Nonspecific cation channels

Black Widow spider venom contains several different protein fractions. The most significant component of the venom is the neurotoxin, a-latrotoxin. This neurotoxin acts at the presynaptic membrane of the neuronal and the neuromuscular junctions. The binding of the a-latrotoxin results in the opening of nonspecific cation channels, a massive influx of calcium, release of acetylcholine and norepinephrine and decreased uptake of the neurotransmitter. The neurotransmitter release is most likely responsible for hypertension, muscle fasciculations, and spasms frequently experienced by victims of a bite. Later, generalized muscle weakness and labored breathing may develop in severe cases. While the venom of the black widow spider has been characterized as being more potent than that of many poisonous snakes, the small amount of venom injected limits the degree of toxicity. 

A. Latrodectus (black widow) spider venom contains alpha-latrotoxin, which causes opening of nonspecific cation channels, leading to an increased influx of calcium and indiscriminate release of acetylcholine (at the motor endplate) and norepinephrine. 

The tributyltin benzoates were toxic to the K562 cellsJ Tributyltin benzoate (TBSB)-treated R562 cells showed a greater initial extracellular calcimn ion influx compared with the tributyltin halobenzoates. This is consistent with an early activation of endonucleases and DNA fragmentation in the TBSB-treated cells. This is also consistent with an earlier report by Chow et al. where the cytosolic-free calcimn ion concentration increases because of an extracellular calcium ion influx, an inhibition of the calcimn ion extrusion system, and the release of calcium from the intracellular reserves. These, and other studies, suggest involvement of nonspecific cation channels in the extracellular calcium ion influx that leads to an increase in observed cell viability. When the calcium channels were blocked with either verapamil or nefidipine, the extracellular calcium ion influx was partly inhibited and apotosis observed. 

Proteins that form ion-transporting channels are quite common among eukaryotes. The majority of these channels transport positive ions, such as Na, and Ca. However, CP channels have been recently observed. The cation channels function in a selective, nonspecific manner. For example, a channel may transport Na ions more efficiently than ions but both cations move through the channel. 

To accommodate the rapid diffusion that is often needed to supply food, water, and inorganic ions to cells, membranes contain a variety of small pores and channels. The pores may be nonspecific or they may be selective for anions or cations or for some other chemical characteristics. They may be permanently open or sometimes closed and referred to as gated. 

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