The major delayed rectifier in both Drosophila neurons and muscle is encoded by Shab

Abstract

The delayed rectifier K+ current in Drosophila is similar to the classical delayed rectifier, originally described by Hodgkin and Huxley. Drosophila provides unique tools of mutant analysis to unambiguously determine the genetic identity of this native K+ current. We identified the Shab gene as the exclusive gene underlying delayed rectifier currents in both muscle and neurons. In muscles, a genetic mutation of Shab removes virtually all the whole cell delayed rectifier current (IK), while leaving unaltered the transient A-current encoded by the Shaker gene. In neurons, the Shab mutation also removes the bulk of IK, but leaves unaltered the transient A-current encoded by the Shal gene. Although most of the delayed rectifier current is the product of the Shab gene, the Shaw gene contributes a small “leak” current to most neurons and muscle cells. Thus, in contrast to the A-currents which are encoded by different genes in muscle and neuronal cell bodies (Shaker and Shal, respectively), the predominant IK in both muscle and neurons is encoded by the same gene (Shab). With the genetic identity of IK confirmed, all of the major K+ currents in embryonic Drosophila neurons and muscle are now known.

Distinct Frequency-Dependent Regulation of Nerve Terminal Excitability and Synaptic Transmission by IA and IK Potassium Channels Revealed by Drosophila Shaker and Shab Mutations

“…Sh I A undergoes rapid inactivation with a slower recovery time course and could be progressively removed during rapid repetitive depolarizing pulses (Baukrowitz and Yellen 1995). In contrast, inactivation of Shab I K is limited and slow, with more rapid recovery kinetics (Wu and Haugland, 1985;Tsunoda and Salkoff, 1995;Singh and Singh, 1999). As summarized in Figure 8, our data indicate that Sh I A undergoes cumulative inactivation during repetitive depolarization, leading to frequency-dependent facilitation of synaptic transmission.…”

Presynaptic Recordings fromDrosophila: Correlatin of Macroscopic and Single-Channel K+Currents

“…We therefore attributed the current difference to a small steady-state component of I A (which we could also observe at the single-channel level) rather than to an effect of the prepulse potential on I K . Most of the delayed K ϩ current in embryonic muscle fibers and neurons is attributable to Shab (Tsunoda and Salkoff, 1995b). Shab channels have a unitary conductance of 11 pS, exhibit bursting behavior, and produce a slowly inactivating ensemble average current.…”

“…embryonic and larval neurons (Solc and Aldrich, 1988;Tsunoda and Salkoff, 1995b). In this report the transient and delayed K ϩ currents will be referred to as I A and I K , respectively, notwithstanding that these terms refer to a general type rather than to a single unique current (see Discussion).…”

Shab K+channel slow inactivation

“…This has occurred in spite of a wealth of evidence indicating significant roles of Shab channels in membrane excitability, for example in action potential repolarization, and repeated spiking in a variety of Drosophila muscle and neural cells, as well as in cardiac beat frequency. [37][38][39][40][41][42][43] Clearly, in order to best understand the role of Shab in cell physiology, knowledge of its inactivation gating is required. Additionally, this will undoubtedly increase our understanding of inactivation mechanisms and pore dynamics of Kv channels.…”