Iberiotoxin

Iberiotoxin is an ion channel toxin purified from the Eastern Indian red scorpion "Buthus tamulus".Iberiotoxin selectively inhibits the current through large-conductance calcium-activated potassium channels.

Chemistry

Iberiotoxin is a 37-amino acid peptide. [Ferrat G, Bernard C, Fremont V, Mullmann TJ, Giangiacomo KM, Darbon H. "Structural basis for alpha-K toxin specificity for K+ channels revealed through the solution 1H NMR structures of two noxiustoxin-iberiotoxin chimeras." "Biochemistry". 2001 Sep 18;40(37):10998-1006. PMID 11551195] It is also known as "Potassium channel toxin alpha-KTx 1.3" or IbTx. The complete amino acid sequence has been defined and it displays 68% sequence homology with charybdotoxin.Galvez A, Gimenez-Gallego G, Reuben JP, Roy-Contancin L, Feigenbaum P. Purification and characterization of a unique, potent, peptidyl probe for the high conductance calcium-activated potassium channel from venom of the scorpion "Buthus tamulus". J Biol Chem. 1990 Jul 5;265(19):11083-90. PMID 1694175]

Target and mode of action

Iberiotoxin binds to the the outer face of the large-conductance calcium-activated potassium channels (maxiK or BK channels) with high affinity (Kd ~1 nM).Candia S., Garcia ML, Latorre R. "Mode of action of iberiotoxin, a potent blocker of the large conductance Ca2+-activated K+ channel." "Biophysical Journal". 1992 Aug (63):583-590. PMID 1384740] It selectively inhibits the current by decreasing both the probability of opening and the open time of the channel.

Toxicity

The venom produces mainly cardiopulmonary abnormalities like circulatory derangements, myocarditis and changes in cardiac sarcolemmal ATPase and by these abnormalities it can finally cause death. In rural India the scorpion and its venom is a commonly known factor of children's death. The venom initially causes transient cholinergic stimulation (vomiting, profuse sweating, bradycardia, priapism, hypersalivation, and hypotension) which is followed by sustained adrenergic hyperactivity (hypertension, tachycardia, and myocardial failure). The adrenergic phase but not the cholinergic phase is a dose-dependent phenomenon.Bawaskar HS, Bawaskar PH. "Management of the cardiovascular manifestations of poisoning by the Indian red scorpion (Mesobuthus tamulus)." "British Heart Journal". 1992 Nov 68(11): 478–480. PMID 1467032]

Treatment

Treatment is mainly symptomatic. Local pain is treated by injecting dehydroemetine at the site of the sting. Hypovolaemia is corrected by oral rehydration solution. Agitated, confused and non-cooperative patients are given a 5% dextrose saline drip. Patients with hypertension on admission are given a single dose of 5 mg sublingual nifedipine and oral prazosin. The blood pressure in patients with hypertension is controlled with sublingual nifedipine alone. Patients with pulmonary oedema are propped up and given intravenous aminophylline, sodium bicarbonate, oral prazosin, and oxygen by mask.

References