Evidence for basolateral Cl- channels as modulators of apical Cl- secretion in pulmonary epithelia of Xenopus laevis.
Pulmonary epithelia of air-breathing vertebrates are covered by a thin, fluid layer that is essential for immune defense and gas diffusion. The composition of this layer is maintained by ion transport mechanisms, including Cl(-) transport. The present study focuses on the function of basolateral Cl(-) channels in Xenopus pulmonary epithelia, since knowledge concerning this issue is limited. Therefore, Ussing chamber measurements were performed, and transepithelial short-circuit currents (I(SC)) were monitored. Basolateral application of the Cl(-) channel inhibitor N-phenylanthranilic acid (DPC) resulted in an increase of the I(SC), indicating a DPC-sensitive Cl(-) conductance. This observation was confirmed in experiments using an apical-to-basolateral Cl(-) gradient, with and without nystatin (apical side) to permeabilize the epithelia as well as by establishing an iodide gradient. The DPC-sensitive Cl(-) conductance was influenced by procedures interfering with apical Cl(-) secretion. For example, the effect of forskolin was increased when basolateral Cl(-) channels were blocked by the simultaneous application of DPC. Activation of apical Cl(-) secretion by forskolin/IBMX and subsequent DPC application resulted in a significantly reduced DPC effect. Accordingly, DPC led to an increased apical Cl(-) secretion estimated by an increased 5-nitro-2-(3-phenylpropylamino)benzoic acid-sensitive I(SC). Furthermore, inhibition of basolateral anion exchangers responsible for Cl(-) uptake resulted in a decreased DPC-sensitive current. Taken together, we have evidence concerning the function of basolateral Cl(-) channels in Xenopus pulmonary epithelium and that these channels play a significant role in mediating apical Cl(-) secretion involving a novel Cl(-) recycling mechanism across the basolateral membrane.
Institute of Animal Physiology, Justus-Liebig Univ. Giessen, Germany.
Jens
J
Berger
Katrin
K
Richter
Wolfgang G
WG
Clauss
Martin
M
Fronius
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000818:Animals; D016764:Cell Polarity; D018118:Chloride Channels / Q000187:drug effects / Q000378:metabolism*; D027963:Chloride-Bicarbonate Antiporters / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D066298:In Vitro Techniques; D008168:Lung / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008564:Membrane Potentials; D009579:Nitrobenzoates / Q000494:pharmacology; D009761:Nystatin / Q000494:pharmacology; D010539:Permeability; D013997:Time Factors; D014982:Xenopus laevis; D062367:ortho-Aminobenzoates / Q000494:pharmacology
D018118:Chloride Channels; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides; D009579:Nitrobenzoates; D062367:ortho-Aminobenzoates; D009761:Nystatin; D005576:Colforsin; C058176:5-nitro-2-(3-phenylpropylamino)benzoic acid; C001209:fenamic acid; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D015056:1-Methyl-3-isobutylxanthine