Fly eyes have the fastest visual responses in the animal kingdom, but how they achieve this has long been an enigma. A new study shows that their rapid vision may be a result of their photoreceptors -- specialised cells found in the retina -- physically contracting in response to light. The mechanical force then generates electrical responses that are sent to the brain much faster than, for example, in our own eyes, where responses are generated using traditional chemical messengers...Research published in Science, as reported by Science Daily.
A fly's vision is so fast that it is capable of tracking movements up to five times faster than our own eyes. This performance is achieved using microvillar photoreceptor cells... As in all photoreceptors, phototransduction starts with absorption of light by a visual pigment molecule (rhodopsin). In microvillar photoreceptors this leads to activation of a specific enzyme known as phospholipase C... The key finding was that the photoreceptors physically contract in response to light flashes. The contractions were so small and fast that an "atomic force microscope" was needed to measure them. This revealed that the contractions were even faster than the cell's electrical response and appeared to be caused directly by PLC activity...
Professor Hardie said: "That a mechanical signal could be an intermediate signal -or 'second messenger'- in an otherwise purely biochemical cascade is a novel concept that extends our understanding of cellular signalling mechanisms to a new level."
Addendum: Reader Ben noted a similar observation of possible mechanical coupling in the brains of whitefly parasites, as described at New Scientist:
"...the neurons might not bother with conventional action potentials at all. "They could be sending signals mechanically," Laughlin says. The tiny axons might each carry a long rigid rod stretching down the centre. Pulling the rod could create a physical rather than electrical trigger for the release of a chemical that passes the signal on to the neighbouring neuron."More at the link. You learn something every day. Tx, Ben.