tailieunhanh - Báo cáo khoa học: Action of palytoxin on apical H+/K+-ATPase in rat colon

Palytoxin stimulated a cation-dependent short-circuit cur-rent (Isc) in rat distal and proximal colon in a concen-tration-dependent fashion when applied to the mucosal surface of the tissue. The distal colon exhibited a higher sensitivity to the toxin. The palytoxin-induced Isc was blocked by vanadate but was resistant to ouabain or scilliroside, suggesting the conversion of a vanadate-sen-sitive H + /K + -ATPase into an electrogenic cation trans-porter. | Eur. J. Biochem. 269 3905-3911 2002 FEBS 2002 doi Action of palytoxin on apical H K -ATPase in rat colon Georgios Scheiner-Bobis1 Thomas Hiibschle2 and Martin Diener2 1 Institute for Biochemistry and Endocrinology 2 Institute for Veterinary Physiology Justus-Liebig-University Giessen Germany Palytoxin stimulated a cation-dependent short-circuit current Isc in rat distal and proximal colon in a concentration-dependent fashion when applied to the mucosal surface of the tissue. The distal colon exhibited a higher sensitivity to the toxin. The palytoxin-induced Isc was blocked by vanadate but was resistant to ouabain or scilliroside suggesting the conversion of a vanadate-sensitive H K -ATPase into an electrogenic cation transporter. Cation substitution experiments with basolaterally depolarized tissues suggested an apparent permeability of the palytoxin-induced conductance of Na K Li . Immunohistochemical control experiments confirmed the absence of the Na K -ATPase in the apical membrane. Consequently the pore-forming action of palytoxin is not restricted to Na K -ATPase but is also observed with the colonic H K -ATPase. Keywords ATPase colon palytoxin Isc ion channel. P2C-type ATPases are oligomeric enzymes consisting of a and b subunits 1 . The sodium pump from the plasma membranes of animal cells a member of this group generates a sodium gradient by pumping three Na ions out of the cell and two K ions into the cell for each ATP hydrolyzed 2 . This sodium gradient is the driving force of all secondarily active transporters and a presupposition for neuronal conduction of signals. The closest relatives of the sodium pump are the proton pumps from gastric and colon epithelial cells 3 . Although these pumps are not identical they both catalyze an active secretion of protons driven by ATP hydrolysis. Unlike the sodium pump however both proton pumps are electroneutral each transports one K ion from the luminal side into the cytosol for .