AJP - Regulatory, Integrative and Comparative Physiology, Vol 257, Issue 5 967-R972, Copyright © 1989 by American Physiological Society
Membrane dynamics in insect malpighian tubules
T. J. Bradley
Department of Developmental and Cell Biology, University of California, Irvine 92717.
Urine formation in insects occurs in the Malpighian tubules by means of
active ion transport and osmotically coupled water flow. The rates of urine
formation can vary with time and can be modulated by diuretic hormones,
developmental events, and intracellular parasitism. This paper reviews a
number of recent studies in which it has been demonstrated that variations
in transport rate are associated with substantial changes in tubule
ultrastructure in the form of membrane insertion into and deletion from the
apical microvilli. The principal driving force for fluid movement in
Malpighian tubules is thought to be a common cation pump located in the
apical membranes. It is proposed that modulation of the apical microvillar
membrane may reflect regulation by the cells of the number of common cation
pump units involved in fluid secretion.
