Characterization of ion channels and O 2 sensitivity in gill neuroepithelial cells of the anoxia-tolerant goldfish ( Carassius auratus ).

The neuroepithelial cell (NEC) of the fish gill is an important model for O ₂ sensing in vertebrates; however, a complete picture of the chemosensory mechanisms in NECs is lacking, and O ₂ chemoreception in vertebrates that are tolerant to anoxia has not yet been explored. Using whole cell patch-clamp recording, we characterized four types of ion channels in NECs isolated from the anoxia-tolerant goldfish. A Ca ²⁺ -dependent K ⁺ current ( I _KCa ) peaked at ~20 mV, was potentiated by increased intracellular Ca ²⁺ , and was reduced by 100 μM Cd ²⁺ A voltage-dependent inward current in Ba ²⁺ solution, with peak at 0 mV, confirmed the presence of Ca ²⁺ channels. A voltage-dependent K ⁺ current ( I _KV ) was inhibited by 20 mM tetraethylammonium and 5 mM 4-aminopyridine, revealing a background K ⁺ current ( I _KB ) with open rectification. Mean resting membrane potential of -45.2 ± 11.6 mV did not change upon administration of hypoxia (Po ₂  = 11 mmHg), nor were any of the K ⁺ currents sensitive to changes in Po ₂ during whole cell recording. By contrast, when the membrane and cytosol were left undisturbed during fura-2 or FM 1-43 imaging experiments, hypoxia increased intracellular Ca ²⁺ concentration and initiated synaptic vesicle activity. 100 μM Cd ²⁺ and 50 μM nifedipine eliminated uptake of FM 1-43. We conclude that Ca ²⁺ influx via L-type Ca ²⁺ channels is correlated with vesicular activity during hypoxic stimulation. In addition, we suggest that expression of I _KCa in gill NECs is species specific and, in goldfish, may contribute to an attenuated response to acute hypoxia. NEW & NOTEWORTHY This study provides the first physiological characterization of oxygen chemoreceptors from an anoxia-tolerant vertebrate. Neuroepithelial cells (NECs) from the gills of goldfish displayed L-type Ca ²⁺ channels and three types of K ⁺ channels, one of which was dependent upon intracellular Ca ²⁺ Although membrane currents were not inhibited by hypoxia during patch-clamp recording, this study is the first to show that NECs with an undisturbed cytosol responded to hypoxia with increased intracellular Ca ²⁺ and synaptic vesicle activity.
(Copyright © 2017 the American Physiological Society.)