Functional Roles of Two-Pore Potassium Channels in the Rat Suprachiasmatic Nucleus Neurons

The circadian firing activity of hypothalamic suprachiasmatic nucleus (SCN) clock neurons allows them to control the circadian rhythms in mammals. One central issue is the origins of this firing rhythm. While the firing rate may depend on intrinsic excitability and input-driven activity, the SCN neurons maintain circadian firing even in isolation, suggesting an origin of circadian variation in intrinsic excitability. In SCN neurons, the averaged resting potentials (~-60 mV) are ~20 mV more negative to the firing threshold (~-40 mV). As such, to initiate an action potential the membrane potential must spontaneously rise from resting level to reach firing threshold, subject to voltage fluctuations. In other words, channels (and transporters) responsible for regulating resting potentials and interspike potentials are particularly important in setting the intrinsic excitability. Among these channels, the leak K+ channels mostly determine the background conductance and resting potential, and also help to regulate the interspike potential. The two-pore domain K+ (K2P) channels open at rest to act as leak K+ channels. The mammalian K2P family has 16 members divided to six subfamilies: TWIK (TWIK1, TWIK2, KCNK7), TASK (TASK1, TASK3, TASK5), TREK (TREK1, TREK2, TRAAK), TALK (TALK1, TALK2, TASK2), THIK (THIK1, THIK2) and TRESK (TRESK1, TRESK2). Functional K2P channels are formed as homodimers, but functional heterodimers between TASK1 and TASK3 have been demonstrated in heterologous expression system and in native neurons. In situ hybridization and RT-PCR analysis indicate the presence of TASK1, TASK3, and TRAAK in SCN. This three years project aims to determine the functional roles of K2P channels in SCN neurons. We will first determine the role of K2P channels in the leak K+ conductance and in mediating cholinergic inhibition of SCN excitability. We will then determine the receptor and signaling mechanisms underlying the two unusual cholinergic effects (activation and hyperpolarizing shift in the IV relations) on K2P channels. Membrane potentials and currents will be recorded with the whole-cell and perforated-patch techniques in current- and voltage-clamp modes. Completion of this project should advance our understanding as to the functional roles of K2P channels in the central clock neurons, and may even elucidate two novel mechanisms of K2P modulation.

Project ID:PC9808-0549
External Project ID:NSC98-2320-B182-025-MY3