Avner Bdolah

Sarafotoxins S6: several isotoxins from Atractaspis engaddensis (burrowing asp) venom that affect the heart.

Three isotoxins, named sarafotoxins S6a1, S6b and S6c, with strong cardiotoxic activity were isolated from the venom of a snake, Atractaspis engaddensis. All three sarafotoxins are homologous peptides (four or less than four residue replacements) consisting of 21 amino acid residues. Their structure and activity are novel among snake venom components.

Three apparent receptor subtypes for the endothelin/sarafotoxin family

Competition binding experiments performed with 125I‐sarafotoxin (SRTX)‐b and SRTX‐b, SRTX‐c and endothelin (ET‐1 and ET‐3) using homogenates of rat right and left atria, aorta, uterus, cerebellum and caudate putamen indicated heterogeneity of the ET/SRTX receptor. The evidence pointed to the existence of three receptor subtypes: a high‐affinity ET‐1/SRTX‐b subtype typical of smooth muscle (E‐Sα receptor), a high‐affinity SRTX‐c subtype typical of the cerebellum (E‐Sβ receptor), and a less selective subtype typical of the caudate putamen that binds all of these peptides with high affinity (E‐Sγ receptor).

A novel cardiotoxic polypeptide from the venom of Atractaspis engaddensis (burrowing asp): Cardiac effects in mice and isolated rat and human heart preparations

A new cardiotoxic polypeptide isolated from the venom of the snake Atractaspis engaddensis has an LD50 of 15 micrograms/kg body weight in white mice. Intravenous administration in mice of lethal doses of the toxin causes, within seconds, marked changes in the ECG, consisting primarily of a transient slope elevation of the S-T segment, a temporary diminution of the S-wave and an increase in the amplitudes of the R- and T-waves. Concomitantly, and apparently unrelated to these changes, a severe A-V block develops and leads to complete cardiac arrest within a few min. Studies with rat and human isolated heart preparations showed that the toxin exerts a powerful coronary vasoconstriction (rats), and positive inotropic effects (rats and humans).

SRTX-d, a new native peptide of the endothelin/sarafotoxin family

Sarafotoxin; Endothelin; Snake venom; Aorta

Sarafotoxins and endothelins: evolution, structure and function☆

The venom of the burrowing asp Atractaspis engaddensis contains several 21 amino acid residue peptides known as sarafotoxins. The sarafotoxins are homologous to the mammalian endothelin family, and they have similar biological activities. This review covers recent advances in the study of the chemical and biological properties of the sarafotoxins and endothelins.

Functional endothelin/sarafotoxin receptors in the rat uterus

Functional receptors for the peptides of the endothelin (ET) and sarafotoxin (SRTX) families were detected in the rat uterus. These receptors specifically bind 125I-SRTX-b (Bmax = 220 fmol/mg protein), as well as ET-1, ET-3 and SRTX-c (IC50s 10, 5, 300 and 780 nM, respectively). Activation of the uterine ET/SRTX receptors induced dose-dependent phosphoinositide (PI) hydrolysis and three typical contractile responses: 1) increase in the muscle tonic tension; 2) increase in frequency of the spontaneous rhythmic contractions; 3) decrease of relaxation in each spontaneous rhythmic cycle. All three effects appeared at doses as low as 0.5-1 nM. Dose responses yield ED50 values of 5.5, 30 and 680 nM for ET-1, SRTX-b and ET-3, respectively. SRTX-c was the least effective peptide in achieving decrease in relaxation. In view of these results, and since the uterine responses to the peptides were almost immediate and reversible, we suggest that the functional ET/SRTX receptor of the rat uterus that is coupled to PI hydrolysis may be of physiological significance.

Functional endothelin/sarafotoxin receptors in rat heart myocytes: Structure-activity relationships and receptor subtypes

Functional receptors for the peptides of the endothelin (ET) and sarafotoxin (SRTX) family were characterized in newborn rat heart myocytes using human and rat endothelins (ET-1 and ET-3, respectively), SRTX-b and SRTX-c. Binding studies in intact cells and homogenates revealed significantly higher affinities of ET-1 and SRTX-b than of ET-3 and SRTX-c towards these receptors. This binding profile of ET/SRTX peptides points to their interaction with the receptor subtype designated E-S alpha. All four peptides induced time- and dose-dependent phosphoinositide hydrolysis with the following rank order of potency: ET-1 greater than SRTX-b greater than SRTX-c greater than ET-3. Thus, ET-3 which possesses an intermediate affinity toward the receptor was the least effective with regard to this response. These results confirm and extend our earlier report that the ET/SRTX peptides interact with a newly characterized receptor(s) associated with phosphoinositide metabolism and Ca2+ mobilization. The initiation of inositol phosphate formation is largely independent of extracellular Ca2+, verapamil and nifedipine, indicating that the ET/SRTX peptides are not agonists for the voltage-dependent Ca2+-channels.

The mechanism of enzyme secretion by the cell: II. Secretion of amylase and other proteins by slices of rat parotid gland***

Rat parotid gland slices in Krebs-Ringer bicarbonate medium secrete amylase and DNase at an enhanced rate in response to epinephrine. A high potassium concentration (60 m M ) effectively replaced epinephrine as a stimulant of secretion. The process was dependent on oxygen, was inhibited by DNP and cyanide, but not by inhibitors of glycolysis. When epinephrine was the stimulant, secretion was also dependent on a minimal concentration of potassium (5 m M ). Slices lost 90% of their potassium content in 75 minutes when incubated in a medium free of this ion. Once exhausted of potassium the slices no longer showed enhanced enzyme secretion when epinephrine was added. Other ions of the Krebs-Ringer bicarbonate medium did not appear essential for protein secretion. Amylase was secreted at a constant specific activity throughout an incubation of 3 hours when 78% of the enzyme and 53% of the total protein of the slice appeared in the medium. During early periods of incubation the amount of enzyme secreted into the medium was equivalent to the amount lost from the intracellular zymogen granules. Loss of amylase from the soluble supernatant fraction of the slice was observed only after the zymogen granules had released about 80% of their initial amylase content. The number of granules appeared to remain almost constant during secretion although their size and contrast was changed. It is therefore tentatively concluded that only the contents of the granules are transported out of the cell.

The two-component toxin of Vipera palaestinae: Contribution of phospholipase A to its activity

The heat stable toxic fraction of Vipera palaestinae venom contains a basic (pI 10) non-enzymic component and an acidic (pI 4·5) phospholipase A. The purified phospholipase appears as a single protein band in SDS-gel electrophoresis corresponding to a mol. wt of 15,000. An antitoxic factor previously isolated from the blood serum of Vipera palaestinae inhibits both lethality of the toxic fraction and phospholipase activity of the acidic component. Heterologous phospholipases from the venoms of Pseudocerastes fieldi and Walterinnesia aegyptia, but not from the porcine pancreas could be substituted for the original enzyme in the Vipera two-component toxic system. It is thus evident that phospholipase is an integral part of the V. palaestinae toxin, and it is either species- or organ-specific.

Sarafotoxin receptors mediate phosphoinositide hydrolysis in various rat brain regions.

Sarafotoxin‐b, a potent snake vasoconstrictor peptide homologous to the mammalian endothelial vasoconstrictor endothelin, induces phosphoinositide (PI) hydrolysis in various brain regions of the rat. Sarafotoxin‐b induced PI hydrolysis is largely independent of extracellular Ca2+ and is detected in all brain regions where toxin‐binding sites are found. These results point to the existence of a hitherto undetected neuroreceptor associated with the PI cycle.