Probing the substrate-binding sites of aminoacyl-tRNA synthetases with the procion dye green HE-4BD.

In contrast with previous reports, it was found that membrane-protein phosphorylation by the catalytic subunit (CS) of cyclic AMP-dependent protein kinase had no effect on Ca2+ uptake into platelet membrane vesicles or on subsequent Ca2+ release by inositol 1,4,5-trisphosphate (IP3). Furthermore, IP-20, a highly potent synthetic peptide inhibitor of CS, which totally abolished membrane protein phosphorylation by endogenous or exogenous CS, also had no effect on either Ca2+ uptake or release by IP3. Commercial preparations of protein kinase inhibitor protein (PKI) usually had no effect, but one preparation partially inhibited Ca2+ uptake, which is attributable to the gross impurity of the commercial PKI preparation. IP3-induced release of Ca2+ was also unaffected by the absence of ATP from the medium, supporting the conclusion that Ca2+ release by IP3 does not require the phosphorylation of membrane protein.     

Haematological and rheological characteristics of blood in seven marine mammal species: physiological implications for diving behaviour

The haeniatological and rheological characteristics of blood from seven marine mammal species have been examined to determine the relationship between increased haematocrit. which is correlated with the ability to increase aerobic dive limits. and blood viscosity. The species examined reflect adaptations to a variety of marine niches ranging from coastal to pelagic to iceedge environments. and exhibit a wide range of diving behaviours. Average haematocrits ranged from43–45% in bottlenose dolphins. killer whales and California sea lions to more than 60% in the deeper diving species (beluga whales and northern elephant seals). Whole blood viscosity () increased exponentially with haematocrit (= 0.96*e^0-0335*Hct). representin a two-fold increase from 4.1 cP for killer whale blood to 8.9 cP for northern elephant seal. There was no apparent compensatory mechanism to reduce viscosity at any shear rate. The optimal haematocrit for oxygen transport was calculated to be40–50% for all species tested. The species with lower haematocrits were within optimal values for oxygen transport. while the two species with the highest haematocrits (beluga whales and northern elephant seals) were above predicted optimal oxygen transport values. On the basis of comparisons of the diving behaviour of these seven species, we suggest that marine mammal species with the greatest adaptation for increased oxygen stores via increased haematocrit have the capacity for deep, long-duration dives, but a limited oxygen transport capacity. We predict that this compromise precludes fast sustainable swimming behaviour in these species.     

Resident mesenchymal cells and fibrosis

Fibrosis is a major clinical problem associated with as many as 45% of all natural deaths in developed nations.It can affect all organs and accumulating evidence indicates that fibrogenesis is not merely a bystander product of injury, but is a central pathological problem directly contributing to loss of organ function. In the majority of clinical cases, fibrogenesis is strongly associated with the recruitment of leukocytes, even in the absence of infection. Although chronic infections are a significant cause of fibrogenesis, in most cases fibrotic disease occurs in the context of sterile injury, such as microvascular disease, toxic epithelial injury or diabetes mellitus. Fibrogenesis is a direct consequence of the activation of extensive, and previously poorly appreciated, populations of mesenchymal cells in our organs which are either wrapped around capillaries and known as ‘pericytes’, or embedded in interstitial spaces between cell structures and known as resident ‘fibroblasts’. Recent fate-mapping and complementary studies in several organs indicate that these cells are the precursors of the scar-forming myofibroblasts that appear in our organs in response to injury. Here we will review the literature supporting a central role for these cells in fibrogenesis, and highlight some of the critical cell to cell interactions that are necessary for the initiation and continuation of the fibrogenic process. This article is part of a Special Issue entitled: Fibrosis: Translation of basic research to human disease.     

Spatial patterns of extra‐pair paternity for spotted towhees Pipilo maculatus in urban parks

The extra‐pair (EP) mating system of birds may be influenced by food resources, such that nutritionally stressed females are unable to pursue EP fertilizations (constrained female hypothesis; CFH), or that females on poor territories acquire EP fertilizations during extra‐territorial forays in search of food (mating opportunity hypothesis; MOH). Edges of urban habitat fragments are sites of apparent high food abundance for spotted towhees Pipilo maculatus, and we used distance to habitat edge in four urban parks in Portland, OR, USA (2004–2006), to test the CFH and MOH. EP paternity was independent of park identity and year; 44% of nests contained EP young and 26% of all young were EP. As predicted by the CFH, EP paternity was more common in nests of long‐tailed (presumably) high quality females. However, independently of tail length, younger females had more EP young than older females, a finding consistent with the MOH. Contrary to predictions of both hypotheses, the probability that a nest contained EP young was highest both at the habitat edge and habitat interior while the proportion of young in nests of EP origin (for nests with EP young) was highest at intermediate distances from habitat edge. We propose that high frequency of EP paternity among females in the interior occurred because, as predicted by the MOH, they ranged more widely in search of food and often encountered EP males. High probability of EP paternity near edges was likely unrelated to female quality. Instead, anthropogenic food sources may have attracted individuals to edges and increased encounters between potential EP mates. Simple opportunity seems likely to account for patterns of EP paternity in spotted towhees, suggesting that human altered environments have the potential to substantially affect EP mating behavior.