title: Electrolyte transport through a cation-selective ion channel in large intestinal enterocytes of Xenopus laevis.
abstract: Electrogenic ion transport through the colon epithelium of the African clawed toad (Xenopus laevis) was investigated with electrophysiological methods in vitro. Interest was focused on a previously described phenomenon, that removal of Ca2+ from the mucosal Ringer's solution increases electrogenic sodium absorption. Our results clearly show that Ca2+ removal reveals an apical ion channel that is not a specific Na+ channel, but a non-selective cation channel with an 'apparent' ion selectivity of the order K+ greater than Na+ = Rb+ greater than Cs+ greater than Li+. This Ca2(+)-sensitive current increased linearly with the mucosal pH, and could be inhibited by other divalent cations (Mg2+, Ba2+) and the organic ion channel blockers quinidine and verapamil. The mucosal Ca2+ concentration that induced a half-maximal inhibition of the Ca2(+)-sensitive current was about 1 mumol l-1 and was independent of the mucosal pH. Owing to the high Ca2+ sensitivity, a regulation of the channel conductivity by extracellular Ca2+ is ruled out. It is concluded that this channel, which is almost identical to similar channels found in amphibian skin and bladder, acts as a pathway for cation absorbing or secreting processes. Possibly the binding of extracellular Ca2+ is related to selectivity changes of the Ca2(+)-sensitive ion channel.
authors.affiliation: Institut für Veterinärphysiologie, Freie Universität Berlin, FRG.
authors.forename: R
authors.initials: R
authors.lastname: Krattenmacher
authors.forename: R
authors.initials: R
authors.lastname: Voigt
authors.forename: M
authors.initials: M
authors.lastname: Heinz
authors.forename: W
authors.initials: W
authors.lastname: Clauss
mesh_terms: D000818:Animals; D001692:Biological Transport; D002412:Cations / Q000378:metabolism*; D003106:Colon / Q000378:metabolism*; D004573:Electrolytes / Q000378:metabolism*; D004594:Electrophysiology; D005260:Female; D007473:Ion Channels / Q000378:metabolism*; D008297:Male; D014982:Xenopus laevis
chemical_list: D002412:Cations; D004573:Electrolytes; D007473:Ion Channels