Chemoreceptor discharges and cytochrome redox changes of the rat carotid body: Role of heme ligands

Abstract

In superfused in vitro rat carotid body, we recorded chemoreceptor discharges and the redox state of cytochromes simultaneously to identify the primary oxygensensing protein controlling transmitter release and electrical activity of the carotid sinus nerve. These parameters were tested under the inf luence of heme ligands such as oxygen, cyanide, 4-(2-aminoethyl)-benzenesulfonyl f luoride, and CO. During stimulation, there was an initial increase in discharge frequency followed by a decline or suppression of activity. Photometric changes lagged and were maintained as nerve activity decreased. Reducing mitochondrial cytochromes by cyanide or prolonged severe hypoxia, suppressed the chemoreceptor discharge. 4-(2-Aminoethyl)-benzenesulfonyl f luoride, a specific inhibitor of the phagocytic cytochrome b 558 , also silenced the chemoreceptors after an initial excitation. CO increased the chemoreceptor discharge under normoxia, an effect inhibited by light, when the cytochromes were not reduced. When the discharges were depressed by severe hypoxia, exposure to light excited the chemoreceptors and the cytochromes were reduced. The rapidity of the chemosensory responses to light and lack of effect on dopamine release from type I cells led us to hypothesize that carotid body type I cells and the apposed nerve endings use different mechanisms for oxygen sensing: the nerve endings generate action potentials in association with membrane heme proteins whereas cytosolic heme proteins signal the redox state, releasing modulators or transmitters from type I cells.

The role of NADPH oxidase in carotid body arterial chemoreceptors

“…In new experiments we have found that AEBSF enhances hypoxia-evoked CSN activity in the rat carotid body (Fig. 5), a result which conflicts with earlier studies (Lahiri et al, 1999). Collectively, these recent findings strongly suggest that ROS generated by Nox enhance maxiK-like currents, and promote cell repolarization.…”

“…Furthermore, certain subunits common to the phagocyte and non-phagocyte forms of the enzyme, including p22 phox , gp91 phox (or a closely related Nox isoform), p47 phox , and p67 phox , have been localized to type I cells by immunocytochemical staining (Kummer and Acker, 1995). The spectral absorption studies of Acker and his colleagues have enhanced the Nox hypothesis by showing that hypoxia reduces an isoform of cytochrome b558 (Lahiri et al, 1999). Also, a specific Nox inhibitor, 4-(2-aminoethyl)-benzenesulfonyl fluoride (AEBSF), was shown to first excite carotid sinus nerve activity, and then block the chemorecptor response to hypoxia (Lahiri et al, 1999).…”

“…The spectral absorption studies of Acker and his colleagues have enhanced the Nox hypothesis by showing that hypoxia reduces an isoform of cytochrome b558 (Lahiri et al, 1999). Also, a specific Nox inhibitor, 4-(2-aminoethyl)-benzenesulfonyl fluoride (AEBSF), was shown to first excite carotid sinus nerve activity, and then block the chemorecptor response to hypoxia (Lahiri et al, 1999).…”

Effect of N-acetyl-cysteine on the hypoxic ventilatory response and erythropoietin production: linkage between plasma thiol redox state and O2 chemosensitivity

“…1,2,[9][10][11][12] The 2 types of O 2 sensors that regulate ventilation and EPO production in response to changes in arterial oxygen concentration are not completely understood and, to some extent, are still the subject of controversy. 1 Although the oxygen sensors for the HVR in the carotid body and in certain other chemoreceptors have been identified as NADPH oxidase isoforms [13][14][15][16][17] (reviewed in Dröge 18 ), the regulation of EPO production was shown to involve activation of the hypoxia-inducible transcription factor (HIF), which depends on redox-sensitive stabilization of its ␣ subunit. 19,20 Oxygensensing involves in this case the oxygen-dependent hydroxylation of a proline residue (HIF-1␣ P564) and the subsequent ubiquitination and degradation of HIF-1␣.…”

Hypoxia induces production of nitric oxide and reactive oxygen species in glomus cells of rat carotid body

“…Candidates for oxygen-sensor molecules in glomus cells include cytochrome aa 3 Mills and Jobsis 1972;Wilson et al 1994), K + -channels (Buckler 1997;Lopez-Barneo 1996;Wyatt et al 1995), and NADPH oxidases generating reactive oxygen species (ROS; Acker et al 1989;Cross et al 1990). These NADPH oxidases and the mitochondrial respiratory chain are sources of ROS, and altered ROS production during hypoxia has been suggested to be part of the intracellular signaling cascade in response to hypoxia (Acker et al 1989(Acker et al , 1992Cross et al 1990;Lahiri et al 1999). Another free radical, nitric oxide (NO), modulates the response of the carotid body to hypoxia, either directly by inhibition of chemoreceptor activity (Iturriaga et al 2000a,b;Prabhakar et al 1993;Prabhakar 1999;Wang et al 1994Wang et al , 1995 or indirectly by affecting vascular tone and, thereby, O 2 delivery (Lahiri et al 2001).…”