Voltage-gated and two-pore-domain potassium channels in murine spiral ganglion neurons

The systematically varied firing features of spiral ganglion neurons provide an excellent model system for the exploration of how graded ion channel distributions can be used to organize neuronal firing across a population of neurons. Elucidating the underlying mechanisms that determine neuronal response properties requires a complete understanding of the combination of ion channels, auxiliary proteins, modulators, and second messengers that form this highly organized system in the auditory periphery. Toward this goal, we built upon previous studies of voltage-gated K⁺-selective ion channels (Kv), and expanded our analysis to K⁺-selective leak channels (KCNK), which can play a major role in setting the basic firing characteristics of spiral ganglion neurons. To begin a more comprehensive analysis of Kv and KCNK channels, a screening approach was employed. RT-PCR was utilized to examine gene expression, the major results of which were confirmed with immunocytochemistry. Initial studies validated this approach by accurately detecting voltage-dependent K⁺ channels that were documented previously in the spiral ganglion. Furthermore, an additional channel type within the Kv3 family, Kv3.3, was identified and further characterized. The major focus of the study, however, was to systematically examine gene expression levels of the KCNK family of K⁺-selective leak channels. These channel types determine the resting membrane potential which has a major impact on setting the level of neuronal excitation. TWIK-1, TASK-3, TASK-1, and TREK-1 were expressed in the spiral ganglion; TWIK-1 was specifically localized with immunocytochemistry to the neuronal somata and initial processes of spiral ganglion neurons in vitro.