Apamin
The small bee-venom neurotoxin that blocks SK potassium channels, why researchers use it, and what the animal studies do and do not show
Apamin is an 18-residue peptide from honeybee venom, about 2 to 3% of the venom's dry weight. It blocks small-conductance calcium-activated potassium (SK) channels at very low concentrations, which made it one of the standard tools of neuroscience and cardiac research for four decades. In mice and rats it has been tested against liver and kidney fibrosis, gout-like arthritis, a Parkinson's model and memory tasks. It is a toxin: injected into animals it causes tremor, convulsions and lung damage, and it has never been tested as a treatment in people.
No established human dose Details ↓
Recommended Dosing
No established human dose
Apamin has never been given to people as a treatment. In the human studies here it is a probe applied to tissue samples, muscle, brain and heart, to locate SK channels; every study that injected it used mice or rats, and the toxicity work shows convulsions, tremor and lung bleeding in animals.
What is it?
Apamin is one of several peptides in honeybee venom, alongside melittin and mast-cell degranulating peptide. It is small, 18 amino acids folded tightly by two disulfide bonds, and it was among the first toxins shown to act on a single class of potassium channel. A 1983 review described it as a neurotoxin specific to one family of calcium-dependent potassium channels, the family now called small-conductance calcium-activated potassium channels, or SK channels.
SK channels open when calcium rises inside a cell and let potassium out; they carry the slow after-hyperpolarisation that follows a nerve impulse and quiets the cell. Blocking them makes nerve and heart cells more excitable. Because apamin blocks them at picomolar to low nanomolar concentrations, researchers use it to ask what SK channels do in a tissue: a current that apamin removes is, by definition, an apamin-sensitive current. A 2010 study found apamin does not simply plug the pore but binds an outer site and changes the channel's shape, and a 2025 structure placed it at a narrow opening at the top of the pore. Its value as a tool rests on selectivity, and that has limits: one 2017 study found it also blocks the Kv1.3 potassium channel of immune cells, while a 2014 study found it spared the major sodium, calcium and potassium currents of the heart.
Measuring where apamin binds has been used to map SK channels in human tissue. Muscle from people with myotonic dystrophy carried apamin binding sites that normal muscle lacked, and hippocampus from people with Alzheimer's disease had fewer binding sites than controls. Failing human hearts showed a larger apamin-sensitive potassium current than hearts with normal pumping function. In each case apamin was the probe, applied to tissue in a dish, not a treatment.
In animals, injected apamin has been studied in several disease models. In mice it reduced scarring in models of liver fibrosis and biliary fibrosis, and in an animal model of a blocked ureter it reduced kidney fibrosis. It reduced paw swelling in a mouse model of gouty arthritis, and in a mouse model of multiple sclerosis the middle of three doses reduced T-cell entry into the brain. In a mouse Parkinson's model whole bee venom protected dopamine neurons and apamin alone did so only partly. Memory studies in the 1990s found improvements in some tasks in mice, but a broader study in mice and rats concluded apamin was a poor tool for this purpose because doses that helped mice also caused visible side effects.
The toxicity is the other half of the story. Small amounts injected into the brain of mice cause convulsions and breathing failure; injected into the body, apamin produced tremor, poor coordination and bleeding into the lungs of animals that died. None of the disease-model results has been tested in people, and none of them makes apamin a candidate for self-administration.
Mechanism of Action
Apamin binds the outer mouth of small-conductance calcium-activated potassium (SK) channels and stops them letting potassium out, so cells that rely on these channels to calm down after firing stay more excitable.
SK channel block
Binds an outer site of SK2 and SK3 channels, using an outer-pore histidine, and blocks current at very low concentrations (PMIDs 20562108, 41342453).
More excitable cells
Removing the SK current lengthens the electrical activity of heart cells, more so in failing hearts, and makes neurons fire more readily (PMID 23525437).
Off-target action
Also blocks the Kv1.3 potassium channel of immune cells, so effects in tissues carrying both channels cannot be pinned on SK alone (PMID 28108814).
Fibrosis signalling (animal and cell work)
In liver and kidney models it damped TGF-beta1, Smad and STAT3 signalling; how this links to SK channels is not settled (PMIDs 24878534, 34031696).
Published Research
These studies were read from their PubMed abstracts on October 29, 2026. They are channel studies, studies of human tissue using apamin as a probe, animal disease models, toxicity studies and reviews. None gave apamin to a person.
A toxin for one class of potassium channel
An early review established apamin as a neurotoxin that acts specifically on one class of calcium-dependent potassium channels, the basis for its later use as the defining blocker of SK channels.
What apamin does in disease models
A review of apamin's actions outside cancer. It puts apamin at about 2-3% of bee venom's dry weight, describes it as an 18-residue peptide held by two disulfide bonds that irreversibly blocks SK channels, and summarises cell and animal work on apoptosis, fibrosis and nervous-system disease.
How apamin blocks SK channels
Using patch clamp, binding studies, modelling and mutations, apamin bound SK2 and SK3 equally tightly but blocked SK3 current at much higher concentrations than SK2. An outer-pore histidine was needed for its action, and the results pointed to an allosteric block at an outer site rather than a plug deep in the pore.
A structure of apamin on the SK2 channel
Cryo-structures of an SK2-based channel showed apamin sitting at a narrow hydrophobic opening at the extracellular end of the pore, where it stops potassium ions leaving; small-molecule modulators bound elsewhere in the channel.
Not as selective as assumed
Apamin also blocked the Kv1.3 potassium channel with high affinity, about as potently as a dedicated Kv1.3 blocker. Because immune cells carry both SK and Kv1.3 channels, the authors warn that apamin must be used with care as a selective tool.
Spares the heart's other main currents
In cells expressing human cardiac channels and in rabbit heart cells, apamin did not change the main sodium, L-type calcium or major potassium currents, supporting its use to isolate the SK current in heart studies.
Larger SK current in failing human hearts
In heart cells from 12 failing hearts removed at transplant and from biopsies of hearts with normal pumping, the apamin-sensitive potassium current was about four times larger in heart failure, SK2 protein about three times higher, and blocking it lengthened the cells' electrical activity more in failing hearts.
Apamin binding sites in myotonic dystrophy muscle
Muscle membranes from patients with myotonic muscular dystrophy contained receptors for apamin, while normal human muscle and muscle from patients with spinal anterior horn disorders had none.
Fewer binding sites in Alzheimer's hippocampus
Autoradiography of brain tissue from 9 people with Alzheimer's disease and 8 controls found fewer labelled apamin binding sites in the subiculum and CA1 region in Alzheimer's disease; the loss tracked nerve-cell density, not plaque density.
Liver fibrosis in mice
In mouse liver cells, apamin blocked the scar-promoting changes triggered by TGF-beta1 and the signalling behind them, and in mice given carbon tetrachloride to scar the liver it prevented much of the tissue damage.
Biliary fibrosis in mice
In mice fed a diet that damages the bile ducts, apamin reduced liver injury, inflammatory signals, collagen build-up and bile-duct cell proliferation, and in a rat stellate-cell line it damped the cells' activation.
Kidney fibrosis after a blocked ureter
In a ureter-obstruction model of kidney scarring, apamin lowered markers of fibrosis and inflammation and reduced tubular injury, and in cultured kidney fibroblasts it blocked TGF-beta1 and STAT3 signalling.
Gouty arthritis in mice
In mice injected with urate crystals, both bee venom and apamin reduced paw swelling and inflammatory cytokines and inhibited the inflammasome; colchicine was the comparison treatment.
A mouse model of multiple sclerosis
In 30 mice with experimental autoimmune encephalomyelitis, the middle of three apamin doses lowered disease scores more than the highest dose and reduced CD8 T-cell entry into the brain over 14 days.
Partial protection in a Parkinson's model
In a chronic MPTP mouse model of Parkinson's disease, whole bee venom gave lasting protection to dopamine neurons; apamin alone reproduced that protection only in part, suggesting other venom components add to it.
Memory after training in mice
The authors note apamin binds the channels behind the slow after-hyperpolarisation that follows a nerve impulse. In mice it sped up learning of a lever-press task, partly by raising activity overall, and given just after training it improved memory; given later it had no effect.
A poor tool for memory research
Across water-maze, avoidance and operant tasks in mice and rats, evidence that apamin improves cognition was weak in rats and stronger in mice, but visible side effects appeared at doses close to those that helped, and the authors judged apamin a poor tool for studying SK channels in memory.
Toxicity: tremor and lung haemorrhage
Compared with another channel toxin, dendrotoxin, apamin injected into the brain caused tremor and ataxia without seizure activity; given into the body it caused similar signs and marked bleeding in the lungs of animals that died.
Neurotoxicity when injected into the brain
Injected into the brain ventricles of mice, apamin was about ten times more potent than a related bee-venom peptide at causing convulsions and respiratory arrest; injected into the rat spinal cord in nanogram amounts it caused local hyperexcitation lasting over a day.
No Established Human Dose
Apamin has never been given to people as a treatment. In the human studies here it is a probe applied to tissue samples, muscle, brain and heart, to locate SK channels; every study that injected it used mice or rats, and the toxicity work shows convulsions, tremor and lung bleeding in animals. There is no human dose to state, and an animal amount cannot be turned into one.
What this rests on: PMID 2419758, PMID 23525437, PMID 8560501, PMID 593441.
Educational information, not medical advice. The doses on this page come from approved labels, published studies and, where no study exists, amounts reported by users. None is a recommendation for you. An unapproved compound has no established safe or effective human dose, and products sold for “research use only” are not made or tested for people. Talk to a doctor before acting on anything on this site, including before you start, stop or change any medicine or dose. Full medical disclaimer.
What a Buyer Needs to Know
What is sold, how it is mixed, stored and taken, and what is known about its safety, quality and legal status. Each part names its source. Where we have none, it says unknown.
What is sold
Unknown: we hold no label and no published test that says what forms or vial sizes Apamin is sold in. A vial's own label is a seller's claim, not a source.
Mixing a vial: a worked example
Unknown: no human dose of Apamin has been established (see No Established Human Dose below), so there is no amount to work out. The reconstitution calculator does the arithmetic for any vial, water and dose.
Storage before and after mixing
Unknown: no label or published stability study on file says how to store Apamin, before or after mixing. The mixing guide sets out the general rules, with their sources: keep a mixed vial in the fridge, and use it promptly, as the bacteriostatic water label says of any drug dissolved in it. The 28 days often quoted is the limit for an opened multiple-dose vial from a manufacturer, an outer limit set for sterility, not a time a mixed solution has been shown to keep. Nobody has published how long Apamin stays intact once mixed.
How it is taken
Unknown: with no established human dose, there is no established way of taking Apamin. What the human studies gave and how is set out under No Established Human Dose.
What to expect, and when
Unknown: no cited half-life and no label or trial duration on this page says how long Apamin lasts or how long it was given. Results reported in the studies are under Published Research.
Side effects, and when to stop or get help
From the Side Effects section: Convulsions and respiratory arrest after injection into the brain of mice (PMID 593441); Tremor, poor coordination and bleeding into the lungs after injection into the body (PMID 8560501); Visible side effects in mice and rats at doses close to those tested for memory effects (PMID 10643819). Full list and cautions ↓
When to stop or get help: unknown; no label or trial on file sets rules for stopping Apamin. Treat a severe or unexpected reaction as a reason to stop and see a doctor.
Source: the Side Effects section below (“No person has been given apamin in a study read here”).
Interactions
Unknown: a PubMed search for human interaction studies of Apamin (reviewed 2026-10-28) found none. Unknown is not the same as safe to combine.
Every peptide's record, with its source: the interaction matrix.
Checking what you bought
Unknown: no published independent test of Apamin products is in our lab-results database yet, so how products sold under this name measure up is not known.
To read a certificate of analysis, paste it into the COA decoder; it checks the measured mass against Apamin's expected mass, 2,027.3 Da, from this entry's molecular data. Trust & Verification explains what independent testing can and cannot show.
Legal status
US: Research Chemical (Not a medicine: a venom toxin used in research). Sport: Prohibited (S0 catch-all).
Country by country ↓ · Regulatory tracker
Source: this entry's approval status and the WADA Prohibited List, as in Legal Status below.
Side Effects & Contraindications
Reported Side Effects
No person has been given apamin in a study read here. These effects come from animal studies.
Contraindications & Cautions
Apamin is a research toxin, not a medicine, so it has no labelled contraindications.
Legal Status
Apamin is a venom toxin used as a laboratory reagent. It is not a medicine anywhere.
Frequently Asked Questions
?What is apamin?
An 18-amino-acid peptide toxin from honeybee venom, folded by two disulfide bonds, that blocks small-conductance calcium-activated potassium (SK) channels.
?Is apamin a medicine?
No. It is a laboratory tool and a toxin. No study has given it to people as a treatment, and there is no approved product.
?Why do researchers use apamin?
Because it blocks SK channels at very low concentrations, a current that apamin removes is taken to be an SK current. That is how SK channels were mapped in heart, brain and muscle tissue.
?Is apamin perfectly selective?
Not quite. It spares the heart's main sodium, calcium and potassium currents, but one study found it also blocks the Kv1.3 potassium channel of immune cells.
?What did the animal studies find?
Reduced liver, bile-duct and kidney scarring, less inflammation in a gout model and a multiple sclerosis model, partial protection in a Parkinson's model, and mixed effects on memory. None has been tested in people.
?Is apamin dangerous?
Yes. In mice and rats it causes convulsions, tremor, breathing failure and bleeding into the lungs, and the doses that helped memory in one study were close to those causing side effects.
?Is apamin the same as bee venom therapy?
No. Bee venom is a mixture led by melittin; apamin is a small part of it. In a Parkinson's mouse model whole venom protected neurons more fully than apamin alone.
References
- [other] UniProt P01500: apamin, Apis mellifera; peptide residues 28 to 45, CNCKAPETALCARRCQQH, histidine amide, disulfides 28-38 and 30-42. Read October 28, 2026. https://www.uniprot.org/uniprotkb/P01500/entry
- [pubmed] Lazdunski M. "Apamin, a neurotoxin specific for one class of Ca2+-dependent K+ channels." Cell Calcium, 1983;4(5-6):421-8. PMID: 6323004.
- [pubmed] Gu H, et al. "Therapeutic Effects of Apamin as a Bee Venom Component for Non-Neoplastic Disease." Toxins (Basel), 2020;12(3). PMID: 32204567.
- [pubmed] Lamy C, et al. "Allosteric block of KCa2 channels by apamin." J Biol Chem, 2010;285(35):27067-27077. PMID: 20562108.
- [pubmed] Cassell SJ, et al. "Mechanism of SK2 channel gating and its modulation by the bee toxin apamin and small molecules." Elife, 2025;14. PMID: 41342453.
- [pubmed] Voos P, et al. "The small neurotoxin apamin blocks not only small conductance Ca(2+) activated K(+) channels (SK type) but also the voltage dependent Kv1.3 channel." Eur Biophys J, 2017;46(6):517-523. PMID: 28108814.
- [pubmed] Yu CC, et al. "Apamin does not inhibit human cardiac Na+ current, L-type Ca2+ current or other major K+ currents." PLoS One, 2014;9(5):e96691. PMID: 24798465.
- [pubmed] Chang PC, et al. "Heterogeneous upregulation of apamin-sensitive potassium currents in failing human ventricles." J Am Heart Assoc, 2013;2(1):e004713. PMID: 23525437.
- [pubmed] Renaud JF, et al. "Expression of apamin receptor in muscles of patients with myotonic muscular dystrophy." Nature, 1986;319(6055):678-80. PMID: 2419758.
- [pubmed] Ikeda M, et al. "Selective reduction of [125I]apamin binding sites in Alzheimer hippocampus: a quantitative autoradiographic study." Brain Res, 1991;567(1):51-6. PMID: 1667746.
- [pubmed] Lee WR, et al. "Apamin inhibits hepatic fibrosis through suppression of transforming growth factor β1-induced hepatocyte epithelial-mesenchymal transition." Biochem Biophys Res Commun, 2014;450(1):195-201. PMID: 24878534.
- [pubmed] Kim JY, et al. "Apamin suppresses biliary fibrosis and activation of hepatic stellate cells." Int J Mol Med, 2017;39(5):1188-1194. PMID: 28405682.
- [pubmed] Gwon MG, et al. "Apamin inhibits renal fibrosis via suppressing TGF-β1 and STAT3 signaling in vivo and in vitro." J Mol Med (Berl), 2021;99(9):1265-1277. PMID: 34031696.
- [pubmed] Lee YM, et al. "Apamin from bee venom suppresses inflammation in a murine model of gouty arthritis." J Ethnopharmacol, 2020;257:112860. PMID: 32289477.
- [pubmed] Fattahi H, et al. "Apamin as a BBB Shuttle and Its Effects on T Cell Population During the Experimental Autoimmune Encephalomyelitis-Induced Model of Multiple Sclerosis." Neurotox Res, 2021;39(6):1880-1891. PMID: 34487326.
- [pubmed] Alvarez-Fischer D, et al. "Bee venom and its component apamin as neuroprotective agents in a Parkinson disease mouse model." PLoS One, 2013;8(4):e61700. PMID: 23637888.
- [pubmed] Messier C, et al. "Effect of apamin, a toxin that inhibits Ca(2+)-dependent K+ channels, on learning and memory processes." Brain Res, 1991;551(1-2):322-6. PMID: 1913161.
- [pubmed] van der Staay FJ, et al. "Behavioral effects of apamin, a selective inhibitor of the SK(Ca)-channel, in mice and rats." Neurosci Biobehav Rev, 1999;23(8):1087-110. PMID: 10643819.
- [pubmed] Lallement G, et al. "Compared toxicity of the potassium channel blockers, apamin and dendrotoxin." Toxicology, 1995;104(1-3):47-52. PMID: 8560501.
- [pubmed] Habermann E. "Neurotoxicity of apamin and MCD peptide upon central application." Naunyn Schmiedebergs Arch Pharmacol, 1977;300(2):189-91. PMID: 593441.
Sources & Citations
Every study on this page was read from its PubMed record on October 29, 2026. The sequence is UniProt P01500's. Status comes from Drugs@FDA (openFDA) and the EMA medicines list, searched October 28, 2026. Grey Peptides sells nothing and links to no vendor.
Medical Disclaimer: This content is for educational and informational purposes only. It is not medical advice, and nothing here is an instruction to obtain or use any compound. Talk to a licensed clinician about your own situation.