CONVULXIN, A NEW TOXIN FROM THE VENOM OF THE SOUTH-AMERICAN RATTLESNAKE CROTALUS-DURISSUS-TERRIFICUS

196875

LIPOXYGENASE-DERIVED MEDIATORS MAY BE INVOLVED IN IN-VIVO NEUTROPHIL MIGRATION INDUCED BY BOTHROPS ERYTHROMELAS AND BOTHROPS ALTERNATUS VENOMS

Bothrops erythromelas (BEV) and B. alternatus (BAV) venoms induced a dose-dependent neutrophil migration when injected into rat peritoneal cavities (20-160 mu g/cavity). These venoms (80 mu g/rat) also induced neutrophil migration in the air pouch model of inflammation. This migratory response seemed to be related to the phospholipase A(2) (PLA(2)) activity of the venoms. BAV had approximately two times more PLA(2) activity than BEV, and the neutrophil migration induced by the former venom was two to three-fold greater than that observed with the latter. Heated (90 degrees C for 5 min) BEV lost about 50% of its PLA(2) activity and this was accompanied by a corresponding loss in the ability to induce neutrophil chemotaxis. Dexamethasone (0.5 mg/kg, s.c.), an indirect inhibitor of PLA(2) activity, also abolished the neutrophil migration induced by both venoms. Since NDGA (100 mg/kg, s.c.) and dexamethasone, but not indomethacin (2 mg/kg, s.c.), strongly reduced the neutrophil migration induced by both bothropic venoms, it is suggested that arachidonate-derived lipoxygenase metabolites such as leukotriene B-4 act as the chemotactic mediators. Macrophages could be the main cellular source of such metabolites since they are the predominant resident cells in the rat air pouch, and the migratory response of BEV and BAV into peritoneal cavities was potentiated in rats pretreated with thioglycollate. The neutrophil migration induced by BEV and BAV was not due to endotoxin contamination since heated BEV showed no effect and polymyxin B-treated BAV still remained active.31121551155

EFFECTS OF CONVULXIN, A TOXIN FROM RATTLESNAKE VENOM, ON PLATELETS AND LEUKOCYTES OF ANESTHETIZED RABBITS

19566166

CONVULXIN DOES NOT INDUCE CONVULSIONS WHEN INJECTED INTO THE RAT DORSAL HIPPOCAMPUS

39435335

EFFECT OF BOTHROPS-INSULARIS VENOM ON THE MOUSE AND CHICK NERVE-MUSCLE PREPARATION

The effects of Bothrops insularis venom were examined in vivo in mice and chicks and in vitro using the mouse phrenic nerve diaphragm and chick biventer cervicis muscle preparations. Incubation of the indirectly or directly stimulated mouse preparation with B. insularis venom (20-80 mug/ml) produced an initial increase in twitch tension followed by irreversible blockade. With direct stimulation in the presence Of D-tubocurarine, no increase in twitch tension was observed prior to the onset of blockade. A venom-induced effect on presynaptic activity was suggested by the marked increase in the frequency of the mepps recorded in vitro 5-15 min after venom addition. A direct muscular effect was shown by the dose- and time-dependent reduction in the resting membrane potential of the diaphragm. Chick preparations were more sensitive than those of the mouse. In the isolated chick biventer cervicis muscle preparation, B. insularis venom induced a contracture and a dose-dependent block of responses to indirect stimulation. At low venom concentrations (1-5 mug/ml), no significant release of creatine kinase (CK) was observed from this preparation. However, a dose-dependent release of CK was detected at higher doses (10-80 mug/ml). For morphological studies, B. insularis venom was injected into the chick left pectoralis muscle. At low doses (0.4 mug), only an inflammatory reaction was present, while at high doses (20-80 mug) increasing numbers of necrotic fibers were observed as well as occlusive thrombosis and hemorrhage. The muscular effect, also observed on the incubated muscle, points to a direct myolytic action of the whole venom.31101237124

Landbrugstoldkommissionens Flertalsbetænkning.

The role of low levels of phospholipase A(2) (PLA(2)) activity and intracellular Ca2+ stores in the pharmacological action of bothropstoxin (BthTX), a myotoxic Lys49 PLA(2) homologue isolated from the venom of Bothrops jararacussu, was investigated. We examined the muscular effects of BthTX in the mouse diaphragm and its PLA, activity in radiolabeled human and rat primary cultures of skeletal muscle. Although it is a Lys49 PLA(2) homologue, BthTX had a low, but easily detectable, level of enzymatic activity relative to two Asp49 PLA(2) enzymes from Naja naja kaouthia and Naja naja atra venoms, and this activity was reduced by about 85% in the presence of Sr2+ (4.0 mM). However, the replacement of 1.8 mM Ca2+ by 4 mM Sr2+ did not alter the BthTX-induced contracture and blockade of the muscle twitch tension. In addition, Sr2+ decreased by 50% the time required to cause 50% paralysis, and evoked approximately a four-fold increase in the number of spontaneous spikes. In isolated sarcoplasmic reticulum preparations, BthTX opened the intracellular Ca2+ release channel (ryanodine receptor) and lowered the threshold of Ca2+-induced Ca2+ release by a second, as yet unidentified, mechanism. However, in intact muscle, dantrolene, an antagonist of some forms of intracellular Ca2+ release, had no effect on the actions of BthTX. These findings do not support any role for the low levels of PLA(2) activity, or dantrolene-sensitive intracellular Ca2+ stores, in the action of BthTX. The mechanism whereby Sr2+ stimulates the pharmacological activity of BthTX remains to be clarified.33111479148

EFFECTS INDUCED BY BOTHROPSTOXIN, A COMPONENT FROM BOTHROPS-JARARACUSSU SNAKE-VENOM, ON MOUSE AND CHICK MUSCLE PREPARATIONS

Bothropstoxin, a 13,700 mol.wt myotoxic phospholipase homologue isolated from the venom of Bothrops jararacussu and devoid of PLA2, proteolytic or hemolytic activities, inhibited muscle twitch tension, evoked either directly or indirectly through stimulation of the motor nerve in the mouse phrenic-diaphragm preparations. The compound action potential of the muscle was also abolished with a similar time course. In addition, the toxin (0.7 mM) evoked membrane depolarization which was inhibited in the presence of 10 mM Ca2+. In chick biventer cervicis muscle, the toxin (2 mM) induced a contracture that reached its maximum amplitude in 44.8 +/- 15.6 min (n = 6) and was not blocked by either d-tubocurarine or tetrodotoxin. The time to maximum amplitude was reduced to 5.5 +/- 1.0 min (n = 4) in nominally Ca2+-free Krebs solution and was completely abolished in Ca2+-free Krebs solution containing 1 mM EGTA.30101203121

The effects of Duvernoy's gland secretion from the xenodontine colubrid Philodryas olfersii on striated muscle and the neuromuscular junction: Partial characterization of a neuromuscular fraction

The effect of Philodryas olfersii Duvernoy's secretion was studied in vivo in mice and chicks as well as in the mouse phrenic nerve-diaphragm and the chick biventer cervicis preparations. The whole secretion (20-40 mu g/ml) increased the creatine kinase (CK) levels in mice but had no effect on the mouse phrenic nerve-diaphragm preparation, In the chick, the secretion caused head drop and paresia as well as irreversible blockade of the twitch-tension evoked by indirect stimulation in the chick biventer cervicis preparation (50% paralysis in 34.5 +/- 2.7 min, n = 4). The secretion also caused muscle contracture (30% of the maximal twitch-tension generated) after a latency of nearly 9 min. Following fractionation on a Superose 12 FPLC column, the neuromuscular activity was recovered in the high mol, wt fraction (Peak I). At a concentration of 10 mu g/ml in the chick biventer cervicis preparation, Peak I caused 50% paralysis within 18.5 +/- 3.0 min (n = 4), and evoked a strong contracture (70%, of the maximal twitch-tension generated). The contractile responses of the chick preparation to ACh and KCl were partially blocked (90%) by the whole secretion and totally blocked by Peak I. CK release was increased by the whole secretion but not by Peak I. The whole secretion also produced various degrees of muscle cell lysis and extensive widening of the intercellular spaces. The latter showed a loosely arranged membranous network. In general, Peak I caused only minor morphological alterations compared with the whole secretion, although these were still significantly different from those observed in the control preparations. The changes principally involved hypercontraction of the muscle fibers. Based on the above results, we conclude that Peak I contains the factor(s) responsible for the in vitro effects on neuromuscular transmission, whereas the direct myotoxic effect is apparently caused by at least one other component of the Duvernoy's secretion. (C) 1996 Elsevier Science Ltd.34445946

Novel effects of guanidine on the neuromuscular junction

1. The effects of guanidine on the isolated mouse phrenic nerve diaphragm(MPND) and chick biventer cervicis (CBC) neuromuscular preparations were determined by myographic and electrophysiological methods. 2. Guanidine at concentrations of 5-10 mM induced an initial facilitation followed by neuromuscular blockade in both preparations. In the isolated MPND such blockade was associated with the abolition of miniature end-plate potentials (MEPPs), but in the CBC the acetylcholine-induced contracture remained unimpaired. After guanidine removal, a heretofore undescribed pronounced facilitation of neuromuscular transmission associated with an increase in MEPP frequency was observed. Simultaneously, the muscular contractions exhibited delayed relaxation and aftercontractions. 3. The K+ channel opener, cromakalim (100-200 mu M) inhibited both the well-described initial and the novel postremoval facilitatory effects of guanidine in a concentration-dependent manner. These findings are consistent with the proposal that guanidine blocks K+ channels in motor nerve endings. 4. The guanidine-induced NMB was reverted by increasing the Ca2+ concentration (1.8-5 mM) in the nutritive solution. 5. Tetrodotoxin (TTX, 1.56 mu M) did not influence the increase in MEPPS frequency induced by guanidine (10 mM) but did reduce the rise in MEPPS frequency observed after guanidine removal. 6. The present findings indicate that the effects of guanidine on the neuromuscular junction are more complex than currently described because they include a neuromuscular blockade and a postremoval facilitation previously unreported in the literature. (C) 1997 Elsevier Science Inc.28459960