Modulation of the frequency response of Shaker potassium channels by the quiver peptide suggesting a novel extracellular interaction mechanism.

Recent studies have indicated that the Shaker potassium channel regulates sleep in Drosophila. The Drosophila quiver (qvr) gene encodes a novel potassium channel subunit that modulates the Shaker potassium channel. The Qvr peptide contains a signal sequence for extracellular localization and may regulate a unique feature of the Shaker I(A) current that confers special neuronal excitability patterns. Thus, studies of the Shaker channel properties in the qvr mutant background should provide an opportunity to uncover a new form of physiologic modulation of potassium channels. We have begun to investigate the impact of qvr protein on the Shaker channel properties and its implications in synaptic function in vivo. We studied synaptic transmission at the larval neuromuscular junction and characterized the transient potassium current I(A) in larval muscles. We identified two different functional states of I(A) in qvr larval muscles, as reflected by two distinct components, I(AF) and I(AS), differing in their kinetics of recovery from inactivation and sensitivity to a K(+) channel blocker. Correspondingly, qvr mutant larvae exhibit multiple synaptic discharges following individual nerve stimuli during repetitive activity.