Regulation of low-amiloride-affinity sodium channels in alveolar type II cells.
We determined the mechanisms by which beta-agonists increase sodium (Na+) currents across rat alveolar type II (ATII) cells grown in primary culture. When ATII cells were patched in the cell-attached mode using symmetrical Na+ solutions (150 mM Na(+)-glutamate), single-channel currents were observed for holding potentials between -80 and 30 mV (referenced to the pipette solution) with a single-channel conductance of 27 +/- 3 pS, a mean open time (tau 1) of 3.3 +/- 0.15 ms and an open probability (Po) of 0.36 +/- 0.06 (n = 7). Addition of 10 microM terbutaline into the bath increased tau 1 to 6.43 +/- 0.5 ms and Po to 0.62 +/- 0.06 (n = 7) without affecting channel conductance. Single-channel currents with a conductance of 25 +/- 2 pS were also recorded across ATII cells patched in the inside-out mode. Addition of 250 U/ml of protein kinase A (PKA), 1 mM ATP, and 5 mM MgCl2 in the bath solution (150 mM Na(+)-glutamate) increased the single channel tau 1 from 3.26 +/- 0.15 to 7.38 +/- 0.38 and Po from 0.41 +/- 0.06 to 0.72 +/- 0.07 (n = 6) without altering conductance. Addition of 1 microM amiloride or ethylisopropylamiloride (EIPA) in the pipette solution (150 mM Na(+)-glutamate) blocked single-channel activity almost completely. Ionic substitution experiments showed the relative permeability of Na+ to K+ and Na+ to Cl- to be 7:1 and 8:1, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
Yue
G
G
Department of Anesthesiology, University of Alabama, Birmingham 35233.
Shoemaker
R L
RL
Matalon
S
S
D000584:Amiloride / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D001667:Binding, Competitive; D002478:Cells, Cultured; D004594:Electrophysiology; D037102:Lectins; D016676:Macrophages, Alveolar / Q000378:metabolism; D008297:Male; D037121:Plant Lectins; D011650:Pulmonary Alveoli / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D013726:Terbutaline / Q000494:pharmacology
D037102:Lectins; D037121:Plant Lectins; D015222:Sodium Channels; C034551:maclurin; D000584:Amiloride; D013726:Terbutaline; C039614:ethylisopropylamiloride