Tarantulas: Possible Lifesavers?

In the past, I have written about many creatures in the animal kingdom, and several of them were on the top of the most hated and feared list. Rats, spiders and snakes are prime examples.

My earlier article about spiders described how spider webs could be used to fashion artificial ligaments or tendons.¹ Tarantulas, another arachnid in that species, may prove valuable in treating a number of pathologies. This article will describe them, their venom, mechanisms of action and possible therapeutic use.

Description

The name "tarantula" is derived from the city of Taranto in Northern Italy, and a popular dance, the tarantella. It has been proposed real or imaged bites were used as an excuse to dance wildly, something the church frowned upon at that time.²

Tarantulas give some people the creeps because of their large, hairy bodies and legs. But these spiders are harmless to humans (except for a painful bite), quite docile, and their mild venom is weaker than a typical bee sting. It is most likely to cause a nasty local reaction including pain, redness and swelling.

Some people can have an allergic or anaphylactic reaction in the same way some people react to bee stings, and in these instances, reactions can be fatal. There also are a few species from Africa and Asia which have stronger venom that could potentially be fatal.

Tarantulas can use their legs to rub the barbed hairs from their abdomens and fling them in the direction of a threat. The hairs can cause a nasty, irritating rash.³

Other than sheer size, tarantulas are set apart from the rest of the spiders by having the following combination of characteristics:⁴

1. They breathe using two pairs of book lungs.
2. They have fangs that move up and down instead of sideways (like other spiders).
3. They have two claws and adhesive pads on each foot.

Tarantulas periodically shed their external skeletons in a process called molting. In the process, they also replace internal organs, such as female genitalia and stomach lining, and even regrow lost appendages.⁵

Tarantula blood is very different from the blood of vertebrates. It is called hemolymph, and is a clear, sometimes pale blue or yellow color.⁶

There are at least 800 different tarantula species found in most of the world's tropical, subtropical and arid regions. The largest tarantulas have an incredible leg span of nearly 10 inches. They can eat insects, small birds and reptiles, and even other spiders.

Some are easy to handle, whereas others are extremely aggressive.⁷ Tarantulas vary in color and behavior according to their specific environments. Generally, however, they are burrowers that live in the ground.⁸

A tarantula doesn't use a web to ensnare prey, though it may spin a trip wire to signal an alert when something approaches its burrow. These spiders grab with their appendages, inject paralyzing venom and dispatch their unfortunate victims with their fangs.

They also secrete digestive enzymes to liquefy their victims' bodies so that they can suck them up through their straw-like mouth openings. After a large meal, the tarantula may not need to eat for a month.⁹

Tarantulas have few natural enemies, but parasitic pepsis wasps are a formidable exception. Such a wasp will paralyze a tarantula with its sting and lay its eggs on the spider's body. When the eggs hatch, the wasp larvae gorge themselves on the still-living tarantula.¹⁰

The tarantula's own mating ritual begins when the male spins a web and deposits sperm on its surface. He copulates by using his pedipalps (short, leg-like appendages located near the mouth) and then scuttles away, if he's lucky. Females will sometimes eat their mates, if they can catch them.¹¹

Females seal both eggs and sperm in a cocoon and guard it for six to nine weeks, allowing 500 to 1,000 baby tarantulas to hatch. Females are also famous for their longevity. They can live up to 30 years in the wild, and have been known to live for over 20 years in captivity.¹² Males have a much shorter life span, only 5 to 10 years on average barring post-coital consumption.

Venoms

Tarantula venom is a combination of paralyzing agents and digestive enzymes. The paralyzing agent has been found to block a basic mechanism in cells important to a wide range of biological functions. This is no surprise considering that tarantulas have evolved their venoms over many millions of years, and they contain potent and selective toxins which target physiological processes in humans.¹³

The venom from the Chilean rose tarantula, for example, contains toxins with an anesthetic action. One study found some venoms include chemicals targeting the same pain pathways as chili peppers.¹⁴ These venoms activate the sensory nerves of their enemies just as certain plants do.

Mechanism of Action

There is a unique peptide found in the Chilean rose tarantula venom, labeled GsMTx4, that is the only agent known to block pores in cell membranes called mechanosensitive ion channels. According to one of the primary researchers, they are the transducers that turn mechanical stress into cellular signals.¹⁵

Mechanosensitive channels are proteins found in prokaryotic and eukaryotic cell membranes. They are believed to play roles in touch, hearing, cardiovascular regulation, sensing of gravity and osmotic stress.

Mechanotransducers are essential in regulating cell volume and division.¹⁶ The biochemistry, molecular biology and physiology are extremely complicated and beyond the scope of this article.

Here is an example: "It has been found that stretch activated ion channels (SAC) function as cardiac mechanotransducers. Mechanical stretch of intact tissue, isolated myocytes, or membrane patches rapidly elicit the opening of poorly selective cation, K+ and Cl- SAC. Several voltage and ligand-gated channels also are mechanosensitive. SAC alter cardiac electrical activity and, with prolonged stretch, cause an intracellular accumulation of Ca+2 and Na+ that can serve to trigger multiple signaling cascades and ultimately may contribute to remodeling of the heart in response to hemodynamic stress."¹⁷

It is more realistic to simply state there are mechanical forces impinging on the heart that play multiple roles in controlling cardiac function.^18,19 This information is of interest, however, to discern how the tarantula's peptide works in blocking the mechanical transduction in cells.

According to one researcher, stretch-activated channels are probably involved in many normal tissue functions that involve changes in mechanical stress, such as bladder filling, the heart and circulatory system, changes in blood pressure and fluid balance.²⁰

Possible Therapeutic Uses

Dr. Fred Sachs and his colleagues in the Center for Single Molecule Biophysics in the University of Buffalo's School of Medicine and Biomedical Sciences have isolated a peptide from tarantula venom that shows promise as a therapy for conditions as disparate as muscular dystrophy, neuropathic pain and cardiac arrhythmias.

Atrial fibrillation is the most common sustained cardiac arrhythmia that occurs in humans, secondary to valve disease, hypertension or heart failure. One report demonstrated atrial fibrillation potentiated by dilatation in the rabbit's heart can be inhibited by blocking stretch-activated channels with a specific peptide from tarantula venom.²¹

When the atria of the heart are stretched by overfilling, the heart starts to beat irregularly, or fibrillate, and may develop blood clots that can prove fatal. Laboratory studies indicate GsMtx-4 reversibly inhibits the irregular heartbeat without affecting the strength of contraction. This small 35 amino acid protein substance is found in the venom of the species, Grammostola spatulata, the Chilean rose tarantula mentioned above.

The peptide is being studied as therapy for muscular dystrophy, a condition one pharmaceutical company has been investigating for several years.²² Studies in mice indicate the peptide increases muscle strength without negative side effects, and the company is developing methods to deliver the drug.

There is another possible indication as a treatment for neuropathic pain. Research groups in Korea and at the University of California, San Francisco, have shown GsMtx-4 can inhibit mechanically induced pain originating in nerve fibers. Early results indicate the therapy is at least half as effective as morphine without acting on the brain.²³

As incredible as it seems, GsMtx-4 may also have other applications. It has shown the peptide stimulates neuronal growth, and it may be useful for treating Parkinson's disease.

Final Thoughts

After reading this article, readers may have a higher regard for tarantulas, less fear and perhaps even an eagerness to own one. Those so inclined should know that tarantulas are relatively easy to care for. They are calm in temperament, low maintenance and can be kept at room temperature.

Experts, however, advise against holding them. Despite their appearance, tarantulas are extremely fragile creatures, and best left alone.²⁴ Books describing their care are readily available from pet stores.

One other bit of information: there is no truth to the legend someone bitten by a tarantula must dance to an upbeat tempo (the tarantella) to sweat the poison out. A visit to the family physician or emergency room would likely have a better result.

References

1. Sherman M. "Spiders-Vile, But Valuable." Regulatory Focus. www.raps.org/focus-online/print-archives/article/162/may-2011-science-technology-spiders-vile-but-valuable.aspx. Accessed 3 August 2012.
2. Marshall S.: Tarantulas and Other Arachnids. Barrons Ed Series, Hauppauge, NY, 2001.
3. National Geographic. "Animals: Nat Geo Wild." animals.nationalgeographic.com/animals/. Accessed 3 August 2012.
4. Op cit 2.
5. Op cit 3.
6. Op cit 2.
7. Worsley School Online. "Tarantulas." www.worsleyschool.net/science/files/tarantula/tarantula.html. Accessed 3 August 2012.
8. Ibid.
9. Op cit 3.
10. About.com. "10 Cool Facts About Tarantulas." insects.about.com/od/spiders/a/10-facts-about-tarantulas.htm. Accessed 3 August 2012.
11. Op cit 7.
12. Op cit 10.
13. Ibid.
14. Owen J. "Tarantuala Venom, Chili Peppers Have Same 'Bite,' Study Finds." National Geographic. news.nationalgeographic.com/news/pf/77957034.html. Accessed 3 August 2012.
15. Baumgarten CM. "Origin of Mechanotransduction: Stretch-Activated Ion Channels. National Institute of Health. http://www.ncbi.nlm.nih.gov/books/NBK6374/?report=printable. Accessed 3 August 2012.
16. Ibid.
17. Franz MR. "Mechano-electrical feedback in ventricular myocardium." Cardiovascular Research. 1996;32:15-24.
18. Tavi P et al. "Cardiac mechanotransduction: From sensing to disease and treatment." Trends in Pharmacological Sciences. 2001: 22:254-60.
19. Kohl P, Ravens U. "Mechano-electrical feedback and cardiac arrhythmias." Progress in Biophysics and Molecular Biology. 2003; 821:266.
20. Phoenix Tarantula Rescue. "About." www.facebook.com/pages/Phoenix-Tarantula-Rescue/220823937933637?sk=info. Accessed 3 August 2012.
21. Bode F et al. "Tarantula peptide inhibits atrial fibrillation." Nature. 2001;409:35.
22. Futurity.org. "Potential MD treatment from tarantulas." www.futurity.org/health-medicine/potential-ms-treatment-from-tarantulas/print. Accessed 3 August 2012.
23. Op cit 20.
24. Jacobi M. "Choosing a Tarantula." Tarantulas.com. www.tarantulas.com/choosing.html. Accessed 3 August 2012.