Iberiotoxin (IbTX) is an

ion channel Ion channels are pore-forming membrane proteins that allow ions to pass through the channel pore. Their functions include establishing a resting membrane potential, shaping action potentials and other electrical signals by gating the flow of io ...

toxin A toxin is a naturally occurring organic poison produced by metabolic activities of living cells or organisms. Toxins occur especially as a protein or conjugated protein. The term toxin was first used by organic chemist Ludwig Brieger (1849– ...

purified from the Eastern Indian red

scorpion Scorpions are predatory arachnids of the order Scorpiones. They have eight legs, and are easily recognized by a pair of grasping pincers and a narrow, segmented tail, often carried in a characteristic forward curve over the back and always end ...

Hottentotta tamulus ''Hottentotta tamulus'', the Indian red scorpion, also known as the eastern Indian scorpion, is a species of scorpion of the family Buthidae. It occurs in most of India, eastern Pakistan and the eastern lowlands of Nepal, and recently from Sri L ...

''. Iberiotoxin selectively inhibits the

current Currents, Current or The Current may refer to: Science and technology * Current (fluid), the flow of a liquid or a gas ** Air current, a flow of air ** Ocean current, a current in the ocean *** Rip current, a kind of water current ** Current (stre ...

through large-conductance

calcium-activated potassium channel Calcium-activated potassium channels are potassium channels gated by calcium, or that are structurally or phylogenetically related to calcium gated channels. They were first discovered in 1958 by Gardos who saw that calcium levels inside of a cell ...

Chemistry

Iberiotoxin is a 37-

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

peptide Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides. A ...

. The formula is C₁₇₉H₂₇₄N₅₀O₅₅S₇. It is also known as "Potassium channel toxin alpha-KTx 1.3" or IbTx. The complete

sequence has been defined and it displays 68%

sequence homology Sequence homology is the biological homology between DNA, RNA, or protein sequences, defined in terms of shared ancestry in the evolutionary history of life. Two segments of DNA can have shared ancestry because of three phenomena: either a spe ...

with

charybdotoxin Charybdotoxin (CTX) is a 37 amino acid neurotoxin from the venom of the scorpion '' Leiurus quinquestriatus hebraeus'' (''deathstalker'') that blocks calcium-activated potassium channels. This blockade causes hyperexcitability of the nervous syst ...

Target and mode of action

Iberiotoxin binds to the outer face of the large-conductance calcium-activated potassium channels (maxiK or

BK channel BK channels (big potassium), are large conductance calcium-activated potassium channels, also known as Maxi-K, slo1, or Kca1.1. BK channels are voltage-gated potassium channels that conduct large amounts of potassium ions (K+) across the ce ...

s) with high affinity (Kd ~1 nM). 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 Myocarditis, also known as inflammatory cardiomyopathy, is an acquired cardiomyopathy due to inflammation of the heart muscle. Symptoms can include shortness of breath, chest pain, decreased ability to exercise, and an irregular heartbeat. The ...

and changes in cardiac

sarcolemma The sarcolemma (''sarco'' (from ''sarx'') from Greek; flesh, and ''lemma'' from Greek; sheath) also called the myolemma, is the cell membrane surrounding a skeletal muscle fiber or a cardiomyocyte. It consists of a lipid bilayer and a thin oute ...

ATPase ATPases (, Adenosine 5'-TriPhosphatase, adenylpyrophosphatase, ATP monophosphatase, triphosphatase, SV40 T-antigen, ATP hydrolase, complex V (mitochondrial electron transport), (Ca2+ + Mg2+)-ATPase, HCO3−-ATPase, adenosine triphosphatase) are ...

and by these abnormalities it can finally cause death. In rural

India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...

the scorpion and its venom is a commonly known factor of children's death. The venom initially causes transient

cholinergic Cholinergic agents are compounds which mimic the action of acetylcholine and/or butyrylcholine. In general, the word "choline" describes the various quaternary ammonium salts containing the ''N'',''N'',''N''-trimethylethanolammonium cation. F ...

stimulation (vomiting, profuse sweating,

bradycardia Bradycardia (also sinus bradycardia) is a slow resting heart rate, commonly under 60 beats per minute (BPM) as determined by an electrocardiogram. It is considered to be a normal heart rate during sleep, in young and healthy or elderly adults, a ...

priapism Priapism is a condition in which a penis remains erect for hours in the absence of stimulation or after stimulation has ended. There are three types: ischemic (low-flow), nonischemic (high-flow), and recurrent ischemic (intermittent). Most cases ...

hypersalivation Hypersalivation, or ptyalism, also known as sialorrhea or hypersialosis is the excessive production of saliva. It has also been defined as increased amount of saliva in the mouth, which may also be caused by decreased clearance of saliva.Medscape ...

, and

hypotension Hypotension is low blood pressure. Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood. Blood pressure is indicated by two numbers, the systolic blood pressure (the top number) and the dias ...

) which is followed by sustained

adrenergic Adrenergic means "working on adrenaline (epinephrine) or noradrenaline (norepinephrine)" (or on their receptors). When not further qualified, it is usually used in the sense of enhancing or mimicking the effects of epinephrine and norepinephrine ...

hyperactivity (

hypertension Hypertension (HTN or HT), also known as high blood pressure (HBP), is a long-term medical condition in which the blood pressure in the arteries is persistently elevated. High blood pressure usually does not cause symptoms. Long-term high bl ...

tachycardia Tachycardia, also called tachyarrhythmia, is a heart rate that exceeds the normal resting rate. In general, a resting heart rate over 100 beats per minute is accepted as tachycardia in adults. Heart rates above the resting rate may be normal (su ...

, and myocardial failure). The adrenergic phase but not the cholinergic phase is a dose-dependent phenomenon.{{cite journal , last1 = Bawaskar , first1 = HS , last2 = Bawaskar , first2 = PH , title = Management of the cardiovascular manifestations of poisoning by the Indian red scorpion (Hottentotta tamulus) , journal = British Heart Journal , volume = 68 , issue = 5 , pages = 478–80 , year = 1992 , pmid = 1467032 , pmc = 1025191 , doi=10.1136/hrt.68.11.478

Treatment

Treatment is mainly symptomatic. Local

pain Pain is a distressing feeling often caused by intense or damaging stimuli. The International Association for the Study of Pain defines pain as "an unpleasant sensory and emotional experience associated with, or resembling that associated with, ...

is treated by injecting

dehydroemetine Dehydroemetine is a synthetically produced antiprotozoal agent similar to emetine in its anti-amoebic properties and structure (they differ only in a double bond next to the ethyl substituent), but it produces fewer side effects. In the United S ...

at the site of the sting.

Hypovolaemia Hypovolemia, also known as volume depletion or volume contraction, is a state of abnormally low extracellular fluid in the body. This may be due to either a loss of both salt and water or a decrease in blood volume. Hypovolemia refers to the los ...

is corrected by oral rehydration solution. Agitated, confused and non-cooperative patients are given a 5% dextrose saline drip. Patients with

on admission are given a single dose of 5 mg sublingual

nifedipine Nifedipine (3,5-dimethyl 2,6-dimethyl-4-(2-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylate), sold under the brand name Adalat and Procardia, among others, is a calcium channel blocker medication used to manage angina, high blood pressure, Ra ...

and oral

prazosin Prazosin is an α1 blocker medication primarily used to treat high blood pressure, symptoms of an enlarged prostate, and nightmares related to post-traumatic stress disorder (PTSD). It is a less preferred treatment of high blood pressure. Oth ...

. The blood pressure in patients with hypertension is controlled with sublingual nifedipine alone. Patients with pulmonary

oedema Edema, also spelled oedema, and also known as fluid retention, dropsy, hydropsy and swelling, is the build-up of fluid in the body's tissue. Most commonly, the legs or arms are affected. Symptoms may include skin which feels tight, the area ma ...

are propped up and given intravenous aminophylline,

intravenous sodium bicarbonate Intravenous sodium bicarbonate, also known as sodium hydrogen carbonate, is a medication primarily used to treat severe metabolic acidosis. For this purpose it is generally only used when the pH is less than 7.1 and when the underlying cause i ...

, oral

, and

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

by mask.

References

Ion channel toxins Poisons