stretch receptors

Insects sense vibrations and body movements with chordotonal organs, specialized stretch receptors that monitor relative motion between body parts. We have performed a combination of electrophysiological and micromechanical experiments on living lch5 organs of Drosophila larvae. These chordotonal organs are pre-tensioned by accessory cap cells. We found that the extracellular matrix surrounding the cap cells maintains the basic resting tension. The extremely elastic cap cells contain microtubules, actin structures, and nonmuscle myosin-II motors. We found that myosin-II motor activity drives cap cell contraction and is involved in sensory adaptation. Optogenetic activation of myosin-II in the cap cells induced contractions and triggered spiking responses of the mechanoreceptors. Cap cell-specific knockdown of the regulatory light chain of myosin-II lowered tension in the chordotonal organs, decreasing the cap cell elastic modulus. Along with these mechanical effects, mechanoreceptor responses became more tonic, reflecting alterations in spiking synchronicity and mechanosensory adaptation.