K+/H+ antiport in the tobacco hornworm midgut: the K(+)-transporting component of the K+ pump.
The midgut of the tobacco hornworm secretes K+ across the apical plasma membrane of its goblet cells. This secondary K+ transport results from K+/H+ antiport energized by the proton-motive force generated by a primary, H(+)-transporting plasma membrane V-ATPase. Thus, the lepidopteran midgut constitutes a well-established example of the emerging concept that the proton-motive force is an alternative to the classical sodium-motive force for the energization of animal plasma membranes. K+/H+ antiport in the tobacco hornworm midgut is electrophoretic, exchanging 2H+ for 1K+. Under physiological conditions, it is energized by the voltage component of the proton-motive force. The strong coupling of electrophoretic K+/2H+ antiport with the electrogenic V-ATPase provides, in principle, the minimal device for the alkalization of the midgut lumen to pH values higher than 11. K+/H+ antiport is insensitive to bafilomycin A1, but is inhibited by amiloride or Concanavalin A. Lectin staining of blots after SDS-PAGE revealed several glycosylated polypeptides in the goblet cell apical membrane which are not part of the V-ATPase and thus are candidates for the antiporter protein. Current efforts are focused on the isolation of the K+/H+ antiporter.
Lepier
A
A
Zoologisches Institut der Universität, München, Germany.
Azuma
M
M
Harvey
W R
WR
Wieczorek
H
H
D000595:Amino Acid Sequence; D000818:Animals; D017920:Antiporters / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D001693:Biological Transport, Active; D017931:DNA Primers; D004068:Digestive System Physiological Phenomena; D006801:Humans; D006859:Hydrogen / Q000378:metabolism; D018402:Manduca; D008954:Models, Biological; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D011188:Potassium / Q000378:metabolism*; D027961:Potassium-Hydrogen Antiporters; D017386:Sequence Homology, Amino Acid; D017923:Sodium-Hydrogen Exchangers / Q000737:chemistry / Q000235:genetics; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
D017920:Antiporters; D017931:DNA Primers; D027961:Potassium-Hydrogen Antiporters; D017923:Sodium-Hydrogen Exchangers; C069139:growth factor-activatable Na-H exchanger NHE-1; D006859:Hydrogen; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium