Neurotransmitter secretion from carotid body glomus cells is hypothesized to be an essential element of chemotransduction. To address one aspect of this hypothesis, catecholamine release in response to hypoxic hypoxia and histotoxic hypoxia was examined using electrically treated carbon-fiber microelectrodes placed in rat carotid bodies in vitro. Carotid bodies of mature rats were removed, along with a portion of the sinus nerve, and suspended in oxygenated (95% O2-5% CO2) Ringer saline at 35 degrees C. The microelectrode differential current after a 50-mV step was recorded over the potential range of -300 to +500 mV. In some preparations, a suction electrode applied to the sinus nerve recorded single-fiber chemoreceptor afferent activity. Stimulation by severe hypoxia (Po2 approximately 0-10 Torr for 3 min, n = 10) and cyanide (2 mM for 2 min) caused an increase in sinus nerve activity and an increase in the carbon-fiber electrode current at a potential corresponding to the oxidation potential of dopamine. As measured in the amperometric mode (constant voltage), tissue catecholamine was 0.35 +/- 0.05 microM (n = 6) and increased to 1.64 +/- 0.43 microM by 1 min of severe hypoxia or to 1.06 +/- 0.17 microM at 2 min of moderate hypoxia (Po2 approximately 50 Torr). Exposure to calcium-free Ringer saline before hypoxia ablated the increase in electrode current, and the response was restored after reperfusion with calcium-containing saline. Repeated exposures to hypoxia (3-min duration) every 15 min resulted in significantly smaller nerve and catecholamine responses. By the third hypoxia exposure, nerve and catecholamine responses were diminished by 30-50%.(ABSTRACT TRUNCATED AT 250 WORDS)
Action Potentials Animals