Type I Spiral Ganglion Neurons (SGN) synapse onto cochlear inner hair cells, and constitute the majority of afferent fibres in the auditory nerve. In the absence of functional hair cells, SGN can be stimulated by cochlear implant electrodes to provide “electrical” hearing. Better characterisation of their biophysical properties may identify therapeutic targets for optimising auditory nerve sensitivity. SGN excitability has been shown to be set by a Dendrotoxin-K-sensitive low voltage-activating K+ current (1). Activity of Kv channels can be sensitive to binding of Phosphatidylinositol 4,5-bisphosphate, known as “PIP2” (2), and consequently PIP2 can be an important determinant of neuronal excitability. Here we have assessed the contribution of PIP2 signalling to SGN function. SGN from juvenile C57BL/6 mice (P12-P21) were cultured for 2-3 days in the presence of Brain Derived Neurotrophic Factor. Under control conditions ~70% (8/11) of SGN fired rapidly-adapting (“phasic”) action potentials under current clamp, and the remaining cells were slowly-adapting or non-adapting (“tonic” firing). ~20 % (2/11) exhibited spontaneous firing at the resting membrane potential. Pre-incubation for 1 hr at 37oC with 10 µM Wortmannin, an enzyme inhibitor of PIP2 production (3), reduced the prevalence of phasic firing to ~50% (12/23) and increased the prevalence of spontaneous activity to ~40% (10/23). The effects of Wortmannin treatment could be partially rescued by the intracellular application of diC8-PIP2, a non-metabolisable PIP2analogue (n=10). In separate experiments, SGN were depleted of membrane-bound PIP2 by transient exposure to a membrane-targeting palmitoylated peptide (“PalPeptide”) based on the putative PIP2 binding domain of the Kv7.2 channel (4). Bath application of 1-3 µM Pal-Peptide slowed adaptation in all cases (9/9). Under voltage clamp, 1 µM PalPeptide inhibited a low voltage-activated K+ current (77 ± 4% (mean ± SEM) measured at 2 minutes, n=6). This effect could be reduced significantly by intracellular application of diC8-PIP2 (41 ± 5%, n=7, P<0.001). This PalPeptide-sensitive current was also blocked by Dendrotoxin-K, identifying Kv1.1 as an important contributor. Other work from our lab has suggested Kv1.1 forms heteromeric channels with Kv1.2 in these cells (Smith et al, this meeting). PalPeptide inhibited membrane currents in HEK-293 cells expressing Kv1.1/Kv1.2 channels (55 ± 14%, n=4), and this effect was reduced by intracellular application of diC8-PIP2 (23 ± 7%, n=4). We suggest PIP2 binding may provide an adjustable brake on the output of the auditory nerve via its binding to Kv1-containing channels, and our observations identify phosphoinositide signalling as a novel therapeutic target in the cochlea.