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Characteristics of 5-HT-containing chemoreceptor cells of the chicken aortic body

Shigeo Ito, Toshio Ohta and Yoshikazu Nakazato

Voltage-dependent and oxygen-sensitive currents in 5-HT-containing epithelioid cells isolated from chicken thoracic aorta were examined using the whole-cell patch clamp technique. 5-HT immunoreactive cells were identified with Neutral Red. The release of 5-HT from chicken thoracic aorta in the presence of excess KCl and veratridine was also examined using HPLC.

At a holding potential of -70 mV with CsCl pipette solution, depolarizing steps between -30 and +60 mV produced inward currents that were blocked by tetrodotoxin (0·2 µM). In the presence of tetrodotoxin and BaCl₂ (5 mM), depolarizing steps evoked slow inward currents that were sensitive to CoCl₂ (2 mM). Nifedipine (1 µM) decreased the currents to 79·4 ± 1·7 %, and -conotoxin GVIA (1 µM) to 20·2 ± 3·8 %.

When KCl pipette solution was used, depolarizing potentials positive to -40 mV caused outward currents that were inhibited by tetraethylammonium chloride. The K⁺ currents evoked by depolarizing steps to +20 mV were reduced to 90·3 ± 0·8 % by hypoxia in five out of seven cells. Two cells failed to respond to hypoxia. The K⁺ current response was partly decreased by Neutral Red (20 µM).

Excess KCl (60 mM) and veratridine (30 µM) both caused the release of 5-HT from aortic strips. 5-HT outputs induced by both stimuli were partly inhibited by nifedipine (1 µM) and by -conotoxin GVIA (1 µM), and were abolished by these drugs in combination and by extracellular Ca²⁺ removal.

These results suggest that epithelioid cells containing 5-HT act as chemoreceptor cells in the chicken aortic body, having voltage-dependent Na⁺, K⁺, and L- and N-type Ca²⁺ channels, and oxygen-sensitive K⁺ channels.

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