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Journal of Experimental Biology 157,243-256 (1991)
Published by Company of Biologists 1991

Lidocaine and Barium Distinguish Separate Routes of Transbasal K⁺ Uptake in the Posterior Midgut of the Tobacco Hornworm (Manduca Sexta)

DAVID F. MOFFETT ¹ and ALAN KOCH ¹

¹ Laboratory for Molecular Physiology, Zoophysiology Program, Washington State University Pullman, WA 99164-4236, USA

The isolated posterior midgut of the tobacco hornworm maintains a vigorous transepithelial K⁺ transport from the hemolymphal side to the lumen side at a rate accurately measured by its short-circuit current. Previous studies using the K⁺ channel blocker Ba²⁺ suggested that partial inhibition of the short-circuit current by hemolymphal Ba²⁺ was due to blockage of one of at least two parallel transbasal entry routes for K⁺ into the intracellular transport pool. The present studies show that the local anesthetic lidocaine, at a concentration of 5 mmoll^-1 on the hemolymphal side, partly inhibits net transepithelial K⁺ transport. The inhibition is accompanied by hyperpolarization of the basal membrane and an increase in transbasal resistance, suggestive of a block of transbasal K⁺ conductance. The effects of lidocaine and Ba²⁺ are additive, suggesting that the inhibitors distinguish separate, parallel K⁺ uptake processes.

Key words: lepidopteran insect midgut, active K⁺ transport, lidocaine, barium, short-circuit current, microelectrode, Manduca sexta

Accepted on January 17, 1991

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