China
Africa
Explore chapters and articles related to this topic
Neurotransmission at Parasympathetic Nerve Endings
Published in Kenneth J. Broadley, Autonomic Pharmacology, 2017
The nicotinic receptor has been extensively studied in skeletal muscle and the electric organ of the electric ray (Torpedo) and identified as a pentamer, the five units arranged symmetrically around an ion channel (see Figure 11.2). Purification of the receptor has led to the isolation of cDNAs that encode for these subunits and this has facilitated the cloning of genes of the receptor subunits from mammalian neurones and skeletal muscle. Differences between the NM and NN nicotinic receptors have therefore been confirmed by molecular biology, each being composed of different combinations of subunits (α, β, τ and δ) in their pentomer structure. These subunits consist of amino acid sequences probably arranged into a-helixes as four transmembrane domains. The α-subunits carry the recognition site for Ach and are pseudo-irreversibly bound by the α-toxin, α-bungarotoxin, from the venom of a snake, the Taiwan banded krait (Bungarus multicinctus). This toxin selectively inhibits neuromuscular (NM) nicotinic receptors. The α-subunits in skeletal muscle nicotinic receptors are α1 and two distinct types, α1a and α1b, have been cloned. Neuronal nicotinic receptor α-subunits are α2 but multiple subtypes (α2 to α8) have been cloned from chick and rat autonomic and central nervous systems. The neuronal nicotinic receptor is blocked by a minor component of the Bungarus venom, known as n-bungarotoxin and equivalent to K-bungarotoxin (Watson & Girdlestone 1994). The structure and function of the nicotinic neuronal receptor are described in more detail in Chapter 11.
Quantitative proteomic analysis of venom from Southern India common krait (Bungarus caeruleus) and identification of poorly immunogenic toxins by immune-profiling against commercial antivenom
Published in Expert Review of Proteomics, 2019
Aparup Patra, Abhishek Chanda, Ashis K. Mukherjee
Indian cobra (Naja spp) venom has been shown to contain only post-synaptic neurotoxins [18,30]; however, the occurrence of both pre- and post-synaptic neurotoxins has been reported in Bungarus venom [14,15]. This variation may explain the different pathophysiologies seen in krait and cobra envenomation [54]. The β-bungarotoxin and κ-bungarotoxin (a subtype of 3FTx) representing pre-synaptic neurotoxin and post synaptic neurotoxin, respectively are present in krait venom [14,15]. The proteomic analysis revealed that SI B. caeruleus venom is comprised of a substantial amount of β-bungarotoxin (12.9%) and κ-BTx (5.24%) (Figure 2, Table 1). The β-bungarotoxin causes triphasic effects at the terminus – inhibition initially, a small spike of ACh release, then further inhibition of release. By depleting the ACh vesicles, activation causes the degeneration of the motor nerve terminal [55,56]. The effect of β-bungarotoxins on sphincter pupillae, levator palpebral superioris, neck muscles, bulbar muscles, the limbs, and finally, the diaphragm that leads to respiratory failure, are the primary symptoms of krait envenomation [53]. The κ-BTx affects the neuronal-type of nicotinic cholinoceptors (AChR) at the post-synaptic level in central cholinergic synapses in autonomic ganglia [57]. Because the damage caused by the pre-synaptic neurotoxin is irreversible, the neurological manifestation lasts for 2–3 weeks, as is observed in krait-envenomed patients [53].