AJP - Lung Cellular and Molecular Physiology, Vol 267, Issue 1 1-L8, Copyright © 1994 by American Physiological Society
Amiloride-sensitive Na+ channels in fetal type II pneumocytes are regulated by G proteins
G. G. MacGregor, R. E. Olver and P. J. Kemp
Department of Child Health, Ninewells Hospital and Medical School, University of Dundee, United Kingdom.
We have used the patch-clamp technique to record single channels in excised
membrane patches from type II pneumocytes freshly isolated from fetal
guinea pig lung by elastase digestion and differential filtration. The
10/56 patches exhibited spontaneous channel activity with a mean open-state
probability (NPo) of 0.5 +/- 0.1. In symmetrical Na(+)-rich solutions, the
channels had a unitary conductance of 11.1 +/- 0.5 pS and showed current
reversal at approximately 0 mV. Superfusing the inner membrane leaflet of
the patch with a K(+)-rich solution resulted in single-channel current
activity with a conductance of 5.6 +/- 0.2 pS being resolved. Current
reversed at +22.1 +/- 1.9 mV, which is compatible with a PNa+/PK+ of 1.8
+/- 0.1. The addition of 0.1 mM guanosine 5'-O-(3-thiotriphosphate) to the
cytoplasmic face of the patch elicited channel activity in 12/31 previously
quiescent patches, whereas, in spontaneously active patches, channel NPo
was increased. Amiloride, in the concentration range 0.4-4 microM, reduced
the frequency of observed spontaneous (or activatable) channel activity,
reduced NPo, and induced flickery channel behavior. No activity was seen in
the presence of 10 microM amiloride in the pipette. This is the first
direct observation of a G protein regulated Na(+)-conductive pathway in
alveolar epithelium, and it may represent one route by which the alveolar
epithelium of the fetus can regulate the Na(+)-driven fluid reabsorption
necessary for the adaptation of the newborn lung to air breathing at birth.
