An antidiuretic factor in the forest ant: purification and physiological effects on the Malpighian tubules

Formica polyctena antidiuretic factor (FopADF) was purified from a 15% trif luoroacetic acid (TFA) extract of the abdomens of 150,000 worker ants. Afte r solid phase extraction of the crude extract and reversed-phase HPLC on tw o C-18 columns, an antidiuretic factor was isolated. Tested at a concentrat ion of 1.0 ant-equivalents/mul (ant-eq/mul), the factor reversibly inhibite d fluid secretion of isolated Malpighian tubules to 29+/-5% (mean+/-SE, n=2 4) of the control value. The same concentration of FopADF reversibly depola rized both the basolateral membrane potential (V-bl), from -21+/-2 mV to -3 +/-1 mV (n=5), and the apical membrane potential (V-ap), from -65+/-5 mV to -20+/-5 mV (n=5). Similar effects on fluid secretion and V-ap were caused by a TFA extract of the haemolymph of ants with non-secreting tubules. Unfo rtunately, further purification of FopADF on a C-4 column led to a loss of activity in the fluid secretion assay. This is the first time an endogenous antidiuretic factor acting directly on Malpighian tubules has been partial ly purified and shown to depolarize the tubule cell membranes. (C) 2000 Els evier Science Ltd. All rights reserved.