Antagonistic Frequency Tuning of Hair Bundles by Different Chemoreceptors Regulates Nematocyst Discharge

Sea anemones capture prey by discharging nematocysts into them. Chemical and mechanical cues identify suitable prey to sensory receptor systems on the anemone. Conjugated N-acetylated sugars from prey bind to chemoreceptors on cnidocyte/supporting cell complexes to tune hair bundles on the complexes to lower frequencies matching prey movements. The hair bundles regulate discharge of microbasic p-mastigophore nematocysts into vibrating targets. Provided that proline receptors are activated after those for N-acetylated sugars, nematocyst discharge is tuned to much higher frequencies. Thus, anemone hair bundles are tuned to either higher or lower frequencies by antagonistic chemoreceptors. Chemoreceptors for proline can adapt to 10(-8) mol l-1 proline and yet respond to increases in proline concentration of less than 10(-15) mol l-1. Under these conditions, too few molecules of proline are added to activate chemoreceptors on all responding cnidocyte/supporting cell complexes. Evidence indicates that the extreme sensitivity of anemones to proline may be attributed, in part, to intercellular communication.