The effects of mechanical stability on the macromolecules of the connective tissue matrices produced during fracture healing. I. The collagens

Summary The distribution of types I, II, III, V and IX collagens in healing fractures of the rabbit tibia has been demonstrated by immunofluorescent techniques. It has also been shown that the mechanical stability of the healing fracture affects both the distribution and types of the collagens present.The initial fibrous matrix contains types III and V collagens; type I collagen was only located in this matrix if unfixed tissue was used. In mechanically stable fractures, cancellous bone forms over the entire periosteal surface by 5–7 days; type I collagen is laid down within the previous fibrous matrix. The trabeculae are heterogeneous in their collagen content. The cavities contain a matrix of types III and V collagens. Small nodules of cartilage may be present between 7 and 14 days; these contain types II and IX collagens.In mechanically unstable fractures, cancellous bone is initially formed away from the fracture gap. The fibrous tissue over the gap is replaced by cartilage; types II and IX collagens are laid down on the pre-existing fibrous matrix. The cartilage is replaced by endochondral ossification. At the ossification front, type I collagen is found around the chondrocyte lacunae of the spicules of cartilage. The new trabeculae contain a core of cartilage which is surrounded by a bone matrix of types I and V collagens.The fracture gaps are invaded by fibrous tissue, which contain types III and V collagens. This is later replaced by cancellous bone.     

The origin of 45,X males.

Maleness in association with the karyotype 45,X is a very rare and hitherto unexplained condition previously described in only four or five patients. This study was carried out to determine whether such males might actually possess Y-chromosomal material. Of the two 45,X males studied, one was found to be a low-grade mosaic with a 46,XY karyotype in less than 3% of fibroblasts; all lymphocytes karyotyped were 45,X. Fibroblast DNA from this individual was found to contain Y-specific repeated sequences in 1%-3% the amount observed in the father, consistent with mosaicism for a 46,XY cell line. No Y-specific repeated sequences were detected in the other patient, in whom all mitoses were 45,X. In neither patient were there detectable amounts of any of the single-copy Y-specific DNA sequences for which we tested. Studies of Xg blood groups and of X-linked restriction fragment length polymorphisms indicated that the single X chromosome was of maternal origin in both 45,X male probands. In contrast to the situation in XX males, we can exclude paternal X-Y interchange as the etiology in the cases described here. Our findings are compatible with mosaicism being the explanation of at least some "45,X" males.     

A deletion map of the human Y chromosome based on DNA hybridization.

The genomes of 27 individuals (19 XX males, two XX hermaphrodites, and six persons with microscopically detectable anomalies of the Y chromosome) were analyzed by hybridization for the presence or absence of 23 Y-specific DNA restriction fragments. Y-specific DNA was detected in 12 of the XX males and in all six individuals with microscopic anomalies. The results are consistent with each of these individuals carrying a single contiguous portion of the Y chromosome; that is, the results suggest a deletion map of the Y chromosome, in which each of the 23 Y-specific restriction fragments tested can be assigned to one of seven intervals. We have established the polarity of this map with respect to the long and short arms of the Y chromosome. On the short arm, there is a large cluster of sequences homologous to the X chromosome. The testis determinant(s) map to one of the intervals on the short arm.     

Rat heart gap junctions as disulfide-bonded connexon multimers: Their depolymerization and solubilization in deoxycholate

Summary Unproteolyzed gap junctions isolated from rat heart and liver were analyzed for the presence of inter-subunit disulfide bonds by sodium dodecylsulfate polyacrylamide gel electrophoresis. Rat cardiac junctions contained multiple disulfide bonds connecting theM _r 47,000 subunits of the same connexon and of different connexons. Inter-subunit disulfide bonds were absent in liver junctions. Unproteolyzed rat heart gap junctions were resistant to deoxycholate in their oxidized state, but dissolved readily in the detergent when the disulfide bonds were cleaved with -mercaptoethanol. Disulfide bonding in proteolyzed cardiac junctions was limited to pairs ofM _r 29,500 subunits. These junctions were not soluble in deoxycholate even in the presence of -mercaptoethanol. These results show that heart and liver junctions differ in their quarternary organization.     

Sexually dimorphic mechanosensitive swimmeret sensilla affect abdominal posture in the lobster

The sensilla on the male and female second swimmerets are sexually dimorphic. Female swimmerets contain many long "smooth hairs" (long simple setae) on the coxa and rami. The endopodite of the male swimmeret has an accessory lobe covered with short "bristly spines" (serrate setae). In both sexes the swimmeret rami are lined by "feathered hairs" (plumose setae). The influence of mechanosensory stimulation of these sensilla upon abdominal tonic motor activity was analyzed in an in vitro swimmeret-nerve cord preparation. Movement of several clusters of smooth hairs produced an abdominal extension program by exciting the flexor inhibitor f5, inhibiting the flexor excitors, and activating several extensors. Stimulation of the male bristly spines excited the medium-sized flexor excitors f3 and f4. In both sexes the feathered hairs did not generate any response to mechanical stimulation. We infer that in nongravid females the smooth hairs are involved in receiving mechanosensitive cues to support abdominal extension. Bristly spines may contribute to postural adjustments that assist mating. The long latencies of these responses and their propagation to adjacent ganglia suggest that they are mediated by postural interneurons rather than by direct afferent terminations on postural motoneurons.     

Separation of cardiac plasmalemma into cell surface and T-tubular components. Distribution of saxitoxin- and nitrendipine-binding sites

To compare surface sarcolemmal with T-tubular distributions of [3H]saxitoxin (STX)- and [3H]nitrendipine (NTD)-binding sites, we centrifuged membrane vesicles from sheep and bovine ventricles on a 10-40% linear sucrose gradient from which fractions were assayed for STX and NTD binding; for markers of surface sarcolemma (ouabain-sensitive Na,K-ATPase activity, [3H]quinuclidinyl benzilate binding); and for markers of junctional sarcoplasmic reticulum known to be preferentially associated with T-tubules (ryanodine-sensitive Ca2+ uptake, calsequestrin, an Mr 300,000 putative phosphorylatable "foot" protein, and electron microscopically visible junctional sarcoplasmic reticulum-plasmalemma complexes). We identified three distinct peaks in the sucrose gradient, each characterized by significant high and low affinity STX- and high affinity NTD-binding: Peak I (approximately 19% sucrose), highly enriched in surface sarcolemma; Peak III (approximately 36% sucrose), enriched in junctional sarcoplasmic reticulum markers and hence in junctional sarcoplasmic reticulum complexes with T-tubule; and Peak II (approximately 27% sucrose), showing greatest specific STX binding and only moderate NTD binding, enriched in T-tubular membrane, unassociated with junctional sarcoplasmic reticulum. For ventricular myocytes, the ratio NTD sites/STX sites was 2.5 for surface sarcolemma, but only approximately 1.0 for T-tubules. Unlike data published for mammalian skeletal muscle, sheep and beef cardiac NTD receptors were not significantly more concentrated in T-tubular than in surface plasmalemma.     

Circadian rhythms in the electroretinogram of the cockroach

Circadian regulation of the amplitude of the electroretinogram (ERG) of the cockroach Leucophaea maderae was investigated. Two components of the ERG exhibited circadian rhythms in amplitude. Interestingly, the peak amplitudes for the two rhythms were approximately 12 hr out of phase. The dominant corneal negative potential (the "sustained component") exhibited maximum amplitude during the subjective night. A second corneal negative potential (the "off-transient") was at a maximum during the subjective day. Intensity-response curves of the sustained component were measured at both the peak and trough of the rhythm. The results showed that the circadian rhythm in amplitude reflected a sensitivity change equivalent to 0.2-0.6 log unit of intensity. An effort was also made to identify the anatomical locus of the pacemaking oscillator for the ERG rhythm in a series of lesion experiments. Neural isolation of the optic lobe from the midbrain by bisection of the optic lobe proximal to the distal edge of the lobula had no effect on the circadian rhythm of ERG amplitude. Bisection of the optic lobe distal to the lobula abolished the ERG amplitude rhythm. These results suggest that the pacemaker is located in the optic lobe near the lobula; that its motion continues in the absence of neural connections with the rest of the nervous system; and that its regulation of ERG amplitude depends on neural pathways in the optic lobe.     

Delayed-onset synergism between leukotriene B4 and prostaglandin E2 in human skin

The time-course of cutaneous inflammatory responses to LTB₄ and PGE₂ both alone and in combination has been studied in 10 healthy volunteers. LTB₄ induced a transient wheal and flare response in some subjects, maximal at 15 minutes and succeeded by an erythematous, indurated lesion at 2–4 hours. PGE₂ elicited a wheal and erythema response which resolved within 1–2 hours. Combination of LTB₄ and PGE₂ produced acute wheal and erythema responses which did not differ significantly from the summation of responses to the individual constituents of the mixture or from responses to a two-fold increase in the concentration of either component. Wheal and erythema responses persisted, however, with significant potentiation of responses 4 hours after injection. As both leukotrienes and prostaglandins are generated in acute allergic reactions, the effects of these mediators in combination could contribute to persisting and late-onset responses to allergen, in both the skin and lung. In particular, sustained responses to the combination of LTB₄ and PGE₂ might be important in the pathogenesis of inflammatory skin diseases such as psoriasis.