Phosphate transport by locust rectum <i>in vitro</i>

Abstract

The rectal cuticle is permeable to H 2 PO 4 − , but much less so to HPO 4 2− . Everted rectal sacs of Schistocerca gregaria transport PO 4 from lumen to hemocoel side against large concentration and electrical differences. This active process is not caused by solvent drag and it obeys Michaelis–Menten kinetics. Entry of 32 PO 4 into rectal tissue from the lumen is inhibited by arsenate. Much of the 32 PO 4 is converted to organic forms in the tissue but these do not enter the hemocoel compartment. Net rates of PO 4 movement across the rectal wall in vitro are high enough to explain recovery of phosphate secreted in situ by Malpighian tubules of starved locusts. The location and possible mechanism of PO 4 transport are discussed.