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This Article Full Text Full Text (PDF) All Versions of this Article: 287/6/L1284    most recent 00177.2004v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (5) Citing Articles via Google Scholar Google Scholar Articles by Mair, N. Articles by Dietl, P. Search for Related Content PubMed PubMed Citation Articles by Mair, N. Articles by Dietl, P.

Inhibition by cytoplasmic nucleotides of a new cation channel in freshly isolated human and rat type II pneumocytes

Departments of ¹Physiology, ³General and Transplant Surgery, and ⁴Pediatrics, Medical University of Innsbruck, and ²Tyrolean Cancer Research Institute, A-6020 Innsbruck, Austria

Submitted 17 May 2004 ; accepted in final form 12 August 2004

Here we report a 26- to 29-pS cation channel abundantly expressed in freshly isolated and primary cultured type II cells from rat or healthy human lungs. The channel was never spontaneously active in cell-attached patches but could be activated by cell permeabilization with -escin. Excised patch-clamp experiments revealed activation by Ca²⁺ concentrations at the cytoplasmic side in the micromolar range. High concentrations of amiloride (>10 µM) at the extracellular side did not inhibit. The channel was equally permeable for K⁺ and Na⁺ but was essentially impermeable for Cl^–, Ca²⁺, and Mg²⁺. It was blocked by adenosine nucleotides (cytoplasmic side) with the following order of potency: AMP ADP (EC₅₀ 10 µM) > ATP >> adenosine >> cyclic AMP. The blocking effect of ATP was reproduced by its nonhydrolyzable analogs AMPPNP or ATP--S. GTP did not inhibit. Cd²⁺ blocked the channel with an EC₅₀ 55.5 nM. We conclude that type II cells express a Ca²⁺-dependent, nucleotide-inhibited, nonselective, and Ca²⁺-impermeable cation channel (NSC_Ca/AMP) with tonically suppressed activity. RT-PCR confirmed expression of TRPM4b, a channel with functional characteristics almost identical with NSC_Ca/AMP. Potential physiological roles are discussed.

patch clamp; calcium; adenosine 5'-monophosphate; adenosine 5'-diphosphate; adenosine 5'-triphosphate; cadmium; lung; alveolus; nonselective cation channel

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