Dopamine activates amiloride-sensitive sodium channels in alveolar type I cells in lung slice preparations

Active Na+ reabsorption by alveolar epithelial cells generates the driving force used to clear fluids from the air space. Using single-channel methods, we examined epithelial Na+ channel (ENaC) activity of alveolar type I (AT1) cells from live 250- to 300-mu m sections of lung tissue, circumventing concerns that protracted cell isolation procedures might compromise the innate transport properties of native lung cells. We used fluorescein-labeled Erythrina crystagalli lectin to positively identify AT1 cells for single-channel patch-clamp analysis. We demonstrated, for the first time, single-channel recordings of highly selective and nonselective amiloride-sensitive ENaC channels (HSC and NSC, respectively) from AT1 cells in situ, with mean conductances of 8.2 +/- 2.5 and 22 +/- 3.2 pS, respectively. Additionally, 25 nM amiloride in the patch electrode blocked Na+ channel activity in AT1 cells. Immunohistochemical studies demonstrated the presence of dopamine D-1 and D-2 receptors on the surface of AT1 cells, and single- channel recordings showed that 10 mu M dopamine increased Na+ channel activity [product of the number of channels and single- channel open probability (NPo)] from 0.31 +/- 0.19 to 0.60 +/- 0.21 (P < 0.001). The D1 receptor antagonist SCH-23390 (10 mu M) blocked the stimulatory effect of dopamine on AT1 cells, but the D2 receptor antagonist sulpiride did not.