Role of sodium on H+ excretion in the integument of the leopard frog Rana pipiens

1. The northern leopard frog, Rana pipiens, pipiens, in contrast to the southern leopard frog, Rana pipiens, berlandieri, did not demonstrate any significant H+ excretion across its integument even during a challenge of chronic metabolic acidosis. Likewise, no increase in the number of H+ secreting mitochondria-rich cells were observed in the northern frogs. 2. Under normal acid-base conditions in the southern frogs, H+ excretion was found to be dependent on mucosal sodium concentrations, whereas during chronic metabolic acidosis, H+ excretion was independent of mucosal sodium concentrations, but was amiloride sensitive. 3. High salinity adapted southern frogs, under normal and acidotic conditions, had enhanced H+ excretion rates as compared to the control non-salt adapted frogs. 4. Blood analyses demonstrated that significant acid-base changes were the result of systemic acidosis and not due to salt adaptations. Blood Na+ and K+ concentrations were also efficiently maintained during salt adaptations or chronic metabolic acidosis. 5. The results suggest that H+ excretion in epithelia can be influenced by the sodium transport state of the cell and the systemic acid-base profile. Models are proposed explaining these relationships.     

Properties of the oscillatory cAMP binding component of Dictyostelium discoideum cells and isolated plasma membranes.

The cAMP receptor on the surface of aggregation competent Dictyostelium discoideum cells specifically binds [3H]cAMP in an oscillatory manner with a periodicity of 2 min. The oscillatory cAMP-binding component is developmentallly regulated and has the nucleotide specificity expected for recognition of chemotactic signals. The concentration dependence of the peak amplitudes of cAMP binding exhibit an apparent threshold at 10(-8) M cAMP. The threshold concentration for cAMP binding that we measure is consistent with the concentration dependence of signal relay (cAMP secretion) and the chemotactic response. The kinetic data of binding and dissociation are very rapid, consistent with the time course of oscillations in receptor capacity (affinity). Specific binding oscillations are destroyed by heat or chymotrypsin but are insensitive to trypsin or glycosidase. A plasma membrane localization of receptor is supported by enrichment of cAMP binding in a plasma membrane preparation from differentiated cells. Receptor oscillations with a 2-min period are preserved in the membrane preparations, and the peak amplitudes are increased about 10-fold consistent with the enrichment of other plasma membrane markers. The alternating change in the receptor's binding capacity for cAMP may be the basis of the relay refractory period as well as the primary oscillator involved in the generation of postreceptor events such as stimulation of adenylate cyclase, cAMP secretion, and cellular movement, all of which have been previously shown to oscillate.     

Interaction of human thrombospondin with types I-V collagen: direct binding and electron microscopy

Binding of thrombospondin (TSP) to types I-V collagen was examined by direct binding assays using 125I-TSP and by visualization of rotary-shadowed intermolecular complexes in the electron microscope. The binding of TSP was highest to type V collagen in the absence of Ca, while lower but significant levels of binding were observed to all other collagen types in the presence or absence of Ca. Unlike intact TSP, the trimeric collagen-binding domain of TSP composed of 70-kD chains showed no Ca dependence in its binding to type V collagen. Further evidence for binding of TSP to types I and III collagen was obtained by competition studies in which these soluble collagens effectively inhibited binding of 125I-TSP to immobilized type V collagen. The binding of TSP to type V collagen was inhibited by heparin and fucoidin, both high-affinity ligands of TSP's heparin-binding domain. mAb A6.1, which binds to the 70-kD domain of TSP, is also the best of a panel of anti-TSP mAbs at inhibiting the TSP-collagen interaction. Electron microscopy of rotary-shadowed replicas of TSP-collagen complexes revealed that all five types of collagen examined had a binding site for TSP at one end of the pepsinized, triple helical molecule. The specificity of this site was tested by examining the ability of BSA to form a complex with the end of the pepsinized collagens. Rotary-shadowed replicas revealed a low frequency of apparent BSA-collagen complexes, and histograms of these data showed no evidence for the preferential association of BSA with the end of the collagen molecules. In addition to the specific end site, type V collagen had an internal binding site for TSP located about two-thirds of the distance along the length of the collagen molecule from the end site. The internal binding site for TSP on type V collagen is apparently the site responsible for the higher affinity binding of TSP to that protein observed in direct binding assays. The trimeric 70-kD collagen-binding domain of TSP bound to the same sites on the collagens as did intact TSP.     

The taxonomic status and distribution of Bushbabies in Malawi with emphasis on the significance of vocalizations

The debated identity of a small forest bushbaby in Malawi is resolved by a short-term field study of the animals’ behavior. Locomotor styles, calling patterns, and the structure of advertising calls confirm that the species is Galago zanzibaricusrather than G. demidoffor G. thomasi.A detailed comparison of acoustic structure between the Malawi animals and G. zanzibaricusin Kenya demonstrates a degree of between-population variation, although the calls remain conservative in those parameters expected to aid recognition of conspecifics. Distribution records extend the known geographical range of G. zanzibaricusover most of the northern half of Malawi. Further studies are required to link the animals from this region with either of the previously recognized subspecies: G. z. zanzibaricusfrom East Africa or G. z. grantifrom southern Malawi, Mozambique, and Zimbabwe.     

An analysis of an ordinary differential equation model for a two-species predator-prey system with harvesting and stocking

An analysis is presented for a model of a two-species predator-prey system where each species can be harvested or stocked. Using methods from bifurcation theory the qualitative nature of the steady-state solutions is examined. The effect of harvesting and stocking rates and the prey carrying capacity is examined in detail.     

Characteristics of dynamic postural reactions in the locust hindleg

Summary The use of the locust (Schistocerca americana) hindleg in postural control was examined in animals that stood on a repeatedly swayed vertical substrate. Myograms were recorded from leg muscles and the angle of the femoro-tibial joint was monitored photographically. Two discrete strategies were observed,; in compensatory reactions the hindleg was held in place, while in flexion reactions, the leg was moved, most often to complete flexion of the femoro-tibial joint. Tightly coupled, rhythmic bursting occurred in the flexor and levator muscles of the leg during compensatory reactions. Bursting was initiated repeatedly when the substrate was being pulled away from the animal. Bursting was correlated with subsequent decreases in the rate of change of the femorotibial joint angle. Compensatory and flexion reactions occurred preferentially in different ranges of joint angles: most often, compensatory reactions occurred in the midrange, while flexion reactions were elicited in the extremes of joint angle. These differences may be due to the mechanical advantages of the tibial muscles and the leg may be moved to full flexion because of a locking mechanism of the flexor muscle tendon. These reactions are compared with known reflexes of hindleg proprioceptors and contrasted with similar responses of vertebrates.     

The malmö polymorphism of coagulation factor IX, an immunologic polymorphism due to dimorphism of residue 148 that is in linkage disequilibrium with two other F.IX polymorphisms

A mouse monoclonal antibody (MAB 9.9) to coagulation factor IX (F.IX) detects a polymorphism in the plasma of normal people. Its epitope has been narrowed down to <6 amino acids in the activation peptide of the X-linked F.IX protein. The activation peptide contains a dimorphism—Thr:Ala—at position 148 of the protein. Using synthetic oligonucleotides, we have demonstrated that (1) the F.IX which reacts with 9.9 has Thr at position 148 and (2) that which does not has Ala. Positive reactors (148^thr) are designated Malmö A, and negative reactors (148^ala) are designated Malmö B. The plasma levels of AA women are indistinguishable from those of A men, and both B men and BB women are null against MAB 9.9. The plasma level of Malmö A in AB women is approximately half that of AA women, and “lyonization” is clearly operating in the heterozygotes. The dimorphism is in strong linkage disequilibrium with two other intragenic RFLPs, TaqI and XmnI. Furthermore, intragenic crossing-over—including double crossing-over—appears to have occurred between the three sites. Seven of the eight possible haplotypes have been identified, five in men and two others in women. The immunoassay that identifies ～50% of the AB women in the pool of Malmö A females with 95% confidence identifies men unambiguously as A or B. The assay would be very useful for population-genetic studies of the Malmö epitope if the studies were limited to men.