Pharmacological effects of two cytolysins isolated from the sea anemone Stichodactyla helianthus.

Sticholysins I and II (St I/II) are cytolysins purified from the sea anemone Stichodactyla helianthus. In this study, we show their pharmacological action on guinea-pig and snail models in native and pH-denatured conditions in order to correlate the pharmacological findings with the pore-forming activity of both isoforms. In guinea-pig erythrocytes (N=3), St II possessed higher haemolytic activity in comparison with St I and this activity was lost at an alkaline pH. In molluscan central neurons (N=30), they irreversibly decreased the amplitude of the cholinergic response; St I (EC (50) 0.6 micromolL (-1)) was more potent than St II (EC50 > 6.6 micromolL (-1)) and they both increased the duration of the action potential; these effects were absent at an alkaline pH. In guinea-pig isolated atrium (N=25), both increased the amplitude of the contraction force, but St II was more potent than St I (EC (50) 0.03 micromolL (-1) and 0.3 micromolL (-1), respectively) and this effect persisted at an alkaline pH. In summary, both cytolysins have neuroactive and cardioactive properties. The main mechanism in molluscan neurons seems to be associated with the cytolytic activity of these molecules, whereas inguinea-pig atrium, the existence of an additional pharmacological mechanism might be contributing to the observed effect.

Pharmacological effects of two cytolysins isolated from the sea anemone Stichodactyla helianthus

Sticholysins I and II (St I/II) are cytolysins purified from the sea anemone Stichodactyla helianthus. In this study, we show their pharmacological action on guinea-pig and snail models in native and pH-denatured conditions in order to correlate the pharmacological findings with the pore-forming activity of both isoforms. In guinea-pig erythrocytes (N=3), St II possessed higher haemolytic activity in comparison with St I and this activity was lost at an alkaline pH. In molluscan central neurons (N=30), they irreversibly decreased the amplitude of the cholinergic response; St I (EC (50) 0,6 micromolL (-1)) was more potent than St II (EC50 > 6,6 micromolL (-1)) and they both increased the duration of the action potential; these effects were absent at an alkaline pH. In guinea-pig isolated atrium (N=25), both increased the amplitude of the contraction force, but St II was more potent than St I (EC (50) 0,03 micromolL (-1) and 0,3 micromolL (-1), respectively) and this effect persisted at an alkaline pH. In summary, both cytolysins have neuroactive and cardioactive properties. The main mechanism in molluscan neurons seems to be associated with the cytolytic activity of these molecules, whereas inguinea-pig atrium, the existence of an additional pharmacological mechanism might be contributing to the observed effect(AU)

BgK anemone toxin inhibits outward K(+) currents in snail neurons.

We studied the effects of BgK toxin on outward K(+) currents in isolated neurons of the snail Helix aspersa, using the whole cell patch clamp technique. BgK partially and reversibly blocked K(+) currents in the 1 pM to 100 nM concentration range (n=53). The dose-response curve for BgK current inhibition had a maximum blocking effect at 100 nM. Our results indicate that BgK is a potent, apparently non-selective, K(+) channel blocker in molluscan neurons.

Effects of a toxin from the mucus of the Caribbean sea anemone (Bunodosoma granulifera) on the ionic currents of single ventricular mammalian cardiomyocytes.

The effects were studied of a toxin (Bainh) isolated from the secretion of the Caribbean sea anemone Bunodosoma granulifera on electrical and mechanical activities of rat ventricular muscle. The effects on the ionic currents of single rat and dog ventricular cardiomyocytes were studied using the whole-cell recording patch-clamp technique. In the concentration range from 1 to 10 mg/ml, Bainh increased the force of contraction and induced an increase in action potential duration of ventricular multicellular preparations. In single cardiomyocytes, at concentrations up to 10 mg/ml Bainh showed no significant effects on the sodium current. However, at 0.5-1 mg/ml it increased the L-type Ca current (ICaL) by 25-50%. This increase in ICaL was not voltage dependent and was reversible after washout. The transient outward current was not significantly affected by Bainh (1-10 mg/ml). In this concentration range, Bainh markedly (approximately 75%) increased the inward-going rectifier current, IKI. This effect that was not voltage dependent and was fully reversible upon returning to control solution. It is suggested that these effects on ionic currents could explain the positive inotropic action of Bainh on cardiac multicellular preparations.

Antagonism of glutamate receptors by a chromatographic fraction from the exudate of the sea anemone Phyllactis flosculifera.

In the search for new glutamate antagonists it seems promising to characterize the effects of venom from invertebrates that prey mainly on crustaceans. In this work, the exudate of the sea anemone Phyllactis flosculifera was used as a source of this type of compound. The action of chromatographic fraction D from P. flosculifera was tested upon microion-tophoretically evoked glutamate responses in intracellular recordings from central neurons of the land snail Zachrysia guanensis. Bath application of fraction D (2-8 mg/ml, n = 13) diminished both the excitatory and the inhibitory components of glutamate agonists in Z. guanensis neurons; this action was dose-dependent and partially reversible. Fraction D actions were also tested in the multiunit spontaneous and mechanically evoked responses of the glutamatergic junction between hair cells and afferent neurons of the axolotl Ambystoma tigrinum. Pressure ejection of fraction D in concentrations ranging from 0.5 to 2 mg/ml (n = 9) decreased the spontaneous and mechanically evoked activity of semicircular canal afferent neurons and the responses evoked by kainic acid and alpha-amino-3-hydroxy-5-methylisoxasole-4-propionic acid. This action was also dose-dependent and partially reversible. These results indicate that fraction D acts as a glutamate receptor antagonist in snail and amphibian neurons. Further studies are required to characterize the active compounds responsible for this action and its specificity upon the subtypes of glutamate receptors.

Effects of a high molecular weight toxin from the sea anemone Condylactis gigantea on cholinergic responses.

1. The effects of a high molecular weight toxin isolated from the sea anemone Condylactis gigantea (Condytoxina 2) on the cholinergic responses were studied in two different preparations: identified cells of a land snail and enzymatically dissociated mice sensory neurons. These neurons were studied using intracellular recording and concentration clamp techniques respectively. 2. The toxin produces a concentration-dependent dual effect on the cholinergic responses in both preparations. Thus the application of the toxin at concentrations up to 25 nmol/l produces a reversible block of the response whereas higher doses potentiates it. 3. These results suggest that Condytoxina 2 contains an active compound(s) with the capacity to bind to the nicotinic acetylcholine receptor of excitable cells in both snail and mice neurons. During this action complex allosteric interactions among the binding sites could occur.

A computer program for the estimation of kinetic parameters of membrane currents based on the Gauss-Newton method.

A computer program based on the Gauss-Newton method was developed for the Hodgkin-Huxley estimation of kinetic parameters of membrane currents recorded in voltage-clamp experiments. Fast potassium current of land snail neurons was estimated, and found to be in agreement with literature reports.

Effects of a high molecular weight toxin from Physalia physalis on glutamate responses.

The effects of a high molecular weight toxin from Physalia physalis (P3) were investigated on glutamate evoked potentials in snail (Zachrysia guanesis) neurons and in crayfish (Cambarus clarkii) neuromuscular junction. The glutamate evoked potentials of snail neurons were reversibly blocked by P3 in a dose-dependent manner (2-200 microM). A reversible blocking action was also found for P3 on excitatory junctional potentials and on glutamate potentials of crayfish at a concentration range of 6 nM-60 microM. Experiments carried out with independent stimulation of the excitatory and inhibitory nerves showed that the effect of P3 (60 nM-10 microM) was exerted predominantly on excitatory junctional potentials. However, at higher doses (greater than 10 microM) a slight reduction of the inhibitory potentials was also observed. These results suggest that P3 reversibly blocks glutamate receptors. Thus, it could be a promising tool for further studies on glutamatergic transmission.