The essential role of cytosolic Cl- in Ca2+ regulation of an amiloride-sensitive channel in fetal rat pneumocyte.
An amiloride-sensitive, Ca(2+)-activated nonselective cation (NSC) channel in the apical membrane of fetal rat alveolar epithelium plays an important role in stimulation of Na+ transport by a beta adrenergic agonist (beta agonist). We studied whether Ca2+ has an essential role in the stimulation of the NSC channel by beta agonists. In cell-attached patches formed on the epithelium, terbutaline, a beta agonist, increased the open probability (Po) of the NSC channel to 0.62 +/- 0.07 from 0.03 +/- 0.01 (mean +/- SE; n = 8) 30 min after application of terbutaline in a solution containing 1 mM Ca2+. The Po of the terbutaline-stimulated NSC channel was diminished in the absence of extracellular Ca2+ to 0.26 +/- 0.05 (n = 8). The cytosolic Ca2+ concentration ([Ca2+]c) in the presence and absence of extracellular Ca2+ was, respectively, 100 +/- 6 and 20 +/- 2 nM (n = 7) 30 min after application of terbutaline. The cytosolic Cl- concentration ([Cl-]c) in the presence and absence of extracellular Ca2+ was, respectively, 20 +/- 1 and 40 +/- 2 mM (n = 7) 30 min after application of terbutaline. The diminution of [Ca2+]c from 100 to 20 nM itself had no significant effects on the Po if the [Cl-]c was reduced to 20 mM; the Po was 0.58 +/- 0.10 at 100 nM [Ca2+]c and 0.55 +/- 0.09 at 20 nM [Ca2+]c (n = 8) with 20 mM [Cl-]c in inside-out patches. On the other hand, the Po (0.28 +/- 0.10) at 20 nM [Ca2+]c with 40 mM [Cl-]c was significantly lower than that (0.58 +/- 0.10; P < 0.01; n = 8) at 100 nM [Ca2+]c with 20 mM [Cl-]c' suggesting that reduction of [Cl-]c is an important factor stimulating the NSC channel. These observations indicate that the extracellular Ca2+ plays an important role in the stimulatory action of beta agonist on the NSC channel via reduction of [Cl-]c.
Marunaka
Y
Y
Department of Cellular and Molecular Physiology, Kyoto Prefectural University of Medicine, Kyoto 602-0841, Japan.
Niisato
N
N
D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000502:physiology*; D002712:Chlorides / Q000502:physiology*; D003600:Cytosol / Q000502:physiology; D004847:Epithelial Cells / Q000502:physiology; D005333:Fetus / Q000166:cytology; D007473:Ion Channels / Q000819:agonists / Q000502:physiology*; D011650:Pulmonary Alveoli / Q000166:cytology / Q000196:embryology / Q000502:physiology*; D051381:Rats; D020545:Respiratory Mucosa / Q000502:physiology*; D013726:Terbutaline / Q000494:pharmacology
D000318:Adrenergic beta-Agonists; D002712:Chlorides; D007473:Ion Channels; D000584:Amiloride; D013726:Terbutaline; D002118:Calcium