title: Ca-sensitive sodium absorption in the colon of Xenopus laevis.
abstract: Transepithelial electrogenic Na transport (INa) was investigated in the colon of the frog Xenopus laevis with electrophysiological methods in vitro. The short circuit current (Isc) of the voltage-clamped tissue was 24.2 +/- 1.8 microA.cm-2 (n = 10). About 60% of this current was generated by electrogenic Na transport. Removal of Ca2+ from the mucosal Ringer solution stimulated INa by about 120%. INa was not blockable by amiloride (0.1 mmol.l-1), a specific Na-channel blocker in epithelia, but a fully and reversible inhibition was achieved by mucosal application of 1 mmol.l-1 lanthanum (La3+). No Na-self-inhibition was found, because INa increased linearly with the mucosal Na concentration. A stimulation of INa by antidiuretic hormones was not possible. The analysis of fluctuations in the short circuit current (noise analysis) indicated that Na ions pass the apical cell membrane via a Ca-sensitive ion channel. The results clearly demonstrate that in the colon of Xenopus laevis Na ions are absorbed through Ca-sensitive apical ion channels. They differ considerably in their properties and regulation from the amiloride-sensitive Na channel which is "typically" found in the colon of vertebrates.
authors.affiliation: Institut für Veterinärphysiologie, Freie Universität Berlin.
authors.forename: R
authors.initials: R
authors.lastname: Krattenmacher
authors.forename: R
authors.initials: R
authors.lastname: Voigt
authors.forename: W
authors.initials: W
authors.lastname: Clauss
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D003106:Colon / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D066298:In Vitro Techniques; D007408:Intestinal Absorption / Q000187:drug effects; D007811:Lanthanum / Q000494:pharmacology; D008297:Male; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism; D014982:Xenopus laevis / Q000378:metabolism*
chemical_list: D015220:Calcium Channels; D015222:Sodium Channels; D007811:Lanthanum; D000584:Amiloride; D012964:Sodium; D002118:Calcium