Chemoreceptor-mediated elongation of stereocilium bundles tunes vibration-sensitive mechanoreceptors on cnidocyte-supporting cell complexes to lower frequencies

Abstract

ABSTRACT Cnidocyte-supporting cell complexes (CSCCs) discharge nematocysts into targets upon coincidental stimulation of specific chemoreceptors and contactsensitive mechanoreceptors. In addition, CSCCs in the tentacles of at least one species of sea anemone discharge nematocysts into targets vibrating at specific frequencies. In seawater alone, these CSCCs discharge nematocysts preferentially at 55, 50 and 75 Hz. In the presence of 10−7M N-acetylneuraminic acid (NANA) or mucin, the CSCCs discharge nematocysts preferentially at the lower frequencies of 0, 5, 15, 30 and 40 Hz. Furthermore, the stereocilium bundles (SBs) within ciliary cones of CSCCs elongate significantly from a mean length of 6.08 /on in seawater to 7.14 μm in 10−7M mucin. The responses of (1) shifting the optimal frequencies for discharging nematocysts to lower frequencies and (2) elongating the SBs both exhibit dose-dependency and temporal adaptation to chemosensitizer. We conclude that these responses are controlled by CSCC chemoreceptors for N-acetylated sugars. We suggest that specific size-classes of SBs respond to specific frequencies of vibration, since the dose-response parameters to NANA depicting the relative abundances of SB size classes measuring 3–4, 5 and 7 μm correlate with dose-response parameters for the discharge of nematocysts into targets vibrating at 75, 55, and 30 Hz. Treating tentacles with cytochalasin disorganizes the SBs of ciliary cones and decreases the number of frequency optima for nematocyst discharge without significantly affecting nematocyst discharge into static targets. Thus, ciliary cones on CSCCs are vibration-sensitive mechanoreceptors that can be tuned by chemoreceptors to specific, lower frequencies by the elongation of SBs.