K⁺ channel reorganization and homeostatic plasticity during postembryonic development: biophysical and genetic analyses in acutely dissociated Drosophila central neurons

Abstract

Intrinsic electric activities of neurons play important roles in establishing and refining neural circuits during development. However, how the underlying ionic currents undergo postembryonic reorganizations remains largely unknown. Using acutely dissociated neurons from larval, pupal, and adult Drosophila brains, we show drastic re-assemblies and compensatory regulations of voltage-gated (I_Kv) and Ca²⁺-activated (I_K(Ca)) K⁺currents during postembryonic development. Larval and adult neurons displayed prominent fast-inactivating I_Kv, mediated by the Shaker (Sh) channel to a large extent, while in the same neurons I_K(Ca) was far smaller in amplitude. In contrast, pupal neurons were characterized by large sustained I_Kv and prominent I_K(Ca), encoded predominantly by the slowpoke (slo) gene. Surprisingly, deletion of Sh in the Sh^M null mutant removed inactivating, transient I_Kv from large portions of neurons at all stages. Interestingly, elimination of Sh currents was accompanied by upregulation of non-Sh transient I_Kv. In comparison, the slo¹ mutation abolished the vast majority of I_K(Ca), particularly at the pupal stage. Strikingly, the deficiency of I_K(Ca) in slo pupae was compensated by the transient component of I_Kv mediated by Sh channels. Thus, I_K(Ca) appears to play critical roles in pupal development and its absence induces functional compensations from a specific transient I_Kv current. While mutants lacking either Sh or slo currents survived normally, Sh;;slo double mutants deficient in both failed to survive through pupal metamorphosis. Together, our data highlight significant reorganizations and homeostatic compensations of K⁺currents during postembryonic development and uncover previously unrecognized roles for Sh and slo in this plastic process.

Keywords:

• Whole-cell current
• Ca²⁺-activated K⁺ current
• larva
• pupa
• adult
• voltage-gated K⁺ current
• Sh channels
• slo channels

Acknowledgements

We dedicate this manuscript to the special issue in honor of the lifetime achievements of Dr. Barry Ganetzky. His early pioneering work on Sh and slo has engendered several active research areas that continues to produce exciting new findings. This study based on hundreds of Sh and slo neurons is a testimony of how he profoundly influenced the development of this important research field in the past decades.

Funding

This study was supported by the Knowledge Innovation Project from the Chinese Academy of Sciences (KSCX2-YW-R-35) and the National Basic Research Program of China (No. 2006CB500803) to T.-L. X., US NIH Grants GM088804 and AG051513 to C.-F. W., DA032283 to W.-D.Y., and OD011103 to New England Primate Research Center, Harvard University. C.-F. W. was also supported by the Wang Kuancheng Scholarship of the Chinese Academy of Sciences while conducting research at the University of Science and Technology of China. We thank Dr. Z.-R. Wang for comments on the manuscript, Q. Wang and H. Lu for technical assistance, and T. Patience for assistance in manuscript preparation.

Disclosure statement

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.