HAIR BUNDLES OF SEA-ANEMONES AS A MODEL SYSTEM FOR VERTEBRATE HAIR BUNDLES

Sea anemones are marine invertebrates that use hair bundles to detect swimming movements of prey. Prey are captured by nematocysts (stinging capsules) that discharge into the prey. To further characterize anemo ne hair bundles and to compare hair bundles in anemones with hair bund les in vertebrates, we investigated fine structure and cytochemistry o f anemone hair bundles. In addition, using a biological assay based on counting nematocysts discharged into vibrating test probes, we examin ed sensitivity of vibration detection to aminoglycoside antibiotics, C a2+-free seawater, and amiloride. Like vertebrate hair bundles, anemon e hair bundles are composed of stereocilia, possess lateral linkages b etween stereocilia whose preservation for transmission electron micros copy is enhanced by ruthenium red, and possess tip links morphological ly similar to vertebrate tip links. Furthermore, vibration-dependent d ischarge of nematocysts is reversibly inhibited by 10(-4) M streptomyc in and abolished by brief exposure to Ca2+-free seawater. However, unl ike vertebrate hair bundles, anemone hair bundles appear to be insensi tive to amiloride since vibration-dependent discharge of nematocysts i s unaffected by up to mM amiloride. Thus, anemone hair bundles may ser ve as a useful model system for vertebrate hair bundles with the inter esting feature of being insensitive to amiloride.