Cl− Currents Activated by Extracellular Nucleotides in Human Bronchial Cells

Cl− Currents Activated by Extracellular Nucleotides in Human Bronchial Cells The perforated-patch technique was used to study the response of human bronchial cells to extracellular nucleotides. ATP or UTP (100 μm) elicited a complex response consisting of a large transient membrane current increase followed by a relatively small sustained level. These two phases were characterized by different current kinetics. Throughout the transient phase (2–3 min) the membrane current (I p ) displayed slow activation and deactivation kinetics at depolarizing and hyperpolarizing potentials respectively. At steady-state (I s ) the relaxation at hyperpolarizing potential disappeared whereas at positive membrane potentials the current became slightly deactivating. The I s amplitude was dependent on the extracellular Ca2+ concentration, being completely inhibited in Ca2+-free medium. Cell pre-incubation with the membrane-permeable chelating agent BAPTA/AM prevented completely the response to nucleotides, thus suggesting that both I p and I s were dependent on intracellular Ca2+. The presence of a hypertonic medium during nucleotide stimulation abolished I s leaving I p unchanged. On the contrary, niflumic acid, a blocker of Ca2+-activated Cl− channels, prevented completely I p without reducing significantly I s . 1,9-dideoxyforskolin fully inhibited I s but also reduced I p . Replacement of extracellular Cl− with aspartate demonstrated that the currents activated by nucleotides were Cl− selective. I p resulted five times more Cl− selective than I s with respect to aspartate. Taken together, our results indicate that ATP and UTP activate two types of Cl− currents through a Ca2+-dependent mechanism. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of Membrane Biology Springer Journals

Cl− Currents Activated by Extracellular Nucleotides in Human Bronchial Cells

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Publisher
Springer-Verlag
Copyright
Copyright © Inc. by 1997 Springer-Verlag New York
Subject
Life Sciences; Biochemistry, general; Human Physiology
ISSN
0022-2631
eISSN
1432-1424
D.O.I.
10.1007/s002329900209
Publisher site
See Article on Publisher Site

Abstract

The perforated-patch technique was used to study the response of human bronchial cells to extracellular nucleotides. ATP or UTP (100 μm) elicited a complex response consisting of a large transient membrane current increase followed by a relatively small sustained level. These two phases were characterized by different current kinetics. Throughout the transient phase (2–3 min) the membrane current (I p ) displayed slow activation and deactivation kinetics at depolarizing and hyperpolarizing potentials respectively. At steady-state (I s ) the relaxation at hyperpolarizing potential disappeared whereas at positive membrane potentials the current became slightly deactivating. The I s amplitude was dependent on the extracellular Ca2+ concentration, being completely inhibited in Ca2+-free medium. Cell pre-incubation with the membrane-permeable chelating agent BAPTA/AM prevented completely the response to nucleotides, thus suggesting that both I p and I s were dependent on intracellular Ca2+. The presence of a hypertonic medium during nucleotide stimulation abolished I s leaving I p unchanged. On the contrary, niflumic acid, a blocker of Ca2+-activated Cl− channels, prevented completely I p without reducing significantly I s . 1,9-dideoxyforskolin fully inhibited I s but also reduced I p . Replacement of extracellular Cl− with aspartate demonstrated that the currents activated by nucleotides were Cl− selective. I p resulted five times more Cl− selective than I s with respect to aspartate. Taken together, our results indicate that ATP and UTP activate two types of Cl− currents through a Ca2+-dependent mechanism.

Journal

The Journal of Membrane BiologySpringer Journals

Published: Apr 1, 1997

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