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Amiloride-blockable Ca2+-activated Na+-permeant channels in the fetal distal lung epithelium

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Abstract

The Na+ transport function of alveolar epithelium represents an important mechanism for clearance of fluid in air space at birth. I observed the activity of two types of amiloride-blockable Na+-permeant cation channels in the apical membrane of fetal distal lung epithelium cultured on permeable filters for 2 days after harvesting of the cells from Wistar rats of 20 days' gestation (term = 22 days). One type was a nonselective cation (NSC) channel and had a linear current/voltage (I/V) relationship with a single-channel conductance of 26.9 ± 0.8 pS (n = 5). The other type was highly Na+ selective (i.e. Na+ channel) and had an inwardly rectifyingI/V relationship with a single-channel conductance of 11.8 ± 0.2 pS (n = 5) around resting membrane potential. The NSC channel was more frequently observed (1.37 ± 0.15 per patch membrane;n = 73) than the Na+ channel (0.15 ± 0.40 per patch membrane;n = 73). However, the open probability of the NSC channel was smaller than that of the Na+ channel. Both types of the channels were activated by cytosolic Ca2+, however the sensitivity to cytosolic Ca2+ was much higher in the Na+ channel than in the NSC channel. Furthermore, both types of the channels were blocked by amiloride or benzamil. The half-maximal inhibitory concentration (IC50) of amiloride or benzamil of the Na+ channel was 1–2 μM, while that of NSC channel was less than 1 μM. Both channels were activated by insulin.

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  1. MRC Group in Lung Development and Division of Respiratory Research, The Hospital for Sick Children Research Institute, The university of Toronto Faculty of Medicine, M5G 1X8, Toronto, Ontario, Canada

    Yoshinori Marunaka

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Marunaka, Y. Amiloride-blockable Ca2+-activated Na+-permeant channels in the fetal distal lung epithelium. Pflugers Arch. 431, 748–756 (1996). https://doi.org/10.1007/BF02253839

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  • DOI: https://doi.org/10.1007/BF02253839

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