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

• Published in: American journal of physiology. Lung cellular and molecular physiology 2004-12, Vol.287 (6), p.L1284-L1292
• Main Authors: Mair, Norbert, Frick, Manfred, Bertocchi, Cristina, Haller, Thomas, Amberger, Albert, Weiss, Helmut, Margreiter, Raimund, Streif, Werner, Dietl, Paul
• Format: Article
• Language: English
• Subjects: Adenosine Diphosphate - pharmacology; Adenosine Monophosphate - pharmacology; Adenosine Triphosphate - pharmacology; Animals; Cadmium - pharmacology; Calcium - physiology; Cation Transport Proteins - drug effects; Cation Transport Proteins - physiology; Cations, Divalent - pharmacology; Cell Adhesion; Cytosol - physiology; DNA Primers; Humans; Male; Manganese - pharmacology; Membrane Potentials - drug effects; Membrane Potentials - physiology; Pulmonary Alveoli - cytology; Pulmonary Alveoli - drug effects; Pulmonary Alveoli - physiology; Rats; Rats, Sprague-Dawley; Reverse Transcriptase Polymerase Chain Reaction; Strontium - pharmacology
• ISSN: 1040-0605; 1522-1504
• DOI: 10.1152/ajplung.00177.2004

Departments of 1 Physiology, 3 General and Transplant Surgery, and 4 Pediatrics, Medical University of Innsbruck, and 2 Tyrolean 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 Ca 2+ 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 – , Ca 2+ , and Mg 2+ . It was blocked by adenosine nucleotides (cytoplasmic side) with the following order of potency: AMP ADP (EC 50 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. Cd 2+ blocked the channel with an EC 50 55.5 nM. We conclude that type II cells express a Ca 2+ -dependent, nucleotide-inhibited, nonselective, and Ca 2+ -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 Address for reprint requests and other correspondence: P. Dietl, Dept. of Physiology, Medical Univ. of Innsbruck, Fritz-Pregl-Str. 3, A-6020 Innsbruck, Austria (E-mail: paul.dietl{at}uibk.ac.at )