Cell-type–specific roles of Na ⁺ /K ⁺ ATPase subunits in Drosophila auditory mechanosensation

Abstract

Ion homeostasis is a fundamental cellular process particularly important in excitable cell activities such as hearing. It relies on the Na + /K + ATPase (also referred to as the Na pump), which is composed of a catalytic α subunit and a β subunit required for its transport to the plasma membrane and for regulating its activity. We show that α and β subunits are expressed in Johnston's organ (JO), the Drosophila auditory organ. We knocked down expression of α subunits (ATPα and α-like) and β subunits (nrv1, nrv2, and nrv3) individually in JO with UAS/Gal4-mediated RNAi. U sing the energy of ATP hydrolysis, the Na pump extrudes cytoplasmic Na + (out) and extracellular K + (in) in a 3:2 ratio and maintains the gradient of these cations across the membrane (1, 2), thus controlling the electrolytic and fluid balance in the cells and organs throughout the body (1). Among its other functions, the Na pump helps maintain the resting potential of cells, regulates cellular volume, and facilitates transport of solutes in and out of cells. Ion homeostasis of most biological systems depends on the Na pump. In the auditory system, this pump has been linked to the maintenance of the inner ear osmotic balance (3). The scala media of the inner ear is filled with a K + -rich extracellular fluid known as endolymph, which is essential for preserving the sensory structures and supporting transduction. Maintaining the endolymph homeostasis is critical to sustain auditory functions. Loss of endolymphatic balance causes collapse of the endolymphatic compartment, leading to hearing loss in mammals (4). K + channels and pumps, including the Na pump, ensure proper cycling and secretion of K + ions in the stria vascularis cells of the cochlea. The Na pump has also been linked to age-related hearing loss (5) and Ménière disease (6). A detailed functional analysis of this pump is therefore necessary to gain insight into the molecular physiology of hearing loss resulting from loss of auditory ionic homeostasis.Although vertebrate and invertebrate auditory systems differ structurally, they evolved from the same primitive mechanosensors (7,8), and there are striking developmental genetic similarities between the two lineages. The fly auditory organ, Johnston's organ (JO), is a chordotonal organ (cho) housed in the second antennal segment (9). The JO comprises an array of ∼250 auditory units or scolopidia. Each scolopidium comprises two to three ciliated sensory neurons associated with several support cells. These bipolar neurons are monodendritic with a single distal cilium and a proximal axon (Fig. 1A). The scolopale cell, a principal support cell, encloses the neuronal dendrites in a fluid-filled lumen, the scolopale space. This fluid, the receptor lymph, resembles cochlear endolymph and, like the endolymph, is believed to be rich in K + ions (7). The scolopale cells are structurally enforced with actin-based scolopale rods. Auditory mechanosensation involves the transduction of the mechanical sound stimulus (10) through the rotation of distal...

Ecdysone regulates morphogenesis and function of malpighian tubules in Drosophila melanogaster through EcR-B2 isoform

“…(Na þ /K þ )-ATPase, an electrogenic pump is responsible for maintaining the balance of Na þ and K þ in almost all animal cells. Na þ /K þ -ATPase is critical to a variety of physiological processes like osmoregulation, cell volume regulation, transport of certain amino acid and sugar and maintenance of membrane excitability (Ianowski and O'Donnell, 2004, Verma and Tapadia, 2014, Roy et al, 2013. Direct correlation of Na þ /K þ -ATPase levels and Na þ concentration was rather surprising in the present study, but it is in agreement with earlier reports where reduced levels of (Na þ /K þ )-ATPase resulted in reduced Na þ (Davis et al, 1995;Verma and Tapadia, 2014).…”

“…(Na þ / K þ )-ATPase is a channel protein conserved from lower to higher organisms and plays a very important function in regulation of ionic balance in the cells (Roy et al, 2013). In adult and 3rd instar MTs, (Na þ /K þ )-ATPase has been reported to localize to the basolateral surface (Torrie et al, 2004;Verma and Tapadia, 2014), but due to absence of any report in 1st instar, we observed the expression of (Na þ /K þ )-ATPase in these larval MTs first.…”

Physiological, anatomical, and behavioral changes after acoustic trauma in Drosophila melanogaster

“…S2), to acoustic trauma and measured SEPs. Na + /K + ATPase is expressed in JO scolopidia where it likely regulates ion homeostasis (23). We hypothesized that mutant heterozygote JO neurons would be more severely affected by constitutive activity driven by the trauma stimulus, and demonstrate a higher sensitivity to trauma-induced metabolic stress.…”

“…Although evoked potential amplitudes were restored after 7 d, the latency of these potentials did not fully recover and we found significant changes in JO neural mitochondrial morphology. We also tested mutant flies with a reduced copy number of nervana 3 (nrv3) encoding a Na + /K + ATPase β subunit expressed in JO neurons (23). We hypothesized that compromised JO ionic homeostasis would confer susceptibility to noise trauma.…”

Brain Proteomics of Anopheles gambiae

“…The protein has been extensively studied in various organisms such as humans and drosophila, highlighting its importance in maintaining normal neuronal functions in an organism. Mutational studies and targeted knockdown studies have revealed that perturbations in the Na/K ATPase can lead to severe dysfunction in behavior, neuronal excitability, and defects in auditory mechanosensation (Roy et al, 2013), visual and motor sensory system (Palladino et al, 2003). Molecular characterization of the protein in gambiae is yet to be described.…”