Ultrastructural changes in the malpighian tubules of the house cricket, Acheta domesticus, at the onset of diuresis: A time study

The Malpighian tubules (Mt) of insects are responsible for maintaining osmo tic homeostasis and eliminating waste from the hemolymph. When stimulated b y diuretic factors the tubule cells are able to transport extraordinary vol umes of fluid over short periods of time. We have been studying the changes that occur within the cells that accompany and facilitate this phenomenon. We present the ultrastructural changes that occur in the midtubule of the house cricket, Acheta domesticus, following exposure to the second messenge r analog, dibutyryl cAMP. over the period from 15-420 sec. Vacuolation of t he cytoplasm begins as early as 30 sec poststimulation with a significant i ncrease in vacuolation occurring after 120 sec. As expected, there is an in crease in the surface area of the basolateral membrane to facilitate the ra pid movement of fluid into the cells. Other ultrastructural changes noted t o accompany the onset of diuresis include the movement of mitochondria into areas adjacent to transport membranes, the vesiculation of Golgi, mobiliza tion of CaPO4 spherites, and a direct interaction of these spherites with a ctive mitochondria. We discuss several possible roles for these changes in terms of rapid fluid transport. (C) 2001 Wiley-Liss, Inc.