Ion Channels Detects Heat

Biological Strategy

Common vampire bat

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Sense Temperature Cues From the Environment

Some living systems use their ability to perceive temperature to find prey or avoid predators, or as a way to gain information about their environment, such as whether they are near a warm or cold place. Temperature gradients can be subtle and modulate as they travel through water, air, or solids. Living organisms must therefore have a variety of thermal sensors appropriate to a given medium (liquid, gas, solid). Some even have a way to “visualize” a signal’s source. For example, the rattlesnake has heat sensors with thousands of nerve endings located in pit-shaped holes on each side of its face. The sensitivity of the pits overlaps, giving the snake a bifocal image of the heat’s source.

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Mammals

Class Mammalia (“breast”): Bats, cats, whales, horses, humans

Mammals make up less than 1% of all animals on earth, but they include some of the most well-known species. We know first-hand some of the characteristics that make mammals unique, like having hair, being able to sweat, and producing milk through mammary glands. Another critical shared feature is a set of highly-specialized teeth. Unlike sharks or alligators, for example, whose teeth are generally all the same size and shape, mammals have differently shaped teeth in different areas of the jaws to target specific foods or foraging strategies.

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'Pit organs' around the nose of vampire bat detects infrared radiation using ion channels.

“Histological studies of the bats’
facial structures indicate that thermal stimuli are most probably
perceived in the three pits surrounding the central nose leaf: the thin,
hairless and glandless skin is underlaid with dense connective tissue.
Thermography reveals that the surface temperature of the nasal region is
up to 9°C lower than that of the neighboring parts of the face (Fig.
2).” (Kürten and Schmidt 1982:223)

“Vampire bats (Desmodus rotundus) are obligate blood feeders that have evolved specialized systems to suit their sanguinary lifestyle.
Chief among such adaptations is the ability to detect infrared
radiation as a means of locating hotspots on warm-blooded prey. Among
vertebrates, only vampire bats, boas, pythons and pit vipers are capable
of detecting infrared radiation.
In each case, infrared signals are detected by trigeminal nerve fibres
that innervate specialized pit organs on the animal’s face.
Thus, vampire bats and snakes have taken thermosensation to the extreme
by developing specialized systems for detecting infrared radiation. As
such, these creatures provide a window into the molecular and genetic
mechanisms underlying evolutionary tuning of thermoreceptors in a
species-specific or cell-type-specific manner(…)Here we show that vampire bats tune a channel* that is already
heat-sensitive, TRPV1, by lowering its thermal activation threshold to
about 30 °C. This is
achieved through alternative splicing of TRPV1 transcripts to produce a
channel with a truncated carboxy-terminal cytoplasmic domain. These
splicing events occur exclusively in trigeminal ganglia, and not in
dorsal root ganglia, thereby maintaining a role for TRPV1 as a detector
of noxious heat in somatic afferents.” (Gracheva et al. 2011:88)

*Ion channels are pore-forming proteins that regulate the flow of ions across the membrane in all cells.

The channel acts like a little thermostat. “Altering its structure by leaving out part of the gene tunes the
ability of the channel to detect heat. By expressing different forms in
different tissues, the bats have split the function of the sensor,
maintaining its original function but also gaining the ability to
detect body heat for more efficient hunting.” (Wigmore 2011)

Last Updated August 18, 2016

References

Journal article

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