Characterization of cross-bridge elasticity and kinetics of cross-bridge cycling during force development in single smooth muscle cells

Force development in smooth muscle, as in skeletal muscle, is believed to reflect recruitment of force-generating myosin cross-bridges. However, little is known about the events underlying cross-bridge recruitment as the muscle cell approaches peak isometric force and then enters a period of tension maintenance. In the present studies on single smooth muscle cells isolated from the toad (Bufo marinus) stomach muscularis, active muscle stiffness, calculated from the force response to small sinusoidal length changes (0.5% cell length, 250 Hz), was utilized to estimate the relative number of attached cross-bridges. By comparing stiffness during initial force development to stiffness during force redevelopment immediately after a quick release imposed at peak force, we propose that the instantaneous active stiffness of the cell reflects both a linearly elastic cross-bridge element having 1.5 times the compliance of the cross-bridge in frog skeletal muscle and a series elastic component having an exponential length-force relationship. At the onset of force development, the ratio of stiffness to force was 2.5 times greater than at peak isometric force. These data suggest that, upon activation, cross-bridges attach in at least two states (i.e., low-force-producing and high-force-producing) and redistribute to a steady state distribution at peak isometric force. The possibility that the cross-bridge cycling rate was modulated with time was also investigated by analyzing the time course of tension recovery to small, rapid step length changes (0.5% cell length in 2.5 ms) imposed during initial force development, at peak force, and after 15 s of tension maintenance. The rate of tension recovery slowed continuously throughout force development following activation and slowed further as force was maintained. Our results suggest that the kinetics of force production in smooth muscle may involve a redistribution of cross-bridge populations between two attached states and that the average cycling rate of these cross-bridges becomes slower with time during contraction.     

Does biology underlie the oldest profession? Prostitution and sex disparities in john behavior

This study considers a biosocial explanation of why johns, the purchasers of commercial sex exchanges, are almost exclusively male. Trivers's theory of parental investment and sexual selection predicts that differential parental investment by biological sex will lead to divergent sex-based reproductive instincts. The sex bearing the larger parental investment will tend to be choosier whereas the sex bearing the lesser investment will tend to be relatively indiscriminate and competitive for access to sexual resources. We hypothesized that men are more likely than women to offer objects of value in exchange for access to sexual resources. Using self-reports of sex-purchasing from Add Health data (N = 14,544), we found that maleness was a robust predictor of john behavior even after controlling for well-known criminogenic risk factors.     

Thapsigargin induces mitochondrial dysfunction and apoptosis in the mastocytoma P815 cell line and in mouse thymocytes

Thapsigargin is a plant-derived inhibitor of the endoplasmic reticulum Ca(2+)-ATPase.Treatment with thapsigargin leads to a rapid, large and prolonged increase in the intracellular calcium ion concentration ([Ca(2+)](i)). Previously thapsigargin has been shown to inhibit proliferation and induce apoptosis. Here we report the results of thapsigargin treatment in thymocytes harvested from 10-day-old mice and in the P815 mastocytoma cell line. In thapsigargin-treated cells we observed enlarged mitochondria with disrupted cristae structure. These mitochondria closely resembled those observed after the induction of phase transition. To determine if the mitochondria were functioning normally the cells were stained with rhodamine 123 (R123) and analysed with flow cytometry. After thapsigargin treatment the R123 staining decreased, indicative of a loss of mitochondrial membrane potential. Furthermore intracellular ATP concentrations were also found to be reduced in cells treated with thapsigargin. Taken together these results indicate an increase in the [Ca(2+)](i) caused by thapsigargin treatment results in dysfunctional mitochondria and reduced ATP. We propose that this decrease in the concentration of ATP provokes the onset of thapsigargin-induced apoptosis. To investigate the effect of thapsigargin treatment on the cell cycle, rapidly cycling P815 cells were sorted into populations enriched for either G(0)/G(1) or S/G(2)/M phases, and these populations were then treated with thapsigargin. Thapsigargin treatment induced a cell cycle block before S phase. We propose that the block in the cell cycle induced by thapsigargin was a result of the decreased intracellular ATP concentration interfering with the energy requiring processes of DNA replication. The block could also be related to the high intracellular calcium ion concentration that would interfere with the subtle calcium transients involved in the cell's preparations for replication and mitosis. Apoptosis occurred to an equal extent in both populations of cells.     

Chaetomium elatum (Kunze: Chaetomiaceae) as a root-colonizing fungus in avocado: is it a mutualist, cheater, commensalistic associate, or pathogen?

Plants support numerous root colonists that may share morphological characteristics with mycorrhizal fungi but may play different roles in the rhizosphere. To determine the function of one such root-colonizing fungus, Chaetomium elatum, the infectivity and composition of inoculum containing C. elatum were varied independently of and in association with the known mutualist Glomus intraradices under two light intensities. Maximum plant benefit occurred with mixtures of both G. intraradices and C. elatum and under high light intensity. Under low light intensity and in monoculture, C. elatum functioned as a weak pathogen that was able to kill host plants. Here, maximum plant mortality was associated with the highest levels of C. elatum infectivity. When G. intraradices was present, no negative impact of C. elatum was detected. Intraspecific interactions were important in predicting sporulation rates for both fungi, whereas no interspecific fungal interactions were detected. In the presence of G. intraradices, C. elatum appears to function as a "commensalistic associate," neither impacting plant growth nor sporulation by G. intraradices. Overall, C. elatum appears to be multifunctional, serving as both a rhizoplane and rhizophere fungus, opportunistically colonizing plant roots and only becoming pathogenic when resources are severely limited and intraspecific competition is high. This multifunctional strategy may be shared with other fungi that form similar structures in roots.     

Der Einfluss verschiedener Fixierungsmittel auf das Strukturbild der Präputialdrüsen der Ratte

Summary The influence of various methods of fixation on the preputial gland of the rat was investigated. In addition to the lipids, the cells contain numerous granules which are dissolved by alcoholic and certain acid fixatives. In future investigation concerning either the histochemistry of the gland or the effect on the gland of various experimental conditions, its peculiar ability to secrete two different substances must be considered. In any event the preputial gland of the rat is more than a simple sebaceous gland.     

Alteration by hyperoxia of ventilatory dynamics during sinusoidal work

The effects of hyperoxia on ventilatory and gas exchange dynamics were studied utilizing sinusoidal work rate forcings. Five subjects exercised on 14 occasions on a cycle ergometer for 30 min with a sinusoidally varying work load. Tests were performed at seven frequencies of work load during air or 100% O2 inspiration. From the breath-by-breath responses to these tests, dynamic characteristics were analyzed by extracting the mean level, amplitude of oscillation, and phase lag for each six variables with digital computer techniques. Calculation of the time constant (tau) of the ventilatory responses demonstrated that ventilatory kinetics were slower during hyperoxia than during normoxia (P less than 0.025; avg 1.56 and 1.13 min, respectively). Further, for identical work rate fluctuations, end-tidal CO2 tension fluctuations were increased by hyperpoxia. Ventilation during hyperoxia is slower to respond to variations in the level of metabolically produced CO2, presumably because hyperoxia attenuates carotid body output; the arterial CO2 tension is consequently less tightly regulated.     

Evolution of the 28S ribosomal RNA gene in anurans: regions of variability and their phylogenetic implications

Fifteen restriction sites were mapped to the 28S ribosomal RNA gene of individuals representing 54 species of frogs, two species of salamanders, a caecilian, and a lungfish. Eight of these sites were present in all species examined, and two were found in all but one species. Alignment of these conserved restriction sites revealed, among anuran 28S rRNA genes, five regions of major length variation that correspond to four of 12 previously identified divergent domains of this gene. One of the divergent domains (DD8) consists of two regions of length variation separated by a short segment that is conserved at least throughout tetrapods. Most of the insertions, deletions, and restriction-site variations identified in the 28S gene will require sequence-level analysis for a detailed reconstruction of their history. However, an insertion in DD9 that is coextensive with frogs in the suborder Neobatrachia, a BstEII site that is limited to representatives of two leptodactylid subfamilies, and a deletion in DD10 that is found only in three ranoid genera are probably synapomorphies.      

The gut hormones PYY 3-36 and GLP-1 7-36 amide reduce food intake and modulate brain activity in appetite centers in humans

Obesity is a major public health issue worldwide. Understanding how the brain controls appetite offers promising inroads toward new therapies for obesity. Peptide YY (PYY) and glucagon-like peptide 1 (GLP-1) are coreleased postprandially and reduce appetite and inhibit food intake when administered to humans. However, the effects of GLP-1 and the ways in which PYY and GLP-1 act together to modulate brain activity in humans are unknown. Here, we have used functional MRI to determine these effects in healthy, normal-weight human subjects and compared them to those seen physiologically following a meal. We provide a demonstration that the combined administration of PYY(3-36) and GLP-1(7-36 amide) to fasted human subjects leads to similar reductions in subsequent energy intake and brain activity, as observed physiologically following feeding.