Sound stimulates labeling of polyphosphoinositides in the auditory organ of the noctuid moth.

The Noctuid moth possesses a simple auditory structure suitable for the investigation of biochemical correlates of sound stimulation in vivo. Stimulation with pulsed tones increased ?lP incorporation into polyphosphoinositides but not into ATP or other lipids. The effect was seen in the scoloparium (sensory structure) but not in the nodular sclerite, an adjacent nonsensory tissue. It was also not seen when the stimulus was a continuous t o n e , leading to adapta t ion of t he ac t ion poten t ia l . K e y words: Phospholipids-Phosphatidylinositol phosphate; biphosphate-Acoustic stimulation-Biopotentials. Molecular changes concomitant with the electrophysiological events in stimulated auditory receptors are as yet unknown, at least partly for the lack of a suitable experimental model. For our purpose, an auditory structure is needed in which the electrophysiological detail of its response is sufficiently well defined and simple to permit a correlation with biochemical findings. The ear of the Noctuid moth appears to meet these criteria. It is easily accessible and has a markedly simple morphology and electrophysiology. The sensory tissue, the scoloparium, contains two sensory cells along with a few supporting cells (Ghiradella, 1971). The sensory cells are true auditory receptors, of essentially similar, physiological characteristics (Suga, 1961; Adams, 1971; Roeder, 1971). Only two types of bioelectric activity are induced by sound stimulation in these primary sensory cells: the generator or receptor potential, tantamount to the transduction event in the denqritic ends, and the action potential in the axonal segments. The preparation thus seemed well suited for an investigation of the role of polyphosphoinositides in hearing processes. The polyphosphoinositides, phosphatidylinositol phosphate and phosphatidylinositol bisphosphate', are quantitatively minor phospholipids of eukaryotic cells, but the turnover of their monoesterified phosphate groups is very rapid, as shown by 32P radiotracer techniques. The rate of this turnover in neural tissue, the tissue in which these lipids primarily occur in mammals, is not invariant. Excitation of a variety of nerves and axons leads to changes in polyphosphoinositide metabolism (Birnberger et al., 1971; Schacht and Agranoff, 1972; Tret'jak et al., 1977; Abdel-Latif et al., 19781, and a phosphorylation and dephosphorylation cycle has been suggested as being associated with membrane permeability changes in axonal conduction (Griffin and Hawthorne, 1978; Kai and Hawthorne, 1969). In insects, polyphosphoinositides seem to have a widespread tissue distribution which includes nerves and sensory systems (Bridges, 1973; Kilian and Schacht, 1979). We have previously proposed a mechanism for the transduction of acoustic energy into a generator potential by regulation of phosphorylationdephosphorylation reactions in the receptor membrane by sound energy (Kilian and Schacht, 1977). The polyphosphoinositides were suggested as candidates for this scheme, also, because studies with aminoglycosidic antibiotics suggested a specific role for these lipids in auditory phenomena. A change in turnover of these lipids after administration of Address reprint requests to Dr. J . Schacht. Present address of P.L.K. is Department of Molecular Biology, Eastern Pennsylvania Psychiatric Institute, Philadelphia, Pa. 19129. Received July 2, 1979; accepted September 27, 1979. ' 1-(3-sn-Phosphatidyl)-~-myo-inositol 4-phosphate and 143sn-phosphatidyl)-D-myo-inositol 4,5-bis(phosphate).