QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by CHAO, A. C. Articles by KOCH, A. Search for Related Content PubMed Articles by CHAO, A. C. Articles by KOCH, A.

Journal of Experimental Biology 155,403-414 (1991)
Published by Company of Biologists 1991

Cytoplasmic pH and Goblet Cavity pH in the Posterior Midgut of the Tobacco Hornworm Manduca Sexta

ANTHONY C. CHAO ¹, DAVID F. MOFFETT ², and ALAN KOCH ²

¹ Laboratory for Molecular Physiology, Zoophysiology Program, Washington State University, Pullman, WA 99164-4220, USA; Cardiovascular Research Institute, University of California, San Francisco, CA 94143-0532, USA
² Laboratory for Molecular Physiology, Zoophysiology Program, Washington State University, Pullman, WA 99164-4220, USA

To whom reprint requests should be sent

In the larval lepidopteran midgut, the major energy-requiring step of transepithelial K⁺ secretion occurs across the goblet cell apical membrane. Studies of vesicles of goblet cell apical membrane suggest that K⁺ secretion across this membrane is a secondary active process in which electroneutral K⁺/H⁺ antiport is driven by primary electrogenic H⁺ secretion. Transbasal K⁺ movement is thermodynamically passive under standard conditions, but the presence of an active process is revealed in hypoxic solutions or at low extracellular K⁺ concentration.

We measured the pH of cytoplasm and goblet cell cavities, together with the corresponding transmembrane voltages, using double-barreled pH and voltagesensing microelectrodes. For short-circuited midguts in standard bathing solution (pH 8.0) the weighted mean of cytoplasmic pH was 7.14±0.06 (mean±S.E.M.), an average of 0.34 units more acid than expected for electrochemical equilibrium with the hemolymphal solution. The mean pH of goblet cavities was 7.23±0.11, 1.62 units more acid than expected for equilibrium with the luminal solution. The pH gradient across the goblet cell apical membrane is thus of the wrong polarity to drive K⁺ secretion by electroneutral K⁺/H⁺ antiport; however, if the exchange ratio were two or more H⁺ per K⁺, the cavity-positive electrical potential could drive H⁺ back to the goblet cell cytoplasm coupled to K⁺ secretion from cytoplasm to the goblet cavity.

Insensitivity of the goblet cavity pH to the change in the transvalve voltage caused by open-circuiting suggests either that the goblet cavity pH is well regulated or that the valve connecting the cavity to the gut lumen poses a significant barrier to protons. Transbasal potential and cytoplasmic pH were insensitive to a decrease of hemolymphal pH to 6.8, suggesting that the basal membrane is relatively nonconductive to H⁺. Intracellular pH was unaffected by a decrease of hemolymphal K⁺ to 5 mmol l^-1, suggesting that K⁺/H⁺ exchange is not important for transbasal K⁺ uptake.

Key words: lepidopteran insect midgut, K⁺ transport, intracellular pH, H⁺ transport, H⁺- selective microelectrode, Manduca sexta

Accepted on July 31, 1990

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]

				B. Giordana, M. G. Leonardi, M. Casartelli, P. Consonni, and P. Parenti K+-neutral amino acid symport of Bombyx mori larval midgut: a system operative in extreme conditions Am J Physiol Regulatory Integrative Comp Physiol, May 1, 1998; 274(5): R1361 - R1371. [Abstract] [Full Text] [PDF]