Validation of the doubly labeled water method under low and high humidity to estimate metabolic rate and water flux in a tropical snake (Boiga irregularis).
(33/507)
This study uses indirect calorimetry to assess the effects of humidity on the accuracy of the doubly labeled water (DLW) technique to predict metabolic rate and water flux in brown treesnakes (Boiga irregularis). The DLW technique accurately predicted total water efflux in brown treesnakes under low-humidity conditions and found that the total number of water molecules exchanged with the environment under humid conditions was not significantly different than maximum net total evaporative water loss under low humidity conditions plus fecal water loss. Because of changes of total body water of >12%, the DLW technique overestimated metabolic rate by a factor of 2.2 under low-humidity conditions. Under high-humidity conditions, the DLW technique overestimated metabolic rate in brown treesnakes by a factor of 4.6. Researchers using the DLW technique in humid or moist environments should be cautious because this study indicates that DLW estimates of metabolic rate may be inflated when large amounts of water vapor are exchanged through the skin or respiratory passages. (+info)
Reproductive strategies in snakes.
(34/507)
Snakes of both sexes display remarkable flexibility and diversity in their reproductive tactics. Many features of reproduction in female snakes (such as reproductive mode and frequency, seasonality and multiple mating) allow flexible maternal control. For example, females can manipulate not only the genotypes of their offspring (through mate choice or enhanced sperm competition) but also the phenotypes of their offspring (through allocation 'decisions', behavioural and physiological thermoregulation, and nest-site selection). Reliance on stored energy ('capital') to fuel breeding results in low frequencies of female reproduction and, in extreme cases, semelparity. A sophisticated vomeronasal system not only allows male snakes to locate reproductive females by following scent trails, but also facilitates pheromonally mediated mate choice by males. Male-male rivalry takes diverse forms, including female mimicry and mate guarding; combat bouts impose strong selection for large body size in males of some species. Intraspecific (geographical) variation and phenotypic plasticity in a wide array of reproductive traits (offspring size and number; reproductive frequency; incidence of multiple mating; male tactics such as mate guarding and combat; mate choice criteria) provide exceptional opportunities for future studies. (+info)
Comparison of carbohydrate moieties of sparganum proteins of the snake, mouse and those of adult worm.
(35/507)
The carbohydrate moieties of larval sparganum proteins in two different species, the snakes, Elaphe rufodorsata, the Balb/c mouse and those of the adult worm, Spirometra erinacei, were compared using five different lectins including GNA, SNA, MAA, PNA and DSA. The GNA positive 53 kDa molecule, which is excretory-secretory protease in the sparganum from the snake showed a stage specific and developmental regulation. We also suggested that sparganum glycosylation may be involved in immune evasion and differentiation into an adult worm. (+info)
Proton-nuclear-magnetic-resonance study of the conformation of neurotoxin II from Middle-Asian cobra (Naja naja oxiana) venom.
(36/507)
A proton nuclear magnetic resonance (NMR) study at 100 and 300 MHz of neurotoxin II from the venom of Middle-Asian cobra Naja naja oxiana has been performed in 2H2O and H2O solutions. By means of chemical modification and double resonance all the aromatic residue resonances have been assigned. From the NMR titration curves, pK values of histidine 4 and histidine 31 residues have been determined. For one of the two neighbouring tryptophan residues pH dependence (in the 2-8-pH range) of the chemical shifts of indole protons has been revealed. According to the different sensitivity of the linewidth of indole NH resonances to pH in H2O solution, the accessibility of each of the tryptophan residues has been estimated. Temperature dependence has been observed for the linewidth of the aromatic resonances of the tyrosine 24 residue. Deuterium exchange rates have been measured for amide protons as well as for C(2)H histidine resonances. The NMR data obtained have allowed the conclusions to be made that the two histidine residues and one of the tryptophan residues should be localized on the surface of the protein globule, that arginine residues should be present in the environment of histidine 4, that histidine 31 and the buried tryptophan are possibly localized in close spatial proximity and that the side chain of tyrosine 24 is buried within the protein globule. (+info)
Amino acid sequence of fibrolase, a direct-acting fibrinolytic enzyme from Agkistrodon contortrix contortrix venom.
(37/507)
The complete amino acid sequence of fibrolase, a fibrinolytic enzyme from southern copperhead (Agkistrodon contortrix contortrix) venom, has been determined. This is the first report of the sequence of a direct-acting, nonhemorrhagic fibrinolytic enzyme found in snake venom. The majority of the sequence was established by automated Edman degradation of overlapping peptides generated by a variety of selective cleavage procedures. The amino-terminus is blocked by a cyclized glutamine (pyroglutamic acid) residue, and the sequence of this region of the molecule was determined by mass spectrometry. Fibrolase is composed of 203 residues in a single polypeptide chain with a molecular weight of 22,891, as determined by the sequence. Its sequence is homologous to the sequence of the hemorrhagic toxin Ht-d of Crotalus atrox venom and with the sequences of two metalloproteinases from Trimeresurus flavoviridis venom. Microheterogeneity in the sequence was found at both the amino-terminus and at residues 189 and 192. All six cysteine residues in fibrolase are involved in disulfide bonds. A disulfide bond between cysteine-118 and cysteine-198 has been established and bonds between cysteines-158/165 and between cysteines-160/192 are inferred from the homology to Ht-d. Secondary structure prediction reveals a very low percentage of alpha-helix (4%), but much greater beta-structure (39.5%). Analysis of the sequence reveals the absence of asparagine-linked glycosylation sites defined by the consensus sequence: asparagine-X-serine/threonine. (+info)
Regulation of single quantal efficacy at the snake neuromuscular junction.
(38/507)
1. Postsynaptic responses to spontaneous quantal transmitter release have been compared among neuromuscular junctions in a thin snake muscle. For each junction the type, diameter, and input conductance, G(in) of the postsynaptic muscle fibre were determined. Particularly among fibres of a given type, G(in) was directly correlated with fibre diameter. 2. Miniature endplate potentials (MEPPs) were recorded intracellularly near endplates visualized with Nomarski optics. Mean MEPP amplitude decreased with increasing G(in) among fibres in one muscle. However, the dependence of mean amplitude upon G(in) was not ohmic, as would be expected if the underlying single quantal currents (miniature endplate currents, MEPCs) were of similar amplitude at all junctions. Instead, the relation between MEPPs and G(in) suggested that mean MEPC amplitudes, calculated as mean MEPP amplitude x G(in), increased with increasing G(in). 3. MEPCs were recorded directly using the two-microelectrode voltage clamp technique. Mean MEPC amplitudes depended systematically on G(in), again such that MEPCs were on average larger in fibres with higher G(in). 4. MEPCs were recorded extracellularly from small regions of endplates (underlying a few nerve terminal boutons). Amplitudes of MEPCs depended on G(in) or fibre diameter in the same manner as amplitudes of MEPCs recorded by intracellular voltage clamp. 5. When the anticholinesterase agent neostigmine was added to the bath, amplitude and duration of MEPPs, MEPCs, and extracellular MEPCs increased. However, the systematic dependence of mean MEPC amplitude on G(in) or fibre diameter remained. 6. Evoked subthreshold endplate potentials (EPPs) were recorded under conditions of low extracellular Ca2+. Endplate currents (EPP amplitudes x G(in)) were systematically larger in fibres with larger G(in), indicating regulation of evoked synaptic current in the muscle. The regulation was found to be due to a combination of increased quantal content and larger single quantal currents in larger (higher G(in)) fibres. 7. Synaptic size, assessed either by area of cholinesterase staining or number of terminal boutons, increased with increasing fibre diameter. Assuming that quantal content is proportional to synaptic size, this relation was sufficient to account for the observed increase in quantal content with increasing G(in) among fibres in the muscle, but was not alone sufficient to account for the observed regulation of evoked current. 8. It is concluded that the efficacy of individual transmitter quanta released at the snake neuromuscular junction is regulated such that large muscle fibres receive larger single quantal currents. Regulation of single quantal current contributes substantially to overall regulation of synaptic strength in the muscle. (+info)
A new member of the natriuretic peptide family is present in the venom of the green mamba (Dendroaspis angusticeps).
(39/507)
This paper describes the purification, sequence, and biological properties of a 38-amino acid residue peptide from the venom of Dendroaspis angusticeps which shared important sequence homologies with natriuretic peptides. Dendroaspis natriuretic peptide (DNP) relaxed aortic strips that had been contracted by 40 mM KCl with a potency (K0.5 = 20 nM) similar to that of atrial natriuretic peptide (ANP) and larger than that of C type natriuretic peptide (CNP). The relaxing actions of ANP and DNP (both at 100 nM) were mutually exclusive. Bovine aortic endothelial cells responded to ANP (K0.5 = 3 nM) and DNP (K0.5 = 3 nM) but not to CNP by a large activation of guanylate cyclase. Rat aortic myocytes showed larger cGMP responses to CNP (K0.5 = 10 nM) than to ANP or DNP (K0.5 = 100 nM). Finally, DNP completely prevented the specific 125I-ANP binding to clearance receptors in cultured aortic myocytes with a potency (Kd = 10 nM) that was less than that of ANP (Kd = 0.3 nM). It is concluded that DNP is a new member of the family of natriuretic peptides and that it recognizes ANPA receptors and clearance, ANPc receptors, but not CNP-specific ANPB receptors. (+info)
The innervation of muscle spindles in the snake, Elaphe quadrivirgata.
(40/507)
The morphology and distribution of sensory endings in snake (Elaphe quadrivirgata) muscle spindles was studied in silver preparations. The sensory axon supplying long-capsule spindles often bifurcates before or after penetrating the capsule and runs for some distance along the intrafusal fibre. The sensory axon supplying short-capsule spindles penetrates the capsule at a sharp angle, and, without ramification, terminates abruptly on the intrafusal fibre. The sensory terminal is composed of terminal bulbs and small links. In long-capsule spindles the sensory ending is arranged longitudinally in one or two rows. The sensory ending in short-capsule spindles ramifies extensively, covering densely the intrafusal fibre. The area occupied by sensory bulbs was estimated to be slightly higher in short-capsule (15-17?) THAN IN LONG-CAPSULE SPINDLES (12-13). The functional significance of these findings is discussed. Motor innervation of muscle spindles in the snake Elaphe quadrivirgata was studied using AchE staining for light microscopy in conjection with electron microscopy. In the polar region of either type of spindle, the majority of the motor endings are of grape type. In long-capsule spindles plate endings may occur in the spindle pole as well as in the capsular region. Motor endings in the capsular region are mostly of plate type. Plate endings rarely occur in short-capsule spindles. Identified single motor endings were studied by electron microscopy. Intrafusal grape endings are characterized by a smooth post-synaptic membrane. Intrafusal plate endings in the polar region are characterized by junctional folds or gutterings; plate endings in the capsular region show less developed gutterings or indentations. The distribution of intrafusal motor endings was examined along the length of single intrafusal fibres. The long-capsule spindle often receives asymmetrical motor innervation around the capsular region, whereas motor endings in the short-capsule spindle distribute more symmetrically. (+info)