Sensitivity and adaptation of ampullar receptors to rapid perilymphatic potassium changes

Abstract

1. Ampullar receptors are extremely sensitive to rapid K+-changes in the fluid bathing the basal pole. Small variation in perilympathic K+ (±0.5 mmol/l compared to normal perilymph K+ level of 2.5 mmol/l) are sufficient to facilitate the receptor resting discharge if K+ is increased, or produce inhibition if K+ is decreased. Extracellular and intracellular recordings from the ampullar nerve afferent fibres show that the effects of perilymphatic K+-changes result from a modified transmitter release from the synaptic pole of the hair cells. 2. The effects of external K+ change on postsynaptic activation of primary afferent axons and spike discharge are transient since ampullar receptors recover to the resting activity level within a few minutes. These effects occur even if the sensory organ is permanently maintained in a K+-modified perilymph.