number of intact muscle cells contained a considerable number of dense granules in the sarcoplasm. At 15 days in culture, a large number of muscle cells showed structural features reminiscent of embryonic cardiac muscle cells. These cells possessed patches of myofibrils, scattered myofilaments and scanty sarcoplasmic reticulum along with other cellular organelles and inclusions. Several of these altered cardiac muscle cells contained mitotic figures. The cardiac explants maintained the initial beating rate until the end of 2 months of culture, except for the 11% of the explants which stopped beating. By 3-4 weeks in culture, most of the cardiac muscle cells possessed the altered cell morphology mentioned above. The explants after 60 days in culture became more flattened than the earlier explants. The intact cardiac muscle cells were rare, and the cores of the explants were mostly occupied by the altered cardiac muscle cells. It is evident from our studies that the cardiac muscle cells have undergone dedifferentiation in long-term culture, and that this dedifferentiation process has yet had no effect in the maintenance of contractility of the explants. Furthermore, these dedifferentiated cardiac muscle cells are capable of DNA synthesis and mitosis.

The safety of local anesthesia and outpatient treatment: a controlled study of induced abortion by vacuum aspiration

The safety of early vacuum aspiration performed as an outpatient procedure using local anesthesia was examined in a controlled study sponsored by the World Health Organization and undertaken in two centers in Yugoslavia and Singapore. The sample consisted of healthy women whose pregnancies were between 7 and 12 weeks in duration. Follow-up four weeks after abortion was nearly 100 percent in both centers. No important differences in complication rates were found between the different types of services and anesthesia, even though overall complication rates differed markedly between centers. Overnight postabortion observation was not associated with any decrease in complications.

Complications following induced abortion by vacuum aspiration: patient characteristics and procedures

Complications following early induced abortion by vacuum aspiration were examined in a controlled study. Data were collected on healthy women 7--12 weeks pregnant at the time of abortion. No association was found between complication rates and age, marital status, or parity. However, women in their first pregnancies and those who had experienced an induced or spontaneous abortion in their previous pregnancy had a higher rate of complications following the current induced abortion.

Distribution of antibodies to the troponin complex, troponin-C and troponin-I in chicken skeletal muscle as determined by a simplified method for immuno-electron microscopy

Antisera against the troponin complex, troponin-C and troponin-I have been utilized to locate these proteins in normal, adult chicken skeletal muscle and in filaments prepared from chicken acetone dried powder. The antisera had been previously characterized by immunochemical methods and were employed to ascertain the distribution of the proteins by a simple method for immuno-electron microscopy. Glycerinated chicken breast muscle was treated with the antisera, unreacted antibody was washed from the muscle, and a goat anti-rabbit gamma-globulin was added to enhance the electron density of the antigen-antibody complexes. A periodic distribution of anti-troponin-C at a mean interval of 389 A was observed along the thin filaments in the sectioned tissue. Anti-troponin-I was deposited every 399 A (P less than 0-01). Thin filaments were prepared from acetone dried powder and reacted with the antisera. The anti-troponin-C was located every 389 A; anti-troponin-I, every 399 A (P less than 0-01). Our technique for immuno-electron microscopy is compared with that used by others, and the significance of the findings is discussed.

Optokinetic nystagmus during selective retinal stimulation

Nystagmic eye movements in response to selective optokinetic stimulation of different parts of the retina were studied in normal human subjects by two methods: 1. a digital computer controlled by the eye movement signal was used to generate an optokinetic display which stimulated only the peripheral retina, simulating a central scotoma, and 2. a single dot of 0.6 degrees in diameter was used as the stimulus during maintained forward gaze. The results show that stimulation of the central or peripheral retina alone can produce optokinetic nystagmus in man, and that essentially the same type of nystagmus is produced in both cases. The slow phase velocity of nystagmus evoked from the peripheral retina falls off rapidly with distance from the fovea but can be facilitated by attention. Results are compared with other findings and a possible explanation is offered for the observed variation in slow phase speed which occurs during constant velocity optokinetic stimulation.