MECHANOTRANSDUCTION OF HAIR BUNDLES ARISING FROM MULTICELLULAR COMPLEXES IN ANEMONES

Sea anemones are among the simplest animals to use hair bundles to det ect vibrations. Although we previously found anemone bundles to be mor phologically similar to vertebrate hair bundles, only indirect evidenc e implicated anemone bundles in mechanotransduction. Here, we test mec hanotransduction of these bundles using loose-patch current recording from apical membranes of cells at the base of deflected bundles. Step bundle deflection results in graded membrane currents that are inward in some cells (positive) and outward in other cells (negative). Positi ve responses range from 5 to 30 pA, abruptly saturate with stronger st imuli, and increase in duration with prolonged deflections. Negative r esponses range from 10 to 150 pA, show a logarithmic relation to stimu lus strength, and attenuate with prolonged deflections. Additionally, responses are reversibly inhibited by streptomycin. We present a model for anemone bundle mechanotransduction modified from the gating sprin g model for vertebrate mechanotransduction. Because anemone bundles co mprise stereocilia arising from a multicellular complex, we propose th at supporting cells on opposite sides of a bundle function as opposite ly polarized hair cells. Thus, deflection induces ion channels to open in cells on one side of the complex, while allowing channels to close in cells on the opposite side of the complex.