Mechanisms and properties of sodium transport in locust rectum

Steady-state fluxes of 22 Na + were measured as a function of external Na + concentration across locust recta mounted as flat sheets under short-circuit conditions. A net flux [Formula: see text] at all concentrations confirmed that absorption was an active process obeying Michaelis–Menten kinetics with K t of 17 mM and V max of 1.5 to 2.5 μequiv. cm −2 h −1 . [Formula: see text] was not affected by cAMP, was independent of external Cl − levels and stimulated short-circuit current (i.e., Cl − transport), and was partially inhibited by amiloride and ouabain but not by vanadate. Using intracellular electrodes, a small Na + conductance that was not due to cotransport with organic substrates was identified in the apical plasma membrane. A semiquantitative model for Na + absorption in this epithelium is proposed. We surveyed the locust neurosecretory system for water-soluble factors that might control rectal Na + reabsorption.