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

Abstract

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 (K_ir), suggesting that K_ir in HCs may be a candidate for modulating seasonal changes. K_ir channel function depends on the plasma membrane phospholipid, PIP₂, to which it is bound. However, it remains unclear whether the PIP₂-K_ir channel interaction contributes to regulation of K_ir in goldfish HCs. Using perforated patch voltage-clamp recording, we identified K_ir current by inhibition with cesium (Cs⁺) and compared peak inward K_ir 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 K_ir channels. To examine the role of PIP₂ in regulating K_ir, tamoxifen or activation of phospholipase C by m-3M3FBS were used to disrupt the PIP₂-K_ir channel interaction and subsequently reduced K_ir current. Spermine, through strengthening the PIP₂-K_ir interaction, reduced the inhibitory effects of tamoxifen. Additionally, in current-clamp recordings, HCs treated with m-3M3FBS displayed a depolarized membrane potential (V_m) and a decrease in spontaneous Ca²⁺-based action potentials. We demonstrate that K_ir activity is seasonally regulated in goldfish HCs and that K_ir 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.