Sodium channels steroids

Frog poison. Batrachotoxin (BTX) is a steroidal alkaloid from the skin of Phyllobates terribilis, a poisonous Colombian frog (source of the poison used on blowgun darts). In the presence of BTX, sodium channels in an excised patch stay persistently open when the membrane is depolarized. They close when the membrane is repolarized. Which transition is blocked by BTX ... 

The most famous of the many alkaloids isolated so far is without any doubt batrachotoxin and its derivatives. Batrachotoxin has a LD50 of 2 ug per kg body weight (mouse, i.m.), thus being the most toxic nonprotein substance at all. Because of its special pharmacologic activity to keep open irreversably the sodium channels of nerve cells it has become an important tool in the studies of sodium channels. Chemically the batrachotoxins are esters of a 20-hydroxy steroid, batrachotoxinin A, with different pyrrol carboxylic acids. Although the activities of the different batrachotoxins is qualitatively the same, it differs quantitatively according to the acid part of the molecule (refs. 14, 15). 

Fig. 1.16 Steroid-eluting electrode. Le/l Cross sectional diagram demonstrating the silicone rubber plug impregnated with dexamethasone sodium phosphate lying immediately behind the porous electrode and connected to it by a channel. Right Tined lead with a platinized platinum porous, steroid-eluting electrode. (Permission for use Medtronic.)...

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