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Journal of Experimental Biology 78,213-223 (1979)
Published by Company of Biologists 1979

Bathing Solution Tonicity and Potassium Transport by the Midgut of the Tobacco Hornworm Manduca Sexta

DAVID F. MOFFETT ¹

¹ Department of Zoology, Washington State University, Pullman, WA 99164

Potassium transport by the isolated midgut of Manduca larvae, as measured by the short circuit current, is inhibited by substitution of small organic solutes (M.W. < 340) for the sucrose normally included in bathing solution formulated for this tissue. Other solutes of molecular weight equal to or greater than sucrose are essentially as effective as sucrose in promoting the short circuit current. Equilibration of midgut in solutions containing the small solute mannitol results in a decrease in the dry weight/wet weight ratio of the tissue, suggesting that the small solutes can penetrate into areas of the tissue which are not accessible to sucrose. Histological studies suggest that sites of swelling in the presence of mannitol include both cytoplasm and goblet cell lumen. The inhibition of the short circuit current is rapidly reversible on return to bathing solution containing sucrose or another large solute. The effect of small solutes probably does not involve compromise of the energy source for potassium transport since oxygen uptake is unchanged in the presence of a small solute.

This article has been cited by other articles:

				W. Zeiske, H. Meyer, and H. Wieczorek Insect midgut K+ secretion: concerted run-down of apical/basolateral transporters with extra-/intracellular acidity J. Exp. Biol., February 15, 2002; 205(4): 463 - 474. [Abstract] [Full Text] [PDF]