Regulation of whole cell currents by cytosolic cAMP, Ca2+, and Cl- in rat fetal distal lung epithelium.
The whole cell patch-clamp technique was used to study ionic conductances in fetal distal lung epithelial (FDLE) cells. In unstimulated FDLE cells, K+ conductances were detected in lowered intracellular Cl- concentration ([Cl-]i, < or = 50 mM). The whole cell currents of FDLE cells were increased by elevation of intracellular Ca2+ concentration ([Ca2+]i) or intracellular adenosine 3',5'-cyclic monophosphate (cAMP) concentration ([cAMP]i). The elevation of [Ca2+]i activated the K+ currents. The amiloride-blockable whole cell currents were activated by [cAMP]i of 1 mM with [Cl-]i of 20 mM and were more frequently detected in the pipette solution without ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) than with it (0.5 mM). When the [Cl-]i was fixed at 50 or 145 mM, however, the increase in these currents was not detected even with cAMP and without EGTA. The amiloride-blockable currents were detected in both the Na+ and K+ pipette solutions. Thus the increase in amiloride-blockable whole cell currents was due to the activation of nonselective cation channels. In FDLE cells treated with terbutaline, which is a beta 2-adrenergic receptor agonist, or forskolin, these currents were detected in the pipette solution containing 20 mM Cl- but were suppressed with time when the pipette solution contained 50 or 145 mM Cl-. It seems likely that maintenance of [Cl-]i at the lowered level is an important requirement for the FDLE cells to activate the amiloride-blockable whole cell currents. It is proposed that cellular mechanisms, such as cell shrinkage, exist to reduce the [Cl-]i in response to cAMP.
Nakahari
T
T
Medical Research Council Group in Lung Development, Hospital for Sick Children Research Institute, Toronto, Ontario, Canada.
Marunaka
Y
Y
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000502:physiology*; D002712:Chlorides / Q000502:physiology*; D000242:Cyclic AMP / Q000494:pharmacology / Q000502:physiology*; D003600:Cytosol / Q000378:metabolism*; D004553:Electric Conductivity; D004848:Epithelium / Q000196:embryology; D005333:Fetus / Q000166:cytology / Q000502:physiology*; D008168:Lung / Q000196:embryology / Q000502:physiology*; D011188:Potassium / Q000502:physiology; D051381:Rats / Q000196:embryology; D017208:Rats, Wistar; D013726:Terbutaline / Q000494:pharmacology
D002712:Chlorides; D000584:Amiloride; D000242:Cyclic AMP; D013726:Terbutaline; D011188:Potassium; D002118:Calcium