Mechanical stretch promotes alveolar epithelial type II cell differentiation.

Functional maturation of pulmonary alveolar epithelial cells is crucial for extrauterine survival. Mechanical distension and mesenchymal-epithelial interactions play important roles in this process. We hypothesized that mechanical stretch simulating fetal breathing movements is an important regulator of pulmonary epithelial cell differentiation. Using a Flexercell Strain Unit, we analyzed effects of stretch on primary cultures of type II cells and cocultures of epithelial and mesenchymal cells isolated from fetal rat lungs during late development. Cyclic stretch of isolated type II cells increased surfactant protein (SP) C mRNA expression by 150 +/- 30% over controls (P < 0.02) on gestational day 18 and by 130 +/- 30% on day 19 (P < 0.03). Stretch of cocultures with fibroblasts increased SP-C expression on days 18 and 19 by 170 +/- 40 and 270 +/- 40%, respectively, compared with unstretched cocultures. On day 19, stretch of isolated type II cells increased SP-B mRNA expression by 50% (P < 0.003). Unlike SP-C, addition of fibroblasts did not produce significant additional effects on SP-B mRNA levels. Under these conditions, we observed only modest increases in cellular immunoreactive SP-B, but secreted saturated phosphatidylcholine rose by 40% (P < 0.002). These results indicate that cyclic stretch promotes developmentally timed differentiation of fetal type II cells, as a direct effect on epithelial cell function and via mesenchymal-epithelial interactions. Expression of the SP-C gene appears to be highly responsive to mechanical stimulation.     

Effect of deuteration and cryosolvents on the energy transduction in primary processes of photosynthesis.

Effects of cryosolvents and D2O/H2O substitution on the reaction centres (RCs) isolated from photosynthetic bacteria were studied with respect to the role of intra-protein hydrogen bonds in the primary photosynthetic electron transfer. As a result of such treatment of RCs, the charge separation rate between the photoactive bacteriochlorophyll (P2 dimer) and bacteriopheophytin and the rate of electron transfer to the primary quinone slowed down. The energy migration rate from bacteriopheophytin (BPheM), inactive in electron transport, to P2 decreased as well. Although cryosolvents can shift the redox potential of the photoactive pigment, there is no direct correlation between the P2 potential and the effects of these modifying agents on the photosynthetic process in RCs occurring with participation of P2. The removal of H subunit from the pigment-protein complex results in the pronounced weakening of the dimethyl sulfoxide modifying effects on the RC hydrogen bonds. The role of structural and dynamic state in the functioning of the photosynthetic bacterial RCs is analyzed. Relaxation processes in purple bacteria RCs accompanying the primary picosecond steps of energy transformation proceed with the participation of small proton-containing molecular groups in the immediate surroundings of electron transfer carriers. In this paper, we present results concerning mechanisms of primary photosynthetic steps, which were initiated by A. A. Krasnovsky and have been studied for several years at the Department of Biophysics. This paper is dedicated to the memory of our teacher Prof. A. A. Krasnovsky.     

Induction of pseudofoci and inhibition of density-mediated neoplastic transformation by PMA in NIH 3T3 cells after short-term exposures

Summary Depending on the precise conditions and cellular starting material, phorbol-13-myristate-12-acetate (PMA) can induce or suppress the transformation of NIH 3T3 cells. In sublines that do not undergo rapid transformation, exposure to PMA over the course of several weeks accelerated the process, while sublines that are primed for density-mediated transformation respond to PMA with a suppression of the process. This study examines the latter phenomenon. Within 1 h of exposure to 0.02μg/ml PMA, sparse cultures had undergone a morphological transition after which the cells appeared smaller and the processes thinner. These sublines exhibited a two-to sixfold increase in the saturation density achieved in 2% calf serum (CS). Phorbol ester analogs with hydrocarbon substitutions of 4 or more carbons at positions 12 and 13 of the phorbol nucleus had a similar effect as PMA on the saturation density. High concentrations of PMA (1μg/ml) induced the formation of cell aggregates (pseudofoci) that resembled transformed foci in their high local density, but unlike transformed foci, did not reinitiate focus formation if the cells were diluted and replated without PMA as secondary cultures. PMA inhibited the processes of neoplastic transformation and progression that occur readily in these NIH 3T3 sublines when they reach high cell density. I suggest that such changes occur because PMA abolishes the selection pressure at high densities that favors the transformation of some cells in heterogeneous populations. Induction of transformation by PMA (reported previously) occurs after much longer exposures in sublines that are relatively resistant to rapid density-mediated transformation. These results are discussed in the context of progressive state selection, a concept that has been developed to account for spontaneous transformation in this system.     

Fetal Loss After Cholecystectomy During Pregnancy

The histories of 17 patients who had a cholecystectomy during pregnancy were reviewed. All patients were operated upon for clinical recurrent biliary colic. Four patients aborted or had premature labour. It appears that there is an increased risk of fetal loss if cholecystectomy is performed during pregnancy. Because of this, it would appear reasonable to perform the operation only if the exigencies of the situation demand that surgery be done. It should be borne in mind that there may also be an increased fetal loss from recurrent biliary colic treated symptomatically, particularly if cholecystitis and jaundice were to complicate matters further. If operation is performed, the fetal loss rate will likely be in the neighbourhood of 15%.     

Multiple timescale mixed bursting dynamics in a respiratory neuron model

Experimental results in rodent medullary slices containing the pre-Bötzinger complex (pre-BötC) have identified multiple bursting mechanisms based on persistent sodium current (I _NaP) and intracellular Ca²⁺. The classic two-timescale approach to the analysis of pre-BötC bursting treats the inactivation of I _NaP, the calcium concentration, as well as the Ca²⁺-dependent inactivation of IP ₃ as slow variables and considers other evolving quantities as fast variables. Based on its time course, however, it appears that a novel mixed bursting (MB) solution, observed both in recordings and in model pre-BötC neurons, involves at least three timescales. In this work, we consider a single-compartment model of a pre-BötC inspiratory neuron that can exhibit both I _NaP and Ca²⁺ oscillations and has the ability to produce MB solutions. We use methods of dynamical systems theory, such as phase plane analysis, fast-slow decomposition, and bifurcation analysis, to better understand the mechanisms underlying the MB solution pattern. Rather surprisingly, we discover that a third timescale is not actually required to generate mixed bursting solutions. Through our analysis of timescales, we also elucidate how the pre-BötC neuron model can be tuned to improve the robustness of the MB solution.     

Mucus-depleted frog palate as a model for the study of mucociliary clearance

To better understand the frog palate model of mucociliary transport, we measured the transport rate of mucus (MTR) from the leopard frog, Rana pipiens, and from the bullfrog, R. catesbeiana, recorded the stability of the MTR over a period of hours and days and over the course of 1 yr, and measured the viscoelasticity, percent solid composition, and spinnability (filance) of mucus from both species. Bullfrog mucus was less rigid than leopard frog mucus (log G* at 1 rad/s 2.09 vs. 2.61; P less than 0.01) and had a higher viscosity-to-elasticity ratio (tan delta at 1 rad/s 0.36 vs. 0.26; P less than 0.05). It also had a lower solids content (8.71 vs. 13.72%; P = 0.02), and there was a trend to lower spinnability for bullfrog mucus (filance 26.7 vs. 33.5 mm). These data suggest that bullfrog mucus has viscoelastic properties similar to normal mammalian respiratory mucus and leopard frog mucus has viscoelasticity similar to sputum samples. MTR was significantly slower in the winter than in the summer months (17 vs. 30 mm/min; P less than 0.0001). Although the leopard frog palate could be used for at least 7 consecutive days without exhaustion, bullfrog palates could be used for only 5 days. Palates of either species could generally be tested for 6 h/day without a significant decrease in MTR. These data clarify some of the sources of variability in the use of this system and suggest methods of standardization.     

The Cloning of the Bar Region and the B Breakpoint in Drosophila Melanogaster: Evidence for a Transposon-Induced Rearrangement

We have cloned the B breakpoint in Drosophila melanogaster using DNA from a P-M-induced revertant of B, which has a P element inserted at the B breakpoint. The analysis of the B DNA reveals that there is a transposable element, B104, right at the breakpoint. This suggests that this element may have been involved in the generation of the B breakpoint and the associated tandem duplication. One possible mechanism to generate the B duplication is a recombination event between two B104 elements, one at 16A1 and the other at 16A7. DNA sequencing data of the junctions of the B104 element support this model. Four partial revertants of B are the result of insertions of transposable elements very close to the B breakpoint. This supports the hypothesis that the breakpoint is the cause of the B mutation. The clones from B were used to isolate wild-type clones from 16A1, the location of the Bar gene. Four rearrangement breakpoints associated with various Bar mutations map within a 37-kb region, suggesting that the Bar gene is very large.