Excretion in the house cricket Acheta domesticus: Effects of diuretics on the structure of the mid-tubule

Most structural studies of insect Malpighian tubules focus on freshly dissected tissue, which is in fact stimulated by diuretic factors. In this study, we examine tubules from the house cricket Acheta domesticus in four discrete secretory states: control (freshly dissected); unstimulated (held in vitro for 90 min prior to fixation); corpus cardiacum-stimulated (held in vitro for 60 min, then stimulated with corpus cardiacum homogenates for 30 min prior to fixation); and cAMP-stimulated (held in vitro for 60 min, then stimulated with dibutyryl cAMP for 30 min prior to fixation). In unstimulated tubules, we see a reduction in vacuolization and a near-complete collapse of the basolateral infolds. Stimulated tubules show several major structural shifts: mitochondria are darkly stained with well-defined cristae, there is extensive vacuolization of the tissue and expansion of the basolateral spaces, and the CaPO₄ spherites appear to be ejected into the lumen. cAMP-stimulated tubules showed the most pronounced structural changes, including the presence of a newly reported ultrastructural feature for A. domesticus Malpighian tubules, referred to here as paracrystalline arrays, which appear as stacks of membrane localized in the perinuclear region. © 1996 Wiley-Liss, Inc.