The Essential Role of Cytosolic Cl- in Ca2+ Regulation of an Amiloride-Sensitive Channel in Fetal Rat Pneumocyte
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- 作者：Y. Marunaka and N. Niisato
- 关键词：Key words ; Single channel current — ; Nonselective cation channel — ; β ; adrenergic agonist — ; Terbutaline — ; Amiloride — ; Alveolar type II cells
- 刊名：Journal of Membrane Biology
- 出版年：2001
- 出版时间：March 2001
- 年：2001
- 卷：180
- 期：1
- 页码：91-99
- 全文大小：573 KB
文摘
An amiloride-sensitive, Ca2+-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 (P o ) of the NSC channel to 0.62 ¡À 0.07 from 0.03 ¡À 0.01 (mean ¡Àse; n= 8) 30 min after application of terbutaline in a solution containing 1 mm Ca2+. The P o of the terbutaline-stimulated NSC channel was diminished in the absence of extracellular Ca2+ to 0.26 ¡À 0.05 (n= 8). The cytosolic Ca2+ concentration ([Ca2+] c ) in the presence and absence of extracellular Ca2+ was, respectively, 100 ¡À 6 and 20 ¡À 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 ¡À 1 and 40 ¡À 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 P o if the [Cl−] c was reduced to 20 mm; the P o was 0.58 ¡À 0.10 at 100 nm [Ca2+] c and 0.55 ¡À 0.09 at 20 nm [Ca2+] c (n= 8) with 20 mm [Cl−] c in inside-out patches. On the other hand, the P o (0.28 ¡À 0.10) at 20 nm [Ca2+] c with 40 mm [Cl−] c was significantly lower than that (0.58 ¡À 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 .