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 preincubation 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.
Original language | English |
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Pages (from-to) | 297-305 |
Number of pages | 9 |
Journal | Journal of Membrane Biology |
Volume | 156 |
Issue number | 3 |
DOIs | |
Publication status | Published - 1997 |
Keywords
- ATP
- Bronchial epithelial cells
- Cl channels
- Cl currents
- Intracellular Ca
- Patch-clamp
- UTP
ASJC Scopus subject areas
- Biophysics
- Physiology
- Cell Biology