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.