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

Departments of ¹Physiology and ²Pediatrics and ³The Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia

Submitted 5 October 2005 ; accepted in final form 6 April 2006

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-µm 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 D₁ and D₂ receptors on the surface of AT1 cells, and single-channel recordings showed that 10 µM dopamine increased Na⁺ channel activity [product of the number of channels and single-channel open probability (NP_o)] from 0.31 ± 0.19 to 0.60 ± 0.21 (P < 0.001). The D₁ receptor antagonist SCH-23390 (10 µM) blocked the stimulatory effect of dopamine on AT1 cells, but the D₂ receptor antagonist sulpiride did not.

AT1 cells; epithelial sodium channel; single-channel recording; Erythrina crystagalli lectin; dopamine D₁ and D₂ receptors

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