Electrical 'tuning' in muscle spindle receptors.

A variety of mechanical and electrical mechanisms have been shown to tune sensory receptors to selected stimuli. This study demonstrates the presence of electrical tuning in the mammalian muscle spindle. Apamin and tetraethyl ammonium ions (TEA), blockers of Ca2+-activated K+ channels, and ZnCl2, a Ca2+ channel blocker, were shown to change the dynamic behavior of the muscle spindle. We conclude that a Ca2+-activated K+ channel in the sensory nerve of the spindle provides negative feedback which alters its dynamic behavior tending to compensate for muscle dynamics. This mechanism is similar to that found in sensory hair cells in the cochlea and vestibule and may represent a general strategy for tuning in sensory receptors.