Identification and Characterization of Hypoxia Sensitive Kvα Subunits in Pulmonary Neuroepithelial Bodies

Abstract

Pulmonary neuroepithelial bodies (NEB) are composed of innervated clusters of amine and peptide producing cells and are thought to function as hypoxia sensitive airway chemoreceptors. We have shown previously that the plasma membrane of rabbit fetal NEB in culture expresses an O₂ sensing molecular complex composed of O₂ sensitive K⁺ channel coupled to an O₂ sensing protein (NADPH oxidase)(Nature, 1993;365:153). A Shaw-like, outward non-inactivating delayed- rectifier type K⁺ channel, was recorded from NEB cells in both culture and lung slices. This K⁺ channel was decreased by hypoxia (pO₂~20 mmHg), and was sensitive to TEA, 4-AP, and H₂O₂. Another whole cell K⁺ current recorded from NEB in culture exhibited electrophysiological characteristics of a slowly inactivating K⁺ current similar to the one described in Xenopus oocyte expressing Kv3.3a channel and this K⁺ current was increased by H₂O₂. Here we report findings on A-type K₂ currents recorded from NEB in neonatal rabbit lung slice preparation. This slowly inactivating K⁺ current was inhibited by BDS-I (3 μM), specific blocker of Kv3.4 and rheteropodatoxin (HpTx-2; 0.2 μM), specific blocker of Kv4, and also sensitive to hypoxia. Using in situ hybridization method, mRNA for Kv3.4 and Kv4.3 was localized in NEB cells identified by immunostaining for serotonin. Expression of Kv3.4 and Kv4.3 proteins in NEB cells was confirmed by immunohistochemistry using specific antibodies. Multiple subtypes of voltage-dependent K⁺ current are expressed in NEB cells that may function as O₂-sensitive K⁺ channels.