NATURE AND CONTROL OF CHLORIDE TRANSPORT IN INSECT ABSORPTIVE EPITHELIA

Insect epithelia most commonly absorb from KCl-rich, low Na+ fluids. T his is true of the locust hindgut, which is functionally analogous to vertebrate kidney tubules. Active absorption of Cl- at the apical memb rane is the predominant transport process giving rise to a large short -circuit current (I-sc) after stimulation by neuropeptides (CTSH, ITP) via cAMP as second messenger. This Cl- transport is not coupled to or driven secondarily by Na+, K+, HCO3-, Ca2+, or Mg2+ movements. An api cal V-type H+ ATPase acidifies the hindgut lumen but at a rate that is 10-15% of Cl-dependent I-sc. The evidence to date as to whether the r esulting large apical proton gradient is used to drive Cl- transport s econdarily by an apical H+/Cl- symport is mixed. Thus a primary mechan ism of Cl- absorption remains an alternative possibility. The complete primary structure of a large neuropeptide stimulant (ITP: 72 amino ac ids) of locust ileal Cl- transport has recently been deduced from its cDNA. This is the first putative insect neuropeptide hormone shown to stimulate ion transport across absorptive epithelia for which the prim ary sequence has been deduced. (C) 1996 Wiley-Liss, Inc.