Drosophila cacophonyChannels: A Major Mediator of Neuronal Ca²⁺Currents and a Trigger for K⁺Channel Homeostatic Regulation

Abstract

The cacophony (cac) locus in Drosophila encodes a Ca 2ϩ channel ␣ subunit, but little is known about properties of cac-mediated currents and functional consequences of cac mutations in central neurons. We found that, in Drosophila cultured neurons, Ca 2ϩ currents were mediated predominantly by the cac channels. The cac channels contribute to low-and high-threshold, fast-and slow-inactivating types of Ca 2ϩ currents, take part in membrane depolarization, and strongly activate Ca 2ϩ -activated K ϩ current [I K(Ca) ]. In cac neurons, unexpectedly, voltage-activated transient K ϩ current I A is upregulated to a level that matches I K(Ca) reduction, implicating a homeostatic regulation that was mimicked by chronic pharmacological blockade of Ca 2ϩ currents in wild-type neurons. Among K ϩ channel transcripts, Shaker mRNA levels were preferentially increased in cac flies. However, Ca 2ϩ current expression levels remained unaltered in several K ϩ channel mutants, illustrating a key role of cac in developmental regulation of Drosophila neuronal excitability.

Temperature-Dependent Developmental Plasticity ofDrosophilaNeurons: Cell-Autonomous Roles of Membrane Excitability, Ca2+Influx, and cAMP Signaling

“…6 D, E) (cf. Peng and Wu, 2007b). Strikingly, both the transient and sustained components of Ca 2ϩ channel-mediated currents were upregulated in cultures grown at 30°C (Fig.…”

“…Wu et al, 1983;Wu and Haugland, 1985;Haugland and Wu, 1990;Zhong and Wu, 1993;Peng and Wu, 2007a). A Ca 2ϩ channel mutant, cacophony (cac s ), was examined (Peng and Wu, 2007b). Mutations affecting cAMP metabolism included dunce (dnc 1 ), which is defective in a cAMP-dependent phosphodiesterase (PDE), and rutabaga (rut 1 and rut 2 ), which is defective in an adenylate cyclase (AC) (Dudai et al, 1976;Byers et al, 1981;Livingstone et al, 1984;Tully and Quinn, 1985).…”

“…A patch-clamp amplifier (Axopatch 1B; Molecular Devices, Palo Alto, CA) and a computer in conjunction with an analog-to-digital (A/D)-D/A converter and pClamp software (version 5.5.1; Molecular Devices) were used to generate the current-and voltage-clamp commands and for data acquisition. For better isolation of Ca 2ϩ currents, Ba 2ϩ (20 mM) as well as Na ϩ and K ϩ channel blockers (10 nM TTX, 1 mM 4-AP, 2.5 mM TEA, and 0.05 mM quinidine) were added to the bath saline, and K ϩ in the pipette solution was replaced by Cs ϩ (Peng and Wu, 2007b). Voltage-activated K ϩ currents were measured in the presence of Na ϩ and Ca 2ϩ channel blockers in the bath (10 nM TTX and 0.2 mM Cd 2ϩ ).…”

“…Because neuronal activity facilitates Ca 2ϩ influx through voltage-gated Ca 2ϩ channels to influence intracellular Ca 2ϩ dynamics, we examined the effects of a Ca 2ϩ channel mutation, cac, that greatly reduces Ca 2ϩ currents in cultured giant neurons (Peng and Wu, 2007b) and depolarization-induced Ca 2ϩ transients (data not shown). The cac mutation by itself did not alter growth cone sizes and arborization indices but blocked the ability of high temperature to increase these morphological indicators (Fig.…”

“…Our study reveals the role of Ca 2ϩ channels in the temperature-promoted neuronal growth. Mutations of the cac locus, encoding a voltage-gated Ca 2ϩ channel, severely reduce neuronal Ca 2ϩ currents (Peng and Wu, 2007b) and suppress temperature-induced neurite overbranching and growth cone enlargement (Fig. 7).…”