Phosphate transport by locust rectum in vitro

Abstract

The rectal cuticle is permeable to H2PO4−, but much less so to HPO42−. Everted rectal sacs of Schistocerca gregaria transport PO4 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 32PO4 into rectal tissue from the lumen is inhibited by arsenate. Much of the 32PO4 is converted to organic forms in the tissue but these do not enter the hemocoel compartment. Net rates of PO4 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 PO4 transport are discussed.