AJP - Regulatory, Integrative and Comparative Physiology, Vol 244, Issue 2 163-R175, Copyright © 1983 by American Physiological Society

ARTICLES

Chemiosmotic potassium ion pump of insect epithelia

W. R. Harvey, M. Cioffi and M. G. Wolfersberger

Transporting epithelia of insects are unlike most vertebrate epithelia in that they lack a serosa and possess septate junctions. The Na+/K+ pump is absent and an electrogenic K+ uniport pump is present in such insect epithelia as lepidopteran midgut, dipteran salivary glands, and many Malpighian tubules. The K+ pump is located in the apical plasma membrane and pumps K+ out of the cells. In midgut the transepithelial K+ transport is against a potential difference (PD) in excess of 120 mV and against a 10-fold K+ concentration difference in vivo. The pump uses a K+-modulated ATPase thought to be located in particles called K+ portasomes, which resemble the F1-F0 ATPase of phosphorylating membranes. Like F1-F0 particles the K+ portasomes are located on the cation input, electronegative, ATP-binding side of the membrane and appear to pump two cations for each MgATP2- hydrolyzed. We propose that in K+-transporting epithelia and in phosphorylating membranes running backwards the portasomes orient the binding of ATP with respect to a cation-gated channel in such a way that when MgATP2- is hydrolyzed P-i is separated from MgADP-; the 2 K+ or 2 H+ ions are no longer neutralized and are repelled from the channel to the opposite side of the membrane. We have isolated the K+ portasome-containing goblet cell apical membrane from larval Manduca sexta midgut and are attempting to isolate the K+ portasomes and K+-ATPase.

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				J. A. T. DOW and S. A. DAVIES Integrative Physiology and Functional Genomics of Epithelial Function in a Genetic Model Organism Physiol Rev, July 1, 2003; 83(3): 687 - 729. [Abstract] [Full Text] [PDF]