Molecular physiology on ion transport sytems in silkworms

鳞翅目昆虫中肠(消化道的主要部分)是跨上皮交换各种离子溶质、维持细胞活动和组织功能的中心和不可或缺的组织(S)。我们研究了这种机制，以了解家蚕系统中的离子动态平衡和渗透调节。结果：(1)用抗V-ATPase特异性抗体进行免疫细胞化学研究。在蚕体中，V-ATPase存在于中肠、马氏管、唾液腺和丝腺中。V-ATPase位于细胞表面，提示V-ATPase是质膜型的，而不是膜内型的。(2)在蚕丝腺中，V-ATPase似乎有助于在腺腔内产生酸性环境。这与中肠腔形成了强烈的对比，中肠腔产生极高的碱度(pH 11-12)。(3)丝腺V-ATPase在V-ATPase的共同亚基上与其他动物的V-ATPase非常相似。(4)中肠K+/氨基酸转运体是相当不稳定的蛋白质，很难纯化。其分子性质尚不清楚。(5)丝腺是丝蛋白合成和分泌的高活性组织。这意味着组织需要来自血淋巴的大量氨基酸来合成丝蛋白。因此，研究丝腺中的K+/氨基酸转运体已成为近期的研究课题。这有望成为鉴定K+/转运蛋白分子的突破口(S)。

Insect midgut in Lepidoptera (the main part of the alimentary canal) is a central and indispensable tissue to exchange various ionic solutes across the epithelia and to maintain the cellular activity and the tissue functions (s). We have investigated such a mechanism to understand the ionic homeostasis and osmoregulation in the silkworm system. Results ar as follows :(1) Immunocytochemical studies were done with the specific anitibody against V-ATPase. In silkwrms, V-ATPase can be detected in the midgut, the Malpighian tubules, the salivary gland and the silk gland. V-ATPase in each tissue was located at the cell surface, suggesting that silkworm V-ATPase is a plasma membrane-type not an endomenbrane-type.(2) In the silk gland, V-ATPase seems to contribute to produce an acidic milieu in the glandular lumen. This shows highly contrast to the midgut lumen, which produce an extremely high alkalinity (pH 11-12).(3) The silk gland V-ATPase is quite similar to other animal V-ATPases in the common subunits of V-ATPase.(4) K+/amino acid symporter in the midgut was rather labile protein and hard to purify. Its molecular nature still remains unknown.(5) The silk gland is highly active tissue for silk protein syntesis and secretion. This implies that the tissue needs much supply of amino acids from the haemolymph to synthesize the silk protein. Thus, it is coming up as the quite near future subject to survey the K+/amino acid symporter in the silk gland. This would be expected as the breakthrough for identifing the K+/symporter molecule (s).