Mechanosensitive ion channels of spiders: mechanical coupling, electrophysiology, and synaptic modulation

Arthropods have provided several important mechanoreceptor models because of the relatively large size and accessibility of their primary sensory neurons. Three types of spider receptors- tactile hairs, trichobothria, and slit sensilla-have given important information about the coupling of external mechanical stimuli to the neuronal membrane, transduction of mechanical force into receptor current, encoding of afferent action potentials, and efferent modulation of peripheral sensory receptors. Slit sensilla, found only in spiders, are particularly important because they allow intracellular recording from sensory neurons during mechanical stimulation. Experiments on slit sensilla have shown that their mechanosensitive ion channels are sodium selective, blocked by amiloride, and open more at low pH. This evidence suggests that the channels are members of the same molecular family as degenerins, acid-sensitive ion channels, and epithelial sodium channels. Slit sensilla have also yielded evidence about the location, density, single-channel conductance, and dynamic properties of the mechanosensitive channels. Spider mechanoreceptors are modulated in the periphery by efferent neurons and possibly by circulating chemicals. Mechanisms of modulation, intracellular signaling, and role of intracellular calcium are areas of active investigation.