Extracellular or intracellular application of argiotoxin-636 has inhibitory actions on membrane excitability and voltage-activated currents in cultured rat sensory neurones

Synthesis and Biological Activities of Naturally Functionalized Polyamines: An Overview

Recently, extensive researches have emphasized the fact that polyamine conjugates are becoming important in all biological and medicinal fields. In this review, we will focus our attention on natural polyamines and highlight recent progress in both fundamental mechanism studies and interests in the development and application for the therapeutic use of polyamine derivatives.

Inhibition of neuronal tetrodotoxin-sensitive Na+ channels by two spider toxins: hainantoxin-III and hainantoxin-IV

Hainantoxin-III and hainantoxin-IV, isolated from the venom of the Chinese bird spider Seleconosmia hainana, are neurotoxic peptides composed of 33-35 residues with three disulfide bonds. Using whole-cell patch-clamp technique, we investigated their action on ionic channels of adult rat dorsal root ganglion neurons. It was found that the two toxins did not affect Ca2+ channels (both high voltage activated and low voltage activated types) nor tetrodotoxin-resistant voltage-gated Na+ channels (VGSCs). However, hainantoxin-III and hainantoxin-IV strongly depressed the amplitude of tetrodotoxin-sensitive Na+ currents with IC50 values of 1.1 and 44.6 nM, respectively. Both hainantoxin-III (1 nM) and hainantoxin-IV (50 nM) caused a hyperpolarizing shift of about 10 mV in the voltage midpoint of steady-state Na+ channel inactivation, but they showed difference in the reprime kinetics of VGSCs: hainantoxin-III significantly decreased the recovery rate from inactivation at a prepulse potential of -80 mV while hainantoxin-IV did not do. It is interesting to note that similar to huwentoxin-IV, the two hainantoxins did not affect the activation and inactivation kinetics of Na+ currents and at a concentration of 1 microM they completely inhibited the slowing inactivation currents induced by BMK-I (toxin I from the scorpion Buthus martensi Karsch), a scorpion alpha-like toxin. The results indicate that hainantoxin-III and hainantoxin-IV are novel spider toxins and affect the mammal neural Na+ channels through a mechanism quite different from other spider toxins targeting the neural receptor site 3, such as delta-aractoxins and mu-agatoxins.

Pharmacology and biochemistry of spider venoms

Spider venoms represent an incredible source of biologically active substances which selectively target a variety of vital physiological functions in both insects and mammals. Many toxins isolated from spider venoms have been invaluable in helping to determine the role and diversity of neuronal ion channels and the process of exocytosis. In addition, there is enormous potential for the use of insect specific toxins from animal sources in agriculture. For these reasons, the past 15-20 years has seen a dramatic increase in studies on the venoms of many animals, particularly scorpions and spiders. This review covers the pharmacological and biochemical activities of spider venoms and the nature of the active components. In particular, it focuses on the wide variety of ion channel toxins, novel non-neurotoxic peptide toxins, enzymes and low molecular weight compounds that have been isolated. It also discusses the intraspecific sex differences in given species of spiders.

Extracellular and intracellular actions of azadirachtin on the electrophysiological properties of cultured rat DRG neurones

The distinct electrophysiological actions of extracellular and intracellular azadirachtin (type A) were investigated using cultured dorsal root ganglion neurones from neonatal rats and the whole cell variant of the patch clamp technique. The cultured mammalian neurones were relatively insensitive to azadirachtin compared with some invertebrate preparations, such as insect chemosensory systems. Insect preparations have been found to respond to 1-100 nM azadirachtin. However, at concentrations of azadirachtin between 10 and 100 microM significant changes in the electrophysiological properties of cultured DRG neurones were seen. Extracellular application of azadirachtin prolonged the late repolarization phase of evoked action potentials and consistent with this produced modulation of voltage-activated K+ currents. This modulation involved an initial transient increase in K+ current followed by reversible inhibition when azadirachtin was applied at a concentration of 10 microM. Higher concentrations of azadirachtin (50 and 100 microM), had only inhibitory effects on voltage-activated K+ currents. Azadirachtin produced a degree of voltage-dependent inhibition, with a greater level of K+ current inhibition observed when neurones were held at -90 mV compared with -40 mV. Prolonged application of azadirachtin for 24 h reversibly reduced action potential amplitude. In contrast intracellular application of 100 microM azadirachtin via the patch pipette solution had no significant effects on action potentials but produced an increase in conductance. Intracellular azadirachtin activated several conductances including a TEA-sensitive K + current and an inward current that had an estimated reversal potential close to 0 mV. In conclusion, data showed that azadirachtin had different effects when it was applied inside and outside the neurones and that azadirachtin at high concentrations reversibly altered neuronal excitability mainly by modulating potassium conductances. It appears that rat cultured DRG neurones are less affected by azadirachtin than some insect sensory systems.