Seasonal regulation and PIP2 dependence of inwardly rectifying potassium channels (Kir) in retinal horizontal cells of goldfish (Carassius auratus).

Many species face extreme changes in their environment throughout the year, during which time they must modify their neuronal activity to survive. Horizontal cells (HCs) are interneurons in the goldfish (Carassius auratus) retina that demonstrate seasonal changes in membrane structure and excitability. Excitability in neurons is strongly influenced by inwardly rectifying potassium channels (Kir), suggesting that Kir in HCs may be a candidate for modulating seasonal changes. Kir channel function depends on the plasma membrane phospholipid, PIP2, to which it is bound. However, it remains unclear whether the PIP2-Kir channel interaction contributes to regulation of Kir in goldfish HCs. Using perforated patch voltage-clamp recording, we identified Kir current by inhibition with cesium (Cs+) and compared peak inward Kir current density in goldfish HCs isolated during the summer and winter months. Significantly more current was inhibited by Cs+ in winter HCs, suggesting more open Kir channels. To examine the role of PIP2 in regulating Kir, tamoxifen or activation of phospholipase C by m-3M3FBS were used to disrupt the PIP2-Kir channel interaction and subsequently reduced Kir current. Spermine, through strengthening the PIP2-Kir interaction, reduced the inhibitory effects of tamoxifen. Additionally, in current-clamp recordings, HCs treated with m-3M3FBS displayed a depolarized membrane potential (Vm) and a decrease in spontaneous Ca2+-based action potentials. We demonstrate that Kir activity is seasonally regulated in goldfish HCs and that Kir is dependent upon PIP2. Our results suggest PIP2 as a potential target for coordinating seasonal changes in the activity of neurons in the goldfish retina.