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 microm) 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 (Ip) displayed slow activation and deactivation kinetics at depolarizing and hyperpolarizing potentials respectively. At steady-state (Is) the relaxation at hyperpolarizing potential disappeared whereas at positive membrane potentials the current became slightly deactivating. The Is 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 Ip and Is were dependent on intracellular Ca2+. The presence of a hypertonic medium during nucleotide stimulation abolished Is leaving Ip unchanged. On the contrary, niflumic acid, a blocker of Ca2+-activated Cl- channels, prevented completely Ip without reducing significantly Is. 1, 9-dideoxyforskolin fully inhibited Is but also reduced Ip. Replacement of extracellular Cl- with aspartate demonstrated that the currents activated by nucleotides were Cl- selective. Ip resulted five times more Cl- selective than Is with respect to aspartate. Taken together, our results indicate that ATP and UTP activate two types of Cl- currents through a Ca2+-dependent mechanism.
Zegarra-Moran
O
O
Laboratorio di Genetica Molecolare, Istituto Giannina Gastini, Genova, I-16148 Italy.
Sacco
O
O
Romano
L
L
Rossi
G A
GA
Galietta
L J
LJ
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D001980:Bronchi / Q000166:cytology / Q000187:drug effects*; D002118:Calcium / Q000502:physiology*; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D002712:Chlorides / Q000378:metabolism*; D005576:Colforsin / Q000031:analogs & derivatives / Q000494:pharmacology; D003550:Cystic Fibrosis / Q000378:metabolism; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004847:Epithelial Cells; D004848:Epithelium / Q000187:drug effects; D005110:Extracellular Space / Q000378:metabolism; D006801:Humans; D007424:Intracellular Fluid / Q000378:metabolism; D017136:Ion Transport / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects; D009544:Niflumic Acid / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D014544:Uridine Triphosphate / Q000494:pharmacology*
D002614:Chelating Agents; D002712:Chlorides; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D005576:Colforsin; D009544:Niflumic Acid; D004533:Egtazic Acid; D000255:Adenosine Triphosphate; C047983:1,9-dideoxyforskolin; D002118:Calcium; D014544:Uridine Triphosphate