Candidate mechanical stimuli for hypertrophy during volume overload.

A myocyte system that senses and responds to mechanical inputs might be activated by any number of features of the time-varying length or force signals experienced by the myocytes. We therefore characterized left ventricular volume and wall stress signals during early volume overload with high spatial and temporal resolution. Left ventricular pressure and volume were measured in open-chest isoflurane-anesthetized male Sprague-Dawley rats 4 and 7 days after surgical creation of an infrarenal arteriovenous fistula or sham operation. Mean wall stresses were calculated by using a simple thick-walled ellipsoidal model. Consistent with previous reports, this surgical model produced a 66% increase in cardiac output and a 10% increase in left ventricular mass by day 7. A number of features of the time-varying volume signal (maximum, mean, amplitude, rates of rise and fall) were significantly altered during early volume overload, whereas many other proposed hypertrophic stimuli, including peak systolic wall stress and diastolic strain, were not. Treating hemodynamic variables more generally as time-varying signals allowed us to identify a wider range of candidate mechanical stimuli for hypertrophy (including some not previously proposed in the literature) than focusing on standard time points in the cardiac cycle. We conclude that features of the time-varying ventricular volume signal and related local deformations may drive hypertrophy during volume overload and propose that those features of the volume signal that also change during pressure overload might be the most interesting candidates for further exploration.     

Purification of bovine liver histidyl-tRNA synthetase, the Jo-1 antigen of polymyositis: size of the whole enzyme and its characteristic proteolytic fragments

We have recently reported the marked increase in frequency which can be achieved in the detection of the anti-Jo-1 antibody of polymyositis in serum samples by replacing commercial mixtures of cytoplasmic and nuclear antigens with the purified antigen, histidyl-tRNA synthetase. The present paper describes a method for purifying this antigen and an investigation of its size. Molecular masses previously reported for the enzyme have varied from 85-154 kDa and subunit molecular masses varying from 40-77 kDa have been observed. Several of these fragments are of sizes similar to those of a number of other autoantigens commonly observed in connective tissue diseases. Since the clinical identification of these autoantigens often relies exclusively on size determination by Western blotting, we have characterized the commonly occurring fragments of histidyl-tRNA synthetase lest they confuse such identification. It is concluded that histidyl-tRNA synthetase, like many other aminoacyl-tRNA synthetases, is subject to severe proteolysis during extraction procedures. Several characteristic fragments (Mr = 80, 75, 61, 55, 50 and 45 kDa) result, a finding that provides a satisfactory explanation of the various values previously reported. The intact bovine enzyme is a dimer of molecular mass close to 160 kDa.     

COMMENTARY ON ZOHAR'S “PROSPECTS FOR‘GENETIC THERAPY’- CAN A PERSON BENEFIT FROM BEING ALTERED?”

In his paper on the effects of Prenatal Genetic Intervention (PGI) on personal identity, Noam Zohar comes to a conclusion about genetic makeup and the uses of gene therapy quite different from the one I reach in another piece in this issue. Zohar's argument rests on the contention that personal identity changes with alteration of the genome, following what I have identified as the "constitutive" view. To see that this is the pillar supporting the weight of his argument, consider the following. Questions of identity aside, how can it be that altering the genome of children suffering from Lesch-Nyhan syndrome or Tay-Sachs disease so that they now produce the enzyme that they formerly lacked does not benefit them? Clearly, if their identities were not changed, such individuals would in fact realize great benefit from PGI, since the devastating bad effects of the genetic flaw would be avoided. Such a change would certainly make the altered individuals better off, that is, it would benefit them. On this, Zohar and I do not disagree. Persistence of identity through such genetic change is the sticking point.     

Biotype-specific expression of dsRNA in the sweetpotato whitefly

This study was conducted to evaluate the effect of two different biotypes of the sweetpotato whitefly,Bemisia tabaci (Gennadius), on the induction of squash silverleaf (SSL), and to determine if double-stranded RNA (dsRNA) occurs in geographically remote populations of the two biotypes. Recently collected B-biotype whiteflies from Florida, Arizona, Mississippi, and Texas (SPW-B) all contained a 7.0 kb dsRNA molecule. Kb dsRNA molecule. Laboratory colonies of A-biotype whiteflies that were originally collected in 1981 from cotton in Arizona and California did not contain the 7.0 Kb dsRNA. When the two biotypes were compared only the SPW-B induced rapid onset, grade 5, SSL. DsRNA similar to that found in adult SPW-B was concentrated in whitefly nymphs, but host plant leaf tissue did not contain any consistent dsRNA molecules. SPW-A only induced low-grade SSL and progeny of SPW-A that were fed on pumpkin plants displaying SSL did not acquire the ability to express dsRNA or induce SSL. Our data suggest that dsRNA is not directly involved in the induction of SSL and that SSL is a host-specific response, to a feeding injury induced by B-biotype whiteflies. The origin and source of the 7.0 Kb dsRNA molecule remains enigmatic but its expression is constant in the whitefly biotype that is responsible for the induction of SSL and several other plant disorders in the U.S.     

Mutations inside but not outside the peptide binding cleft of the H-2 Ld molecule affects CTL recognition and binding of the nucleoprotein peptide from the lymphocytic chroriomeningitis

In order to investigate the role of residues inside and outside the peptide binding cleft of the L² molecule in peptide presentation to cytotoxic T lymphocytes (CTL), we constructed a series of point mutations in the L ^d gene. We determined the effects of the mutations in the L^d molecule on the binding and recognition of an L^d-restricted CTL epitope derived from the nucleoprotein (NP) of the lymphocytic phoriomeningitis virus (LCMV). Each of the mutations within the L^d peptide binding cleft resulted in a complete loss of CTL recognition. Addition of the LCMV NP peptide to cells expressing these mutants did not increase surface L^d expression, suggesting that the mutations altered peptide binding. Mutations involving pockets D and E within the cleft affected LCMV peptide binding and recognition as drastically as those in pocket B, which was predicted to interact with a main anchor residue of the peptide. In striking contrast, the mutations located outside the cleft did not change either recognition or binding. These results demonstrate that the L^d residues in the peptide binding cleft are the main determinants dictating LCMV NP peptide binding, and that the residues in each of the pockets within the cleft play a role in this interaction. Surprisingly, one mutation outside the peptide binding cleft, T92S, abrogated CTL lysis of target cells treated with the LCMV NP peptide, but not virus-infected cells. These data show that this mutation selectively altered the presentation of the LCMV NP peptide introduced to the cell exogenously, but not endogenously. This implies that the pathway by which peptides associate with class I molecules within the cell differs from that of exogenous peptide binding.     

PrP in pathology and pathogenesis in scrapie-infected mice

PrP accumulation in the brains of mice infected with scrapie takes several different forms: amyloid plaques, widespread accumulation in neuropile, and perineuronal deposits. PrP is also sometimes detected within microglia and in or around astrocytes. There are dramatic and reproducible differences between scrapie strains in the relative prominence of these changes and their distribution in the brain. Depending on the scrapie strain, PrP pathology is targeted precisely to particular brain areas, often showing a clear association with identifiable groups of neurons. These results suggest that PrP changes are primarily associated with neurons, and that different scrapie strains recognize and selectively replicate in different populations of neurons. Immunostaining at the ultrastructural level demonstrates an association of PrP with neurite plasmalemma, around amyloid plaques, and in areas of widespread neuropile and perineuronal accumulation. It is probable that PrP is encoded by theSinc gene, which controls the incubation period of scrapie in mice. Studies using the intraocular infection route show that theSinc gene controls the onset rather than the rate of replication, suggesting that PrP may be involved in cell-to-cell spread of infection. The accumulation of PrP at the surface of neurons is consistent with such a role.     

Studies with a human plasma-derived immunosuppressive,anti-lymphoma factor

Summary A low-molecular-weight (1,400) factor isolated from a human plasma -globulin concentrate by acid-salt dissociation and ultrafiltration inhibits proliferation of mitogen-stimulated T cells and L1210 leukemia cells. The factor (UM05R) inhibits DNA, RNA, and protein synthesis in sensitive cells, acts in G1 of the cell cycle, and appears to suppress mitogen-responsive T cells without an accessory cell requirement. UM05R activity is enhanced by known cAMP-elevating agents and by sulfhydryl compounds. The results of the present study are consistent with the hypothesis that the plasma-derived agent inhibits lympho-proliferation as a result of elevation of intracellular cAMP.     

Measurement of diameters of estuarine bacteria and particulates in natural water samples by use of a submicron particle analyzer

Desulfovibrio vulgaris strain Madison outcompetedMethanobacterium strain ivanov for hydrogen when sulfate was in excess because of higher cell yield and growth rate and a greater affinity for hydrogen as a consequence of a lower Km and higher Vmax for in vivo hydrogenase activity.Desulfovibrio vulgaris displayed a growth yield of 1.1 g/mol H₂, a Km for tritium exchange of 4 M, and a specific in vivo hydrogenase activity of 2.17 DPM³H₂O×10³/g cell protein/h; whereasMethanobacterium strain ivanov had a yield of 0.6 g/mol H₂, a Km for tritium exchange of 14 M, and a specific in vivo hydrogenase activity of 0.38 DPM³H₂O×10³/g cell protein/h. Under these physiological conditions, the Gibbs free-energy change associated with methanogenesis and sulfidogenesis from H₂ was calculated to be-47.4 kJ/mol and-62.9 kJ/mol, respectively. When sulfidogenesis was limited by sulfate concentration, the methanogen was able to successfully compete with the sulfidogen for hydrogen. Competition between methanogens and sulfidogens for hydrogen is explained in terms of thermodynamic, kinetic, and other important considerations not discussed in the previous literature.