Role of the inhibitory effect of tetrodotoxin on the active sodium transport of the toad bladder

The enteric nervous system participates in the secretory response to the heat stable enterotoxins of Escherichia coli in rats and cats

Intestinal secretion was evoked in periarterially denervated jejunal segments of anesthetized rats and cats by exposing the intestines to the heat stable (ST) toxins from a strain of Escherichia coli producing both STa and STb toxins. The secretion was significantly inhibited and to about the same relative extent by the addition of each one of the three following drugs: hexamethonium (i.v., rats), lidocaine (applied on the serosal surface, rats) and tetrodotoxin (intra-arterial, cats). Atropine inhibited fluid secretion in some experiments. It is proposed that a nervous mechanism is mediating part of the secretory response to Escherichia coli heat stable toxins, since three different drugs, which influence nervous activity in different ways, significantly diminished the secretory response. A model for the secretory nervous reflex(es) within the enteric nervous system is proposed; Escherichia coli heat stable toxins activate a "receptor cell" in the epithelium, which then stimulates surrounding dendritic nerve endings via the release of unknown substance(s). A nicotinic receptor is involved but further characteristics of the nervous reflex(es) remain to be elucidated.

The involvement of intramural nerves in cholera toxin induced intestinal secretion

In previous reports we have suggested that nervous reflexes are involved in the pathophysiology of cholera secretion and that these nervous reflexes involve a cholinergic synapse and a neuron with vasoactive intestinal polypeptide (VIP) as neurotransmitter. These proposals were further analyzed in this study. Tetrodotoxin (TTX) and lidocaine applied on the serosal surface inhibited cholera secretion in segments of rat small intestine. Fluid absorption in control rats was not significantly changed. Hexamethonium given i.v. decreased cholera secretion in the cat. No additional inhibition of cholera secretion was observed after giving TTX close i.a. Furthermore, the intestinal secretion evoked by VIP was not influenced by hexamethonium given i.v. or TTX given close i.a. The present observations support the hypothesis of a role for nervous reflexes in cholera secretion. The results suggest that at least a major part of the proposed nervous reflex(es) in cholera have a cholinergic synapse. Furthermore, the VIP-ergic neuron is situated "distal" to the cholinergic neuron in the reflex(es) closer to the effector cells.

On the role of intramural nerves in the pathogenesis of cholera toxin-induced intestinal secretion

Intestinal secretion was produced in anesthetized cats and rats by exposing isolated intestinal segments to cholera enterotoxin. Giving, for example, tetrodotoxin, a nerve-conduction-blocking agent, or adding lidocaine, a local anesthetic agent, to the solution in the intestinal segments markedly inhibited the rate of choleraic secretion, and in most experiments a net absorption of fluid was observed. The results suggest that intramural nervous mechanisms are involved in the pathogenesis of choleraic secretion.

Partial characterization of a tetrodotoxin-binding component from nerve membrane

Tetrodotoxin from Japanese puffer fish has been labeled with tritium and purified from the crude mixture obtained. The interaction between the purified [(3)H]tetrodotoxin and membrane suspensions from the olfactory nerve of long-nosed garfish has been investigated by equilibrium dialysis. Tetrodotoxin binds to membrane suspensions with a dissociation constant K(D) = 8.3 nM. The nerve preparation binds 42 pmol of [(3)H]tetrodotoxin/g of wet tissue at saturating toxin concentrations. With various hydrolytic enzymes, the binding component is shown to be a protein embedded in a phospholipid environment. The binding is inhibited below pH 4.0 and is not stable towards heat. Tetrodotoxin binding is not inhibited by the local anesthetic, procaine.