果蠅的聽覺系統(tǒng)與人類很相似,，Iowa大學(xué)的生物學(xué)家Daniel Eberl及其同事利用果蠅的“情歌”進(jìn)行研究,，發(fā)現(xiàn)聽覺系統(tǒng)擁有與汽車蓄電池類似的機(jī)制。這項(xiàng)研究作為封面文章發(fā)表在最近一期的美國(guó)國(guó)家科學(xué)院院刊PNAS雜志上,。
對(duì)于可興奮細(xì)胞的活性（聽覺細(xì)胞等）來說,，離子內(nèi)穩(wěn)態(tài)特別重要,，而這依賴于一種相當(dāng)于Na+/K+泵的蛋白——Na+/K+ ATPase,。該蛋白由一個(gè)α亞基和一個(gè)β亞基組成,，也常被簡(jiǎn)稱為鈉泵。研究人員發(fā)現(xiàn),，在果蠅耳部專門的支持細(xì)胞（scolopale細(xì)胞）中,，這種鈉泵高度表達(dá)。
在果蠅的聽覺系統(tǒng)中scolopale細(xì)胞是很重要的,，它環(huán)繞著果蠅耳部的感覺末梢,，形成密閉的細(xì)胞外隔室（scolopale space）。研究人員指出,，果蠅聽覺系統(tǒng)的這種小隔室與蓄電池作用相似,，需要先充電然后才能在系統(tǒng)中釋放電子。充電完成后,，這種隔室釋放出的離子就會(huì)通過感覺末梢上的膜通道,，這些通道是由聲音激活而短暫開啟的。
果蠅的“情歌”是指一種翅膀振動(dòng)發(fā)出的聲音,，研究人員巧妙利用這一求愛之聲,，根據(jù)果蠅是否能聽見這種聲音，來研究其聽覺系統(tǒng)的電反應(yīng),。為此,，研究人員在果蠅的觸須里插入了微小的電極，隨后他們用電腦播放果蠅的求愛之歌,，并對(duì)其間的電反應(yīng)進(jìn)行檢測(cè),。
研究顯示，鈉泵在scolopale細(xì)胞中有著特別重要的作用,，負(fù)責(zé)幫助細(xì)胞向隔室中補(bǔ)充正確的離子,，如果鈉泵出現(xiàn)故障就會(huì)導(dǎo)致果蠅喪失聽力。
人類耳部的聽覺系統(tǒng)也存在著一種隔室——中階（scala media）,，其作用也是向耳部的感覺細(xì)胞釋放離子,。研究人員指出，果蠅和人類的聽覺系統(tǒng)有許多相似之處,。在果蠅模型中研究耳部離子平衡所需的各項(xiàng)元件,，有助于人們進(jìn)一步了解人類的聽覺系統(tǒng)。(生物谷Bioon.com)
doi: 10.1073/pnas.1208866110
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Cell-type–specific roles of Na+/K+ ATPase subunits in Drosophila auditory mechanosensation
Madhuparna Roy, Elena Sivan-Loukianova, and Daniel F. Eberl1
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. ATPα shows elevated expression in the ablumenal membrane of scolopale cells, which enwrap JO neuronal dendrites in endolymph-like compartments. Knocking down ATPα, but not α-like, in the entire JO or only in scolopale cells using specific drivers, resulted in complete deafness. Among β subunits, nrv2 is expressed in scolopale cells and nrv3 in JO neurons. Knocking down nrv2 in scolopale cells blocked Nrv2 expression, reduced ATPα expression in the scolopale cells, and caused almost complete deafness. Furthermore, knockdown of either nrv2 or ATPα specifically in scolopale cells causes abnormal, electron-dense material accumulation in the scolopale space. Similarly, nrv3 functions in JO but not in scolopale cells, suggesting neuron specificity that parallels nrv2 scolopale cell–specific support of the catalytic ATPα. Our studies provide an amenable model to investigate generation of endolymph-like extracellular compartments.
