Quantal transmission at purinergic junctions: stochastic interaction between ATP and its receptors.

The time course of most quantal currents recorded with a small diameter electrode placed over visualized varicosities of sympathetic nerve terminals that secrete ATP was determined: these had a time to reach 90% of peak of 1.3-1.8 ms and a time constant of decay of 12-18 ms; they were unaffected by blocking ectoenzymes or the uptake of adenosine. Monte Carlo methods were used to analyze the stochastic interaction between ATP, released in a packet from a varicosity, and the underlying patch of purinoceptors, to reconstitute the time course of the quantal current. This leads to certain restrictions on the possible number of ATP molecules in a quantum (about 1000) and the density of purinoceptors at the junctions (about 1000 microns-1), given the known geometry of the junction and the kinetics of ATP action. The observed quantal current has a relatively small variability (coefficient of variation < 0.1), and this stochastic property is reproduced for a given quantum of ATP. Potentiation effects (of about 12%) occur if two quanta are released from the same varicosity because the receptor patch is not saturated even by the release of two quanta. The simulations show that quantal currents have a characteristically distinct shape for varicosities with different junctional cleft widths (50-200 nm). Finally, incorporation of an ectoenzyme with the known kinetics of ATPase into the junctional cleft allows for a quantal current of the observed time course, provided the number of ATP molecules in a quantum is increased over the number in the absence of the ATPase.     

Thermal biology of the common garter snake Thamnophis sirtalis (L.)

Summary The thermoregulatory significance of a striped-melanic colour polymorphism in the common garter snake, Thamnophis sirtalis, was assessed through a combination of labortory experimentation and field study. In experiments with living snakes the melanic morph maintained a higher body temperature than the striped morph, when exposed to natural insolation. Experiments with excised skin showed that this thermal advantage is attributable to some integumental difference between the two morphs. Body temperatures of snakes in the field revealed that, during the colder part of the active season, melanics were able to stay warmer than striped snakes by an amount (1.24 C°) approximating the difference observed in the laboratory. Some evidence and argument is presented to suggest that melanism also may confer protection against overheating in warm periods.     

Lecithostaphylus retroflexus (Molin, 1859) (Zoogonidae) and Tergestia acanthocephala (Stossich, 1887) (Fellodistomidae) (Digenea) from the epipelagic teleost Belone belone (L.) in the western Mediterranean

Numerous individuals of the poorly known species Lecithostaphylus retroflexus (Zoogonidae) and Tergestia acanthocephala (Fellodistomidae) have been recovered from the teleost fish Belone belone gracilis from off the Scandola Nature Reserve, Western Mediterranean. They are redescribed, incorporating previously undescribed features: for L. retroflexus, a post-oral ring, a bipartite seminal vesicle, the shape of the excretory vesicle, the subterminal excretory pore and the flask-shaped gland-cells associated with the distinctly pedunculate ventral sucker; and for T. acanthocephala, the intestinal bifurcation in the forebody, necessitating its return to the genus Tergestia from Theledera. Additionally, T. acanthocephala is compared with T. laticollis from various species of Trachurus from the same geographical area.     

New insights into the molecular and cellular functions of poly(ADP-ribose) and PARPs

Poly(ADP-ribose) polymerases (PARPs) are enzymes that transfer ADP-ribose groups to target proteins and thereby affect various nuclear and cytoplasmic processes. The activity of PARP family members, such as PARP1 and PARP2, is tied to cellular signalling pathways, and through poly(ADP-ribosyl)ation (PARylation) they ultimately promote changes in gene expression, RNA and protein abundance, and the location and activity of proteins that mediate signalling responses. PARPs act in a complex response network that is driven by the cellular, molecular and chemical biology of poly(ADP-ribose) (PAR). This PAR-dependent response network is crucial for a broad array of physiological and pathological responses and thus is a good target for chemical therapeutics for several diseases.     

The partial characterization of alcohol dehydrogenase null alleles from natural populations ofDrosophila melanogaster

Twenty-three alcohol dehydrogenase (ADH) putative null alleles extracted from four Tasmanian (Australia) populations of Drosophila melanogaster produce no ADH activity and are unable to form active heterodimers with either AdhF or AdhS. Twelve of these nulls were tested by enzyme-linked immunosorbent assay (ELISA) and did not produce any ADH cross-reacting material (CRM). The null homozygotes had similar, but slightly lower, mortalities on ethanol-supplemented media compared to an artificially induced null allele. Heterozygotes between the null alleles and standard AdhF and AdhS alleles had intermediate ADH activity and CRM levels.     

Optimum activity of the phosphofructokinase from Ascaris suum requires more than one metal ion

Phosphofructokinase (PFK) catalyzes the phosphorylation of fructose 6-phosphate (F6P) to give fructose 1,6-bisphosphate (FBP) using MgATP as the phosphoryl donor. As the concentration of Mg(2+) increases above the concentration needed to generate the MgATP chelate complex, a 15-fold increase in the initial rate was observed at low MgATP. The effect of Mg(2+) is limited to V/K(MgATP), and initial rate studies indicate an equilibrium-ordered addition of Mg(2+) before MgATP. Isotope partitioning of the dPFK:MgATP complex indicates a random addition of MgATP and F6P at low Mg(2+), with the rate of release of MgATP from the central E:MgATP:F6P complex 4-fold faster than the net rate constant for catalysis. This can be contrasted with the ordered addition of MgATP prior to F6P at high Mg(2+). The addition of fructose 2,6-bisphosphate (F26P(2)) has no effect on the mechanism at low Mg(2+), with the exception of a 4-fold increase in the affinity of the enzyme for F6P. At high Mg(2+), F26P(2) causes the kinetic mechanism to become random with respect to MgATP and F6P and with MgATP released from the central complex half as fast as the net rate constant for catalysis. The latter is in agreement with previous studies [Gibson, G. E., Harris, B. G., and Cook, P. F. (1996) Biochemistry 35, 5451-5457]. The overall effect of Mg(2+) is a decrease in the rate of release of MgATP from the E:MgATP:F6P complex, independent of the concentration of F26P(2).     

Mate choice in lekking sage grouse revisited: the roles of vocal display, female site fidelity, and copying

In lekking sage grouse (Centrocercus urophasianus), femalesexhibit relatively unanimous mate choice for particular males,but a satisfactory explanation for this unanimity has been elusive.We present analyses of mating distributions from two leks over4 years that provide evidence for female choice based on differencesin vocal display performance of males, the locations at whichhens mated in the previous year, and the choices of other females(copying). The unanimity of female choice varied markedly amongleks and years in correlation with changes in the mean numbersof hens that mated at the same time and hence the opportunityto copy. The results confirm that hens assess phenotypic traitsof males directly but also indicate that the secondary tacticsof site fidelity and copying are often important componentsof female choice. The occurrence of these secondary tacticshas three implications: the variance in mating success amonglek males will be a poor predictor of the intensity of sexualselection on specific traits; female preferences may generatemore clustered dispersions of displaying males than predictedby hotspot settlement models; and direct assessment of malesby females may be difficult or costly, a conclusion that supportsadaptive models of sexual selection over a nonadaptive Fisherianprocess. [Behav Ecol 1991;2:165–180]     

Reproductive challenges of a rare grass,Calamagrostis porteri subsp. insperata (Swallen) C. Greene: implications for habitat restoration

Background: Habitat management for reproductively challenged rare species is a problem when there is insufficient knowledge of their autecology. This study investigated reproductive failure in the rare grass Calamagrostis porteri ssp. insperata (Swallen) C. Greene (Reed bentgrass). Does the management recommendation of high light stimulate clonal growth, flowering, and seed production? Location: Shawnee National Forest, IL, USA, and in a greenhouse and an experimental garden at Southern Illinois University, Carbondale, IL, USA. Methods: Clones obtained from the three known Illinois populations were grown in a glasshouse under experimental light and soil moisture treatments. After 3 years, plants from the high light treatment were planted outside in an experimental garden where the light treatments were maintained for two more years. In the field, vegetative and flowering tiller density, canopy cover, and associated biotic and abiotic variables including abundance of co‐occurring plant species were monitored for 5 years. The overhead tree canopy was cleared over a portion of one population. Results: In the glasshouse, plants increased in size under high light and moist soil, and there were size differences among populations. Sixty‐six per cent (20 of 30) of the genets flowered when planted outdoors under full sunlight but did not produce seed. In the field, flowering only occurred in Calamagrostis growing in the cleared area, but no seed were produced. The plants in the flowering population were smaller than plants in the other two populations. The herbaceous community associated with Calamagrostis in the open diverged from the communities remaining under the shade. Conclusions: This study highlights the difficulty of managing reproductively challenged rare species. Calamagrostis populations can be managed to enhance clonal growth, but establishment of new populations would require translocation of vegetative material as it is highly unlikely that seed can be obtained.