Frequency-dependent acceleration of relaxation involves decreased myofilament calcium sensitivity

The force-frequency relationship is an intrinsic modulator of cardiac contractility and relaxation. Force of contraction increases with frequency, while simultaneously a frequency-dependent acceleration of relaxation occurs. While frequency dependency of calcium handling and sarcoplasmic reticulum calcium load have been well described, it remains unknown whether frequency-dependent changes in myofilament calcium sensitivity occur. We hypothesized that an increase in heart rate that results in acceleration of relaxation is accompanied by a proportional decrease in myofilament calcium sensitivity. To test our hypothesis, ultrathin right ventricular trabeculae were isolated from New Zealand White rabbit hearts and iontophorically loaded with the calcium indicator bis-fura 2. Twitch and intracellular calcium handling parameters were measured and showed a robust increase in twitch force, acceleration of relaxation, and rise in both diastolic and systolic intracellular calcium concentration with increased frequency. Steady-state force-intracellular calcium concentration relationships were measured at frequencies 1, 2, 3, and 4 Hz at 37 degrees C using potassium-induced contractures. EC(50) significantly and gradually increased with frequency, from 475 +/- 64 nM at 1 Hz to 1,004 +/- 142 nM at 4 Hz (P < 0.05) and correlated with the corresponding changes in half relaxation time. No significant changes in maximal active force development or in the myofilament cooperativity coefficient were found. Myofilament protein phosphorylation was assessed using Pro-Q Diamond staining on protein gels of trabeculae frozen at either 1 or 4 Hz, revealing troponin I and myosin light chain-2 phosphorylation associated with the myofilament desensitization. We conclude that myofilament calcium sensitivity is substantially and significantly decreased at higher frequencies, playing a prominent role in frequency-dependent acceleration of relaxation.     

Multiple hypotheses explain variation in extra‐pair paternity at different levels in a single bird family

Extra‐pair paternity (EPP), where offspring are sired by a male other than the social male, varies enormously both within and among species. Trying to explain this variation has proved difficult because the majority of the interspecific variation is phylogenetically based. Ideally, variation in EPP should be investigated in closely related species, but clades with sufficient variation are rare. We present a comprehensive multifactorial test to explain variation in EPP among individuals in 20 populations of nine species over 89 years from a single bird family (Maluridae). Females had higher EPP in the presence of more helpers, more neighbours or if paired incestuously. Furthermore, higher EPP occurred in years with many incestuous pairs, populations with many helpers and species with high male density or in which males provide less care. Altogether, these variables accounted for 48% of the total and 89% of the interspecific and interpopulation variation in EPP. These findings indicate why consistent patterns in EPP have been so challenging to detect and suggest that a single predictor is unlikely to account for the enormous variation in EPP across levels of analysis. Nevertheless, it also shows that existing hypotheses can explain the variation in EPP well and that the density of males in particular is a good predictor to explain variation in EPP among species when a large part of the confounding effect of phylogeny is excluded.     

The relative importance of male tail length and nuptial plumage on social dominance and mate choice in the red-backed fairy-wren Malurus melanocephalus: evidence for the multiple receiver hypothesis

Understanding why males of many species exhibit two or more sexual ornaments depends upon identifying both the information conveyed and the intended receiver(s) for each signal. Here we focus on identifying the intended receivers for two sexual signals exhibited by male red-backed fairy-wrens Malurus melanocephalus , extent of nuptial plumage and tail length. In doing so we test the multiple receiver hypothesis, which predicts that each trait is directed toward a different type of receiver (e.g., males vs females). Male red-backed fairy-wrens in nuptial plumage exhibit reversed sexual dimorphism for tail length in the breeding season, when their tails are significantly shorter than those of females or males in eclipse plumage. Using both aviary-based experiments and indices of mate choice and social dominance from a natural population, we found that extent of nuptial plumage and age primarily affected female mate choice and that shorter tails were primarily associated with male:male dominance signaling. The field and aviary studies combined are consistent with the multiple receiver hypothesis, in that each trait appears to be directed primarily to a different set of receivers (plumage for females and tail length for males), though each trait may also signal information to the other set of receivers as well. We propose that sexual selection may favor shorter tail lengths in male red-backed fairy-wrens through social competition mechanisms.     

A Comparison of the Use of In Vitro-Transcribed and Native rRNA for the Quantification of Microorganisms in the Environment

Abstract Nearly full-length, small subunit (SSU) rRNA was transcribed in vitro from clones of SSU rDNA genes. Comparing the use of in vitro-transcribed and native rRNA indicated that, when in vitro-transcribed rRNA was used as a standard for quantitative hybridizations with oligonucleotide probes, the population was consistently underestimated. The population abundance was expressed as a percentage of specific target SSU rRNA (determined with a specific oligonucleotide probe), relative to the total SSU rRNA (measured with a universal probe). Differences in hybridization signals could be related to specific probe target locations and rRNA denaturation conditions, suggesting that higher order structure is important in quantitative membrane hybridizations. Therefore, in vitro-transcribed rRNA cannot always be used for the absolute quantification of microbial populations, but can be employed as a standard to quantify shifts in population abundance over time, and to compare community structure in various environments.     

Gender comparison of contractile performance and beta-adrenergic response in isolated rat cardiac trabeculae

It is known that gender can affect susceptibility to development of various cardiomyopathies. However, it is unclear whether basic mechanical contractile function of the myocardium differs between genders, whether they respond differently to stressors, or both. To test for a possible gender factor, contractile parameters of healthy, isolated myocardium were investigated under near physiological conditions. Right ventricular ultra-thin trabeculae from young adult LBN-f1 rats were electrically stimulated to isometrically contract at 37°C. No differences were found in developed force or kinetic parameters. In each muscle, the force-frequency relationship was measured at 4, 6, and 8 Hz, encompassing most of the in vivo range. Again, no differences were observed in force-frequency behavior; developed force rose from 21.6 ± 4.0 at 4 Hz to 30.3 ± 5.8 mN/mm² at 8 Hz in females and from 23.4 ± 3.4 to 29.8 ± 3.4 mN/mm² in males. The response to β-adrenergic stimulation was similar; at 1 μM isoproterenol, developed force increased to 34.5 ± 6.2 mN/mm² in females and 32.3 ± 3.2 mN/mm² in males (female vs. male, not significant). We conclude that basic mechanical performance of healthy isolated myocardium under physiological conditions is not different between males and females, and a different response to stress must underlie gender-based differences in cardiac performance.     

Mutations in the gene encoding the Sigma 2 subunit of the adaptor protein 1 complex, AP1S2, cause X-linked mental retardation

In a systematic sequencing screen of the coding exons of the X chromosome in 250 families with X-linked mental retardation (XLMR), we identified two nonsense mutations and one consensus splice-site mutation in the AP1S2 gene on Xp22 in three families. Affected individuals in these families showed mild-to-profound mental retardation. Other features included hypotonia early in life and delay in walking. AP1S2 encodes an adaptin protein that constitutes part of the adaptor protein complex found at the cytoplasmic face of coated vesicles located at the Golgi complex. The complex mediates the recruitment of clathrin to the vesicle membrane. Aberrant endocytic processing through disruption of adaptor protein complexes is likely to result from the AP1S2 mutations identified in the three XLMR-affected families, and such defects may plausibly cause abnormal synaptic development and function. AP1S2 is the first reported XLMR gene that encodes a protein directly involved in the assembly of endocytic vesicles.     

Microbial Reprogramming Inhibits Western Diet-Associated Obesity

A recent epidemiological study showed that eating ‘fast food’ items such as potato chips increased likelihood of obesity, whereas eating yogurt prevented age-associated weight gain in humans. It was demonstrated previously in animal models of obesity that the immune system plays a critical role in this process. Here we examined human subjects and mouse models consuming Westernized ‘fast food’ diet, and found CD4⁺ T helper (Th)17-biased immunity and changes in microbial communities and abdominal fat with obesity after eating the Western chow. In striking contrast, eating probiotic yogurt together with Western chow inhibited age-associated weight gain. We went on to test whether a bacteria found in yogurt may serve to lessen fat pathology by using purified Lactobacillus reuteri ATCC 6475 in drinking water. Surprisingly, we discovered that oral L. reuteri therapy alone was sufficient to change the pro-inflammatory immune cell profile and prevent abdominal fat pathology and age-associated weight gain in mice regardless of their baseline diet. These beneficial microbe effects were transferable into naïve recipient animals by purified CD4⁺ T cells alone. Specifically, bacterial effects depended upon active immune tolerance by induction of Foxp3⁺ regulatory T cells (Treg) and interleukin (Il)-10, without significantly changing the gut microbial ecology or reducing ad libitum caloric intake. Our finding that microbial targeting restored CD4⁺ T cell balance and yielded significantly leaner animals regardless of their dietary ‘fast food’ indiscretions suggests population-based approaches for weight management and enhancing public health in industrialized societies.     

Mutations in ZDHHC9, which encodes a palmitoyltransferase of NRAS and HRAS, cause X-linked mental retardation associated with a Marfanoid habitus

We have identified one frameshift mutation, one splice-site mutation, and two missense mutations in highly conserved residues in ZDHHC9 at Xq26.1 in 4 of 250 families with X-linked mental retardation (XLMR). In three of the families, the mental retardation phenotype is associated with a Marfanoid habitus, although none of the affected individuals meets the Ghent criteria for Marfan syndrome. ZDHHC9 is a palmitoyltransferase that catalyzes the posttranslational modification of NRAS and HRAS. The degree of palmitoylation determines the temporal and spatial location of these proteins in the plasma membrane and Golgi complex. The finding of mutations in ZDHHC9 suggests that alterations in the concentrations and cellular distribution of target proteins are sufficient to cause disease. This is the first XLMR gene to be reported that encodes a posttranslational modification enzyme, palmitoyltransferase. Furthermore, now that the first palmitoyltransferase that causes mental retardation has been identified, defects in other palmitoylation transferases become good candidates for causing other mental retardation syndromes.