Question

due Wed Dec 6 at 5pm

2. In the presence of batrachotoxin, a steroidal alkaloid from the skin of a poisonous frog Na channels stay persistently open when the membrane is depolarized. They close when the membrane is repolarized. Which transition is blocked by BTX? Suggest a biochemical explanation for the effect.

Answer 1

Batrachotoxin (BTX) is a potent neurotoxin found in the skin of various poisonous frogs, it is a steroidal alkaloid with a tertiary amine, BTX specifically targets voltage-gated Na+ channels and, when bound it drastically modifies Na+ channel properties. Following four responses has been observed.

1. BTX shifts the activation gating to the hyperpolarizing direction by 30 to 50 mV. As a result, voltage-gated Na+ channels open readily even at resting membrane potentials.
2. BTX eliminates both fast and slow inactivation gating. Consequently, single BTX-modified Na+ channels remain open for hours, as recorded in planar lipid bilayers.
3. BTX reduces the single channel conductance by approximately 50%.
4. BTX alters the ion selectivity of Na+ channels.

How BTX causes all these changes at the same time is still not well understood.