Effects of fluoride and cholera and pertussis toxins on sensory transduction in the carotid body.

The regulation of the chemoreceptor cell function by G proteins has been studied by measuring the release of 3H-labeled catecholamines ([3H]CA) in carotid bodies (CBs) treated with fluoride, cholera toxin (CTX), and pertussis toxin (PTX). Fluoride augmented the basal release of [3H]CA in a dose- (5-20 mM) and Ca(2+)-dependent manner. Nisoldipine (1 microM) and ethylisopropyl amiloride (EIPA; 10 microM) inhibited this effect by approximately 60%, and both drugs combined inhibited it in full. BAY K 8644 (1 microM) doubled the effect of fluoride. The effects of fluoride on the stimulus-evoked release of [3H]CA varied with the type of stimulus and the duration of the treatment. Simultaneous application of fluoride with the stimulus increased by five times the release evoked by hypoxia and by two times that by K+ and dinitrophenol (DNP). Preincubation with fluoride for 1 h caused an inhibition (approximately 70%) of the release evoked by high K+ and veratridine, whereas that evoked by DNP and low PO2 was still augmented (approximately 2 times). Preincubation (4 h) of the CBs with CTX (3 micrograms/ml) reduced by 54% the release of [3H]CA evoked by 35 mM K+ but did not affect that evoked by low PO2 or DNP. A similar treatment with PTX (1 microgram/ml) affected only the release of [3H]CA evoked by DNP, reducing it by 65%. The data show that fluoride, CTX, and PTX have different effects on the release of [3H]CA evoked by high external K+, DNP, and low PO2, indicating that the stimulus-secretion coupling process for each stimulus is differently regulated by G proteins.