Abstract
Purpose :
The frequency of action potentials in retinal ganglion cells (RGCs) exhibits adaptation to the increment of brightness or darkness instead of increasing unrestrictedly. The intrinsic mechanisms for adaptation are not completely understood. The two-pore-domain potassium channels (K2P) provide background K+ currents to regulate action potential generation/maintenance, representing a potential mechanism for adaptation. However, the functional roles of K2P in retina remain largely unexplored. In the current research, we studied the acid-sensitive K2P, TASK-3 (Tandem pore domain acid-sensitive K channel 3), in RGCs.
Methods :
We used RNAscope, a new-generation mRNA in-situ hybridization technique to map the transcription of TASK-3 at the retina of adult C57BL/6 mice. RGCs were recorded by whole-cell patch clamping on flat-mounted mice retina. Intrinsic properties of RGCs were measured using TASK-3 specific inhibitor PK-THPP (3 mM) in WT and TASK-3 knockout (KO) mice. Action potentials (APs) were generated via step currents injection. PK-THPP-sensitive currents were isolated using drug cocktails including TTX (500 nM) and 4-AP (5 mM).
Results :
Kcnk9 (TASK-3) and Rbfox3 (NeuN) mRNA were observed at ganglion cell layer and the inner part of inner nuclear layer. Almost all RGCs expressed TASK-3. In electrophysiological experiments, more numbers of APs were elicited upon relatively small current injections in the treatment with PK-THPP than with vehicle control. However, less numbers of APs and more accommodation were observed upon relatively large current injections in the treatment of PK-THPP than vehicle control. In PK-THPP group, AP amplitudes decreased significantly (P < 0.0001, N = 54 cells); AP widths were significantly broader (P = 0.0004); the maximal rise slope and maximal decay slope of APs were decreased significantly (both rise and decay: P < 0.0001); AP thresholds declined slightly but significantly (P = 0.0144); the input resistance of RGCs enhanced significantly (P = 0.0014). PK-THPP-sensitive currents were strongly outwardly rectifying which represented typical K2P-mediated K+ currents. Similar results were recorded in TASK-3 KO mice.
Conclusions :
K2P channel TASK-3 is highly expressed in mouse RGCs. TASK-3-mediated K+ currents contribute to the excitability and APs accommodation of RGCs which may potentially adjust visual adaptation in mouse retina.
This is a 2020 ARVO Annual Meeting abstract.