Molecular physiology on ion transport sytems in silkworms

鳞翅目昆虫的中肠（消化道的主要部分）是跨上皮交换各种离子溶质，维持细胞活性和组织功能必不可少的中心组织。我们研究了这一机制，以了解家蚕系统中的离子稳态和渗透调节。结果如下：(1)用特异性抗体对V-ATPase进行免疫细胞化学研究。在家蚕中肠、马氏小管、唾液腺和丝腺中均可检测到v - atp酶。各组织中V-ATPase均位于细胞表面，提示家蚕V-ATPase为质膜型而非膜内型。(2)在丝腺中，v - atp酶似乎有助于在腺腔中产生酸性环境。这与产生极高碱度（pH值11-12）的中肠腔形成鲜明对比。(3)丝腺V-ATPase与其他动物V-ATPase在共同亚基上非常相似。(4)中肠K+/氨基酸同调体是一种较不稳定的蛋白质，纯化难度较大。它的分子性质仍然未知。(5)丝腺是丝蛋白合成和分泌的高活性组织。这意味着组织需要从血淋巴中获得大量氨基酸来合成丝蛋白。因此，研究蚕丝腺中K+/氨基酸同向转运体是近期的研究课题。这将被认为是鉴定K+/同调分子的突破。

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).