Stretch-induced release of proctolin from the dendrites of a lobster sense organ.

Reversed-phase high-performance liquid chromatography coupled with a sensitive bioassay was used to quantify the content of proctolin in the peripheral sensory endings of a crustacean mechanoreceptor, the oval organ, and to examine for its release in response to the physiological stimulus of stretch. Material co-eluting with proctolin and showing proctolin-like bioactivity was present in the oval organ and in the nerve trunks containing the 3 sensory axons. Repetitive stretch stimulation, in which the dendrites were exposed to physiological stretch amplitudes, resulted in a significant increase in the release of proctolin from the oval organ in vitro. Approximately 11.7% of the total proctolin stored in the oval organ was released during a 5 min stimulation period. The stretch-evoked release of proctolin was calcium dependent. Since a previous study has shown that proctolin has excitatory effects upon these primary afferents, the present results imply that endogenous proctolin may function to self-modulate the sensory transduction mechanism of these sensory terminals.