Microtubules and Microfilaments Participate in the Inhibition of Synaptosomal Noradrenaline Release by Tetanus Toxin

Abstract

Tetanus toxin (TeTX) has been demonstrated to inhibit transmitter release by two mechanisms: Zn 2~-dependent proteolytic cleavage of synaptobrevin and activation of a neuronal transglutaminase. Herein, attenuation of TeTX-induced blockade of noradrenaline release from synaptosomes was achieved by prior disassembly of microfilaments with cytochalasin D or breakdown of microtubules by colchicine or nocodazole. These drugs and monodansylcadaverine, a transglutaminase inhibitor, displayed some additivity in antagonizing the inhibitory effect of the toxin on synaptosomal transmitter release; as none of them reduced synaptobrevin cleavage, all appear to work independently of the toxin's proteolytic action. Prior stabilization of microtubules with taxol prevented the antagonism seen with coichicine, highlighting that this cytoskeletal component is the locus of the effect of coichicine. Replacement of Ca2~with Ba2~caused disappearance of the fraction of evoked secretion whose inhibition by TeTX is reliant on polymerized actin but did not alter the blockade by toxin that is dependent on microtubules. Two temporally distinguished phases of release were reduced by TeTX, and colchicine lessened its effects on both. Blockade of the fast phase ( 10 s) of secretion by TeTX was unaffected by cytochalasin D, but it clearly antagonized the toxin-induced inhibition of the slow (10-s to 5-min) component; it is notable that such antagonism was accentuated during a second bout of evoked release. These findings are consistent with sustained release requiring dissociation of synaptic vesicles from the microfilaments, a step that seems to be perturbed by TeTX.

Release of dopamine from human neocortex nerve terminals evoked by different stimuli involving extra‐ and intraterminal calcium

“…In all previous work with rat striatal synaptosomes incubated with TeTx for 90 min, the K + ‐evoked overflow of DA could maximally be inhibited by only 40% (Fassio et al ., 1999). The release of other transmitters from rat synaptosomes depolarized with high‐K + also was only in part sensitive to clostridial toxin incubation (Habermann et al ., 1988; McMahon et al ., 1992; Ashton & Dolly, 1997). The reasons for the apparent higher sensitivity to TeTx of DA exocytosis from human mesocortical endings are at present unclear.…”

A tetanus toxin sensitive protein other than VAMP 2 is required for exocytosis in the pancreatic acinar cell

“…All three neurotoxins (100 nM) cleaved the entire pool cellubrevin present in the permeabilized acini indicating that cellubrevin, like VAMP 2, does not appear to be required for exocytosis in the acinar cell. It has been suggested that TeTx inhibits neurotransmitter release by stimulation of transglutaminase [27,28]. Although there is no evidence that transglutaminase has any significant influence on exocytosis in exocrine cells, this study does highlight the possibility that TeTx inhibits exocytosis in the acinar cell by influencing a protein other than a VAMP isoform.…”

Bacterial Toxins and the Nervous System: Neurotoxins and Multipotential Toxins Interacting with Neuronal Cells

“…Possibly, TeNT stimulation of TGase II leads to reduced synaptic vesicle availability for release. This view is supported by several observations: (i) the depolarization-stimulated phosphorylation and redistribution of synapsin-I is altered after the action of TeNT [239]; (ii)the blocking action of TeNT is diminished after disassembly of microfilaments [150] and (iii)the amplitude of post-tetanic potentiation, a plasticity paradigm which involves synapsin-I in Aplysia synapses, is highly reduced after TeNT treatment [36,237]. As TeNT can access VAMP-2 only during a defined “physiological window” [41,44], TGase-II activation may modulate this access via the modification of proteins involved in regulation of the synaptic vesicle cycle ( i.e.…”