IK channel confers fine-tuning of rod bipolar cell excitation and synaptic transmission in the retina

Abstract

During retinal visual processing, rod bipolar cells (RBCs) transfer scotopic signals from rods to AII amacrine cells as second-order neurons. Elucidation of the RBC excitation/inhibition is essential for understanding the visual signal transmission. Although excitation and extrinsic inhibitory mechanisms have been studied, intrinsic inhibitory mechanisms remain unclear. We focused on RBCs prominent K+ current, which exhibits voltage and Ca2+ dependence. We isolated and confirmed intermediate-conductance Ca2+-activated K+ channels (IK) and in RBCs using the patch-clamp method with IK inhibitors (clotrimazole and TRAM34). The regulation of the IK current primarily relies on Ca2+ influx via low-threshold Ca2+ channels during RBC excitation. It mediates RBC repolarization and oscillation, enabling fast and transient synaptic transmission to AII amacrine cells. Our findings highlight the unique role of the IK channel in RBC, suggesting that it plays a critical role in the scotopic pathway by fine-tuning RBC activity.