Effects of black widow spider venom on acetylcholine release from Torpedo electric tissue slices and subcellular fractions in vitro

alpha-latrotoxin is a potent inducer of neurotransmitter release in Torpedo electric organ--functional and morphological characterization

In this report we show that alpha-latrotoxin from black widow spider venom is a potent activator of neurotransmitter release in synaptosomes from the Torpedo electric organ. Binding of the purified toxin (5 nM) to the synaptosomal fraction occurs already at 4 degrees C and is dependent on the presence of divalent ions. However, neurotransmitter release commences only after temperature elevation (22 degrees C) and is completed within 2 min. The effect of alpha-latrotoxin on release is achieved at 1 nM and is already saturated at 5 nM. The release is stimulated by the presence of Ca2+ ions. Activation of release by alpha-latrotoxin is accompanied by morphological changes in electric organ synaptosomes. The synaptosomes swell, resulting in a 55% increase in section area. Moreover, the number of synaptic vesicles per unit area decreases about three-fold, and rows of docked synaptic vesicles are rarely detected as opposed to control synaptosomes. These morphological changes indicate that the massive release is mainly due to synaptic vesicle fusion. alpha-Latrotoxin binding sites are highly concentrated in the innervated face of the electrocytes. Immunoelectron microscopy on electric organ sections reveals alpha-latrotoxin binding sites over the entire plasma membrane at release sites and facing Schwann cells surrounding Torpedo nerve terminals. Surprisingly, a high concentration of binding sites is also found at structures surrounding branching unmyelinated axons. This staining is in close proximity to Schwann cell envelopes and to the basal lamina around axonal tips. The mode of action of alpha-latrotoxin in view of the localization of its binding sites is discussed.

Alpha-latrotoxin and glycerotoxin differ in target specificity and in the mechanism of their neurotransmitter releasing action

alpha-Latrotoxin, a high molecular weight protein (130,000) purified from the venom of the black widow spider, and a partially purified neurotoxin, glycerotoxin, prepared from extracts of the jaw glands of the polichaete annelid Glycera convoluta, were previously found to induce similar effects (stimulation of quantal acetylcholine release) at the frog neuromuscular junction. In the present study parallel experiments performed with these two toxins revealed that only glycerotoxin was able to release acetylcholine from Torpedo electric organ synaptosomes, while alpha-latrotoxin did not affect release in this system. In contrast, alpha-latrotoxin stimulated release of dopamine from PC12 cells (a cloned neurosecretory cell line), whereas glycerotoxin was almost inactive. In rat brain synaptosomes both toxins were active. Preincubation of synaptosomal membranes with glycerotoxin was without effect on the subsequent binding of alpha-latrotoxin. Glycerotoxin application induced depolarization of synaptosomal plasma membrane, massive Ca2+ influx, marked increase of the cytosolic Ca2+ concentration, and stimulation of catecholamine release. The latter effect occurred to the same extent when glycerotoxin was applied either in complete medium (containing both Ca2+ and Mg2+), Ca2+-free medium or divalent cation-free medium. Some of these effects of glycerotoxin in rat brain synaptosomes (depolarization, increased Ca2+ influx and increased cytosolic Ca2+ concentration) resemble effects previously reported for alpha-latrotoxin. However, the secretory response induced by the latter was reduced in Ca2+-free, and abolished in divalent cation-free media. The different target specificity and the lack of binding competition of the two toxins could be due to their ability to recognize different receptors whose distribution overlap only in part in the cellular systems we have studied. The differences in action, on the other hand, could depend on postreceptor events, possibly related to the transmembrane insertion of toxin molecules demonstrated by others in artificial lipid membranes.

Hydrolysis of substance P and bradykinin by black widow spider venom gland extract

Black widow spider venom gland extract was found to contain significant peptidase activity. Aliquots of the venom gland extract incubated at 37 degrees inactivated substance P (SP) and bradykinin but not angiotensin II or the enkephalins. The peptide inactivation was proportional to the duration of the incubation and the amount of extract used. Analysis of the peptides on high pressure liquid chromatography demonstrated that the loss in biological activity of SP and bradykinin in the longitudinal muscle of the guinea pig ileum was correlated with cleavage of the peptides into several fragments. Kinetic studies revealed that SP was initially split into two fragments but that these products underwent further degradation into smaller peptides. The optimal pH for the peptidase activity was 6.5. At 0 degree the enzymatic activity was undetectable, and it was irreversibly destroyed by incubation at 100 degrees for 5 min or by pretreatment of the extract with 100 microM diisopropyl fluorophosphate. In addition, the gland extract preparation hydrolyzed artificial substrates designed to detect trypsin or chymotrypsin-like activity.

Effect of the venom of Glycera convoluta on the spontaneous quantal release of transmitter

A neurotoxin able to increase the spontaneous release of transmitter was found in the venom glands of the polychaete annelid Glycera convoluta. We studied the effect of this venom on the frog cutaneous pectoris muscle, where its application produced a prolonged (20-h), high-frequency discharge of miniature potentials. After 5 h of action, the initial store was renewed several times but no detectable ultrastructural changes were observed. After 19 h of sustained activity, nerve terminals with their normal vesicular contents were infrequent; others were fragmented and contained swollen mitochondria, abnormal inclusions, and vesicles of various sizes. In the noncholinergic crayfish neuromuscular preparation, the venom triggered an important increase in spontaneous quantal release that subsided in 1 h. An activity higher than that in resting conditions then persisted for many hours. This high electrical activity was not accompanied by any detectable structural modifications after 3 h. In the torpedo electric organ preparation, the venom elicited a burst of activity that returned to control levels in 1 h. The release of ACh (evaluated by the efflux of radioactive acetate) paralleled the high electrical activity. No morphological changes or significant depletion of tissue stores were detected. The venom of Glycera convoluta appears to enhance considerably the release of transmitter without impairing its turnover. The venom effect is Ca++ dependent and reversible by washing, at least during the first hour of action. Because the high rate of transmitter release appears dissociated from the later-occurring structural modifications, it is possible that the venom mimics one component of the double mode of action proposed for black widow spider venom.

Purification from black widow spider venom of a protein factor causing the depletion of synaptic vesicles at neuromuscular junctions

The aqueous extract of the venom glands of black widow spiders was fractionated on a column of Sephadex G-200 and then on a column of DEAE-Sephadex A-50 pH 8.2. A protein fraction was obtained that caused a great increase in the frequency of occurrence of miniature end plate potentials at the frog neuromuscular junction, and caused swelling of the nerve terminals and depleted them of their vesicles. The fraction consists of a least four protein components that are similar in their molecular weights (about 130,000) and isoelectric points (ranging from pH 5.2 to 5.5) and are immunologically indistinguishable. It contains no sugar residues and has little or no lipolytic or proteolytic activity. The fraction is toxic to mice and is different from the fractions that act on houseflies, the crayfish stretch receptor and the cockroach heart. It seems pure enough to warrant a detailed study of its site and mode of action.