The ultrastructure of cat papillary muscle was studied with respect to the organization of the contractile material, the structure of the organelles, and the cell junctions . The morphological changes during prolonged work in vitro and some effects of fixation were assessed. The myofilaments are associated in a single coherent bundle extending throughout the fiber cross-section. The absence of discrete "myofibrils" in well preserved cardiac muscle is emphasized . The abundant mitochondria confined in clefts among the myofilaments often have slender prolongations, possibly related to changes in their number or their distribution as energy sources within the contractile mass . The large T tubules that penetrate ventricular cardiac muscle fibers at successive I bands are arranged in rows and are lined with a layer of protein-polysaccharide . Longitudinal connections between T tubules are common . The simple plexiform sarcoplasmic reticulum is continuous across the Z lines, and no circumferential "Z tubules" were identified . Specialized contacts between the reticulum and the sarcolemma are established on the T tubules and the cell periphery via subsarcolemmal saccules or cisterns . At cell junctions, a 20 A gap can be demonstrated between the apposed membranes in those areas commonly interpreted as sites of membrane fusion . In papillary muscles worked in vitro without added substrate, there is a marked depletion of both glycogen and lipid . No morphological evidence for preferential use of glycogen was found .Since the advent of the electron microscope, a great many significant papers have offered descriptions of limited aspects of the cytology of the ventricular cardiac muscle of various species (54,67,71,85,87, 99, 101, 108,110) . Considerably less information is available on the specific ultrastructural characteristics of the atrial muscle (28, 50) and, as yet, the nodal and specialized conduction tissues have received little detailed morphological investigation (51,93, 109) . This paper is the first of a series that will present a reasonably comprehensive description of the fine structure of the several regions of the cat myocardium . It is hoped that these papers on the special cytology of the heart will prove to be valuable morphological references for those investigators interested in correlation of the ultrastructure and the physiological and pharmacological properties of cardiac muscle .The slender ventricular papillary muscles of the cat heart have been extremely useful for physiological studies because they can be removed with minimal trauma and can be stimulated to contract for many hours in a bath of oxygenated 1 on

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Inflammatory skin diseases can be examined from many viewpoints. In this review, we consider three distinct cutaneous inflammatory diseases from the point of view of their major lesional dendritic cell (DC) subpopulations. The DC populations considered are Langerhans cells, myeloid DCs, and plasmacytoid DCs (pDCs), with specific attention to the presence and role of the inflammatory counterparts of these cells. From such a "dendritic cell-centric" focus, psoriasis, atopic dermatitis (AD), and cutaneous lupus erythematosus (CLE) are explored. In psoriasis, there is a specific population of myeloid "inflammatory" DCs that appears to play an important pathogenic role, while pDCs have been recently implicated in the initiation of psoriatic lesions. In AD, Langerhans cells may be important during initiation, while "inflammatory dendritic epidermal cells" (IDECs) appear to be abundant in lesional epidermis and dermis and contribute to maintenance of AD. These IDECs may actually be analogous to the myeloid inflammatory DCs found in the epidermal and dermal compartments of the skin in psoriasis, although they express distinct surface markers and induce different T cell polarities as a result of different cytokine milieu in which they develop. CLE has been recently characterized as a type I IFN-mediated disease, and pDCs are integral to the pathogenesis of this disease. Thus these DC subpopulations and their products will be reviewed in the context of these three cutaneous diseases, to provide clinico-pathophysiological correlations between the lesional DC, their products, and the skin diseases.

The ultrastructure of the cells specialized for contraction in the atrium and ventricle of young adult cats are compared . The cells specialized for conduction are not included . In addition to possessing distinctive atrial granules, the cells of the atrium are smaller in diameter (5-6 µ) than ventricular cells (10-12 µ) and have strikingly fewer T tubules . These latter differences are discussed in terms of their possible significance for the rate of conduction of the action potential . It is suggested that the very small number of T tubules in atrial cells may compensate for the small cell diameter, and thus permit rapid conduction of the action potential across the surface of the atrium . Coated dense vesicles found in association with the sarcoplasmic reticulum at the level of the Z line in ventricular muscle are more evident in atrial cells . In the virtual absence of T tubules in atrial cells, the subsarcolemmal cisternae of the sarcoplasmic reticulum are almost exclusively at the cell periphery . The ends of the cells and their processes in ventricular muscle are rectilinear with the interdigitated portions of the intercalated discs oriented transversely, whereas those of the atrium are often oblique to the myofilament axis . This difference may be related to the lower mechanical tension on atrial cells .

Nevi with architectural disorder and cytologic atypia of melanocytes (NAD), aka "dysplastic nevi," have varying degrees of histologic abnormalities, which can be considered on a spectrum of grades of atypia. Somewhat controversial and subjective criteria have been developed for grading of NAD into three categories "mild," "moderate," and "severe." Grading involves architectural and cytological features, which often correlate with each other. Architectural criteria were intraepidermal junctional extension beyond any dermal component, complex distortion of rete ridges, and dermal fibrosis. Cytological criteria were based on nuclear size, dispersion of chromatin, prominence of nucleoli, hyperchromasia and variation in nuclear staining. Few tests have been made of the relationship between specific grades of atypia and patient risk for melanoma. Retrospective review of pathology reports was performed on 20,275 nevi examined between 1989 and 1996. From the total, 6,275 were diagnosed as NAD, which were in 4,481 patients. These patients were divided into those whose worst NAD was mild (2,504), moderate (1,657), or severe (320). Review of accession data revealed that a personal history of melanoma was present in 5.7% of patients with mild, 8.1% with moderate, and 19.7% with severe atypia. The male/female ratios were similar in each group. In the three groups, the mean ages of men were similar and of women were similar, but the mean age of men tended to be 6 -11 yrs. older than women in each group. Family histories of melanoma were not considered. The odds ratio as a measure of association between NAD and personal history of melanoma, shows an odds ratio of 4.08 (2.91-5.7) for NAD-severe versus NAD mild, odds ratio 2.81 (2-3.95) for NAD-severe versus NADmoderate and odds ratio 1.45 (1.13-1.87) for NAD moderate versus NAD-mild. These data show that the probability of having personal history of melanoma, for any given NAD patient, correlates with the NAD grade. Likewise, the risk of melanoma is greater for persons who tend to make nevi with high grade histological atypia.