Cloning and characterization of natriuretic peptides from the venom glands of Australian elapids

The venom from Australian elapid snakes contains a complex mixture of polypeptide toxins that adversely affect multiple homeostatic systems within their prey in a highly specific and targeted manner. Included in these toxin families are the recently described venom natriuretic peptides, which display similar structure and vasoactive functions to mammalian natriuretic peptides. This paper describes the identification and detailed comparative analysis of the cDNA transcripts coding for the mature natriuretic peptide from a total of nine Australian elapid snake species. Multiple isoforms were identified in a number of species and represent the first description of a natriuretic peptide from the venom gland for most of these snakes. Two distinct natriuretic peptide isoforms were selected from the common brown snake (Pseudonaja textilis), PtNP-a, and the mulga (Pseudechis australis), PaNP-c, for recombinant protein expression and functional analysis. Only one of these peptides, PtNP-a, displayed cGMP stimulation indicative of normal natriuretic peptide activity. Interestingly, both recombinant peptides demonstrated a dose-dependent inhibition of angiotensin converting enzyme (ACE) activity, which is predictive of the vasoactive effects of the toxin. The natriuretic peptides, however, did not possess any coagulopathic activity, nor did they inhibit or potentiate thrombin, adenosine diphosphate or arachidonic acid induced platelet aggregation. The data presented in this study represent a significant resource for understanding the role of various natriuretic peptides isoforms during the envenomation process by Australian elapid snakes. (c) 2006 Published by Elsevier Masson SAS.

cGMP mediates the vascular and platelet actions of nitric oxide: confirmation using an inhibitor of the soluble guanylyl cyclase.

The L-arginine:nitric oxide (NO) pathway is believed to exert many of its physiological effects via stimulation of the soluble guanylyl cyclase (SGC); however, the lack of a selective inhibitor of this enzyme has prevented conclusive demonstration of this mechanism of action. We have found that the compound 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ) inhibits the elevation of cGMP induced by the NO donor S-nitroso-DL-penicillamine in human platelets and rat vascular smooth muscle (IC50 = 10-60 nM and <10 nM, respectively) and that this is accompanied by prevention of the platelet inhibitory and vasodilator actions of NO donors. ODQ also inhibited the antiaggregatory action of NO generated by the platelets but did not affect the action of prostacyclin or that of a cGMP mimetic. In addition, ODQ inhibited the vasodilator actions of endogenously released NO and of NO generated after induction of NO synthase in vascular preparations. It did not, however, affect the increase in vascular smooth muscle cGMP or the dilatation induced by atrial natriuretic factor. ODQ had no effect on NO synthase activity, nor did it react with NO. It did, however, potently (IC50 approximately 10 nM) inhibit the activity of the SGC in cytosol obtained from crude extract of rat aortic smooth muscle. Thus ODQ prevents the actions of NO on platelets and vascular smooth muscle through its potent inhibitory effect on the SGC.

Enhanced Endothelium-dependent Relaxation Of Rat Pulmonary Artery Following β-adrenergic Overstimulation: Involvement Of The No/cgmp/vasp Pathway.

The aim of this study was to investigate whether β-adrenoceptor (β-AR) overstimulation induced by in vivo treatment with isoproterenol (ISO) alters vascular reactivity and nitric oxide (NO) production and signaling in pulmonary arteries. Vehicle or ISO (0.3mgkg(-1)day(-1)) was administered daily to male Wistar rats. After 7days, the jugular vein was cannulated to assess right ventricular (RV) systolic pressure (SP) and end diastolic pressure (EDP). The extralobar pulmonary arteries were isolated to evaluate the relaxation responses, protein expression (Western blot), NO production (diaminofluorescein-2 fluorescence), and cyclic guanosine 3',5'-monophosphate (cGMP) levels (enzyme immunoassay kit). ISO treatment induced RV hypertrophy; however, no differences in RV-SP and EDP were observed. The pulmonary arteries from the ISO-treated group showed enhanced relaxation to acetylcholine that was abolished by the NO synthase (NOS) inhibitor N(ω)-nitro-l-arginine methyl ester (l-NAME); whereas relaxation elicited by sodium nitroprusside, ISO, metaproterenol, mirabegron, or KCl was not affected by ISO treatment. ISO-treated rats displayed enhanced endothelial NOS (eNOS) and vasodilator-stimulated phosphoprotein (VASP) expression in the pulmonary arteries, while phosphodiesterase-5 protein expression decreased. ISO treatment increased NO and cGMP levels and did not induce eNOS uncoupling. The present data indicate that β-AR overactivation enhances the endothelium-dependent relaxation of pulmonary arteries. This effect was linked to an increase in eNOS-derived NO production, cGMP formation and VASP content and to a decrease in phosphodiesterase-5 expression. Therefore, elevated NO bioactivity through cGMP/VASP signaling could represent a protective mechanism of β-AR overactivation on pulmonary circulation.

Using Reverberation to Improve Range and Elevation Discrimination for Small Array Sound Source Localization

Sound source localization (SSL) is an essential task in many applications involving speech capture and enhancement. As such, speaker localization with microphone arrays has received significant research attention. Nevertheless, existing SSL algorithms for small arrays still have two significant limitations: lack of range resolution, and accuracy degradation with increasing reverberation. The latter is natural and expected, given that strong reflections can have amplitudes similar to that of the direct signal, but different directions of arrival. Therefore, correctly modeling the room and compensating for the reflections should reduce the degradation due to reverberation. In this paper, we show a stronger result. If modeled correctly, early reflections can be used to provide more information about the source location than would have been available in an anechoic scenario. The modeling not only compensates for the reverberation, but also significantly increases resolution for range and elevation. Thus, we show that under certain conditions and limitations, reverberation can be used to improve SSL performance. Prior attempts to compensate for reverberation tried to model the room impulse response (RIR). However, RIRs change quickly with speaker position, and are nearly impossible to track accurately. Instead, we build a 3-D model of the room, which we use to predict early reflections, which are then incorporated into the SSL estimation. Simulation results with real and synthetic data show that even a simplistic room model is sufficient to produce significant improvements in range and elevation estimation, tasks which would be very difficult when relying only on direct path signal components.

North-West elevation, C House, Cooparoo, Brisbane

Entry stair in foreground.

North-West elevation, C House, Coorparoo, Brisbane

As seen from pool deck, looking towards The Nest. Kitchen skylight above right.

North-West elevation, C House, Coorparoo, Brisbane

Upper level of North-West elevation, kitchen skylight on left.

North-West elevation, C House, Coorparoo, Brisbane

As seen from pool deck. Concrete framework for The Nest on left.

North-West elevation, C House, Coorparoo, Brisbane

As seen from car parking area.

North-West elevation, C House, Coorparoo, Brisbane

As seen from pool deck.

Street elevation, Q House, Chelmer, Brisbane

View to house from street. Existing house gable roof on right.

West elevation, General Purpose North 3, University of Queensland, St Lucia

Formal elevation facing University of Queensland entrance roads.

West elevation, General Purpose North 3, University of Queensland, St Lucia

Formal elevation facing University of Queensland entrance roads.