Rabbit Carotid Body Research Articles

Low-intensity focused ultrasound combined with microbubbles for non-invasive downregulation of rabbit carotid body activity in the treatment of hypertension.

Targeting the carotid body (CB) is a new approach in treating hypertension. This study investigates the efficacy and safety of ultrasound combined with microbubbles in targeting CB to treat hypertension. Twenty-seven hypertensive rabbits were randomly assigned to three groups: microbubbles only (sham group, n = 11), ultrasound plus microbubbles (LIFU group, n = 11), and bilateral carotid sinus nerve denervation (CSND group, n = 5). Four weeks post-intervention, blood pressure, hypoxic ventilatory response (HVR), blood pressure variability (BPV), heart rate variability (HRV), biochemical indicators, neurohormones, and histopathology were assessed in all groups. The results indicated significant reductions in systolic and diastolic blood pressure in the LIFU and CSND groups post-intervention, along with decreases in BPV, HRV, and catecholamines. HVR results showed a 35.10% reduction in CB activity in the LIFU group compared to the sham group, which was significantly lower than the reduction in the CSND group compared to the sham group (73.85%). Histopathology and transmission electron microscopy confirmed CB damage and cell apoptosis, with immunofluorescence showing a reduction in type I and II cells. In conclusion, LIFU combined with microbubbles can reduce blood pressure by lowering CB and sympathetic nerve activity.

TASK-1 (K2P3) and TASK-3 (K2P9) in Rabbit Carotid Body Glomus Cells.

Glomus cells isolated from rabbit and rat/mouse carotid bodies have been used for many years to study the role of ion channels in hypoxia sensing. Studies show that hypoxia inhibits the inactivating K+ channels (Kv4) in rabbits, but inhibits TASK in rats/mice to elicit the hypoxic response. Because the role of TASK in rabbit glomus cells is not known, we isolated glomus cells from rabbits and studied the expression of TASK mRNA in the whole carotid body (CB), changes in [Ca2+]i and TASK activity. RT-PCR showed that rabbit CB expressed mRNA for TASK-3 and several Kv (Kv2.1, Kv3.1 and Kv3.3). In rabbit glomus cells in which 20 mM KClo elevated [Ca2+], anoxia also elicited a strong rise in [Ca2+]. In cell-attached patches with 140 mM KCl in the pipette, basal openings of ion channels with single-channel conductance levels of 16-pS, 34-pS, and 42-pS were present. TREK-like channels were also observed. In inside-out patches with high [Ca2+]i, BK was activated. The 42-pS channel opened spontaneously and briefly. The 16-pS and 34-pS channels showed properties similar to those of TASK-1 and TASK-3, respectively. TASK activity in cell-attached patches was lower than that in rat glomus cells under identical recording conditions. Hypoxia (~0.5%O2) reduced TASK activity by ~52% and depolarized the cells by ~30 mV. Our results show that the O2-sensitive TASK contributes to the hypoxic response in rabbit glomus cells.

Carotid body chemotransduction gets the human touch

Carotid body chemotransduction gets the human touch

Expression of Neuronal Nitric Oxide Synthase in Rabbit Carotid Body Glomus Cells Regulates Large-Conductance Ca2+-Activated Potassium Currents

Our previous studies show that a decrease in endogenous nitric oxide (NO) is involved in the blunted outward K(+) currents in carotid body (CB) glomus cells from chronic heart failure (CHF) rabbits. In the present study, we measured the effects of the neuronal nitric oxide synthase (nNOS) transgene on the K(+) currents in CB glomus cells from pacing-induced CHF rabbits. Using single-cell real-time RT-PCR and immunofluorescent techniques, we found that nNOS mRNA and protein are expressed in the rabbit CB glomus cells and CHF decreased the expression of nNOS mRNA and protein in CB glomus cells. After 3 days of an adenoviral nNOS (Ad.nNOS) gene transfection, the expression of nNOS protein was increased to the level found in sham CB glomus cells. In whole cell patch-clamp experiments, Ad.nNOS markedly reversed the attenuated K(+) currents in CB glomus cells from CHF rabbits. The specific nNOS inhibitor (S-methyl-l-thiocitrulline [SMTC]) and large-conductance Ca(2+)-activated K(+) (BK) channel blocker (iberiotoxin) fully abolished the effect of Ad.nNOS on the K(+) currents in the CB glomus cells from CHF rabbits. However, neither CHF nor Ad.nNOS altered the protein expression of BK channel alpha-subunit. These results suggest that a decrease of NO induced by an attenuated nNOS activity lowers the activation of the BK channels but not the protein expression of the BK channel alpha-subunit in the CB glomus cells during CHF.

Oxygen‐Sensitive Potassium Channels in Chemoreceptor Cell Physiology

The characterization of the molecular mechanisms involved in low-oxygen chemotransduction has been an active field of research since the first description of an oxygen-sensitive K(+) channel in rabbit carotid body (CB) chemoreceptor cells. As a result, a large number of components of the transduction cascade, from O(2) sensors to O(2)-sensitive ion channels, have been found. Although the endpoints of the process are analogous, the heterogeneity of the elements involved in the different chemoreceptor tissues precludes a unifying theory of hypoxic signaling, and it has been a source of controversy. However, when these molecular constituents of the hypoxic cascade are brought back to their physiological context, it becomes clear that the diversity of mechanisms is necessary to build up an integrated cellular response that demands the concerted action of several O(2) sensors and several effectors.

Identification and Measurement of Carbonic Anhydrase-II Molecule Numbers in the Rat Carotid Body

Carbonic anhydrase (CA) in the carotid body (CB) plays an important role in the maintenance of blood PO2 and PCO2/pH homeostasis by regulating ventilation. It has been observed that the activity of CA in the rabbit CB is stronger under hypoxic conditions than under normoxic and hyperoxic conditions. In conditions of chronic hypoxia, the volume of the CB increases significantly because the number of type I and II cells increases. So far, the number of CA molecules in the CB has not been assessed. We develop a technique to quantify the number of CA molecules in the CB. The CBs were dissected out from 8 rats, immediately frozen with liquid nitrogen, pulverized and centrifuged. The proteins extracted from CB tissue were heat-denatured and separated by electrophoresis on a 12.5% denatured-polyacrylamide gel (SDSPAGE); a 31 kDa protein band was determined which reacted with a rabbit polyclonal antibody specific for rat CA-II in Western blot analysis. The immunoreactive 31 kDa CA-II protein was detected and quantified by laser scanner densitometry using 125I-rProtein A as a tracer. The mean 125I radioactivity emitted by the antibody bound CA-II was 31277 cpm. This value corresponds to 4.57 ng CA-II. When compared with a rat CA-II calibration curve, an average of number of 3.54 x 107 CA-II molecules were quantified for 1 µg of whole CB tissue. This is a sensitive and accurate radioimmunoassay technique and may be useful in future studies on the role of CA-II in different pathophysiologic conditions.

Interplay of angiotensin 1‐7 and angiotensin II in the regulation of voltage‐gated potassium current in the glomus cells of carotid body

Increasing evidence indicates that angiotensin (Ang) II ‐induced outward potassium current (Ik) inhibition in the carotid body (CB) enhances CB chemoreceptor sensitivity. ACE2 has been identified as a critical negative modulator of Ang II bioactivity, counterbalancing the effects of ACE in determining net tissue Ang II levels. This, coupled with the knowledge that ACE2 is a key enzyme in the formation of Ang 1‐7, led us to hypothesize that Ang 1‐7 would oppose Ang II‐induced Ik inhibition in the CB. Immuno blot analysis confirmed that ACE2 and Mas receptor (Ang 1‐7 receptor) protein are expressed in the rabbit CB. Ang 1‐7 (50 nM) enhanced Ik in CB glomus cells by 16 ± 4%. The Mas receptor antagonist A779 (1 μM) inhibited the effects of Ang 1‐7. Ang II (100 nM) reduced Ik by 91 ± 5%. However, in the presence of Ang 1‐7 (50 nM), AngII reduced Ik by only 12 ± 2%. Hypoxia (PO2=40 Torr)‐induced Ik inhibition (24 ± 4%) was also blunted by Ang 1‐7 (10±3%, P <0.05 versus hypoxia alone) in the CB glomus cells. Together, these findings indicate that Ang 1‐7 attenuates the action of Ang II, which might be involved in the regulation of the CB chemoreceptor sensitivity. (NIH PO1‐HL62222)

NO and CO have got to GO for enhanced chemoreceptor sympathoexcitation in heart failure

arterial chemoreceptors located in the carotid body are an important defense mechanism against systemic hypoxemia. Activation of arterial chemoreceptors increases alveolar ventilation and sympathetic outflow to most vascular beds. During acute exposures to hypoxia, the sympathoexcitatory responses

A Role for DPPX Modulating External TEA Sensitivity of Kv4 Channels

Shal-type (Kv4) channels are expressed in a large variety of tissues, where they contribute to transient voltage-dependent K+ currents. Kv4 are the molecular correlate of the A-type current of neurons (ISA), the fast component of ITO current in the heart, and also of the oxygen-sensitive K+ current (KO2) in rabbit carotid body (CB) chemoreceptor cells. The enormous degree of variability in the physiological properties of Kv4-mediated currents can be attributable to the complexity of their regulation together with the large number of ancillary subunits and scaffolding proteins that associate with Kv4 proteins to modify their trafficking and their kinetic properties. Among those, KChIPs and DPPX proteins have been demonstrated to be integral components of ISA and ITO currents, as their coexpression with Kv4 subunits recapitulates the kinetics of native currents. Here, we explore the presence and functional contribution of DPPX to KO2 currents in rabbit CB chemoreceptor cells by using DPPX functional knockdown with siRNA. Additionally, we investigate if the presence of DPPX endows Kv4 channels with new pharmacological properties, as we have observed anomalous tetraethylammonium (TEA) sensitivity in the native KO2 currents. DPPX association with Kv4 channels induced an increased TEA sensitivity both in heterologous expression systems and in CB chemoreceptor cells. Moreover, TEA application to Kv4-DPPX heteromultimers leads to marked kinetic effects that could be explained by an augmented closed-state inactivation. Our data suggest that DPPX proteins are integral components of KO2 currents, and that their association with Kv4 subunits modulate the pharmacological profile of the heteromultimers.

Pronounced depression by propofol on carotid body response to CO2 and K+-induced carotid body activation

Propofol is a commonly used anesthetic agent, and it attenuates hypoxic ventilatory response in humans. Propofol reduce in vivo and in vitro carotid body responses to hypoxia as well as to nicotine in experimental animals. In the present study we examined the effects of propofol on carotid body responses to hypercapnia and K(+)-induced carotid body activation and compared these effects with hypoxia in an in vitro rabbit carotid body preparation. Hypoxia, hypercapnia and potassium increased the carotid sinus nerve activity and propofol attenuated the chemoreceptor responses to all three stimuli. However, the magnitude of propofol-induced attenuation was greater for hypercapnic and K(+)-induced carotid body activation compared to the hypoxic response. These observations suggest that propofol-induced attenuation of the hypoxic response is partly secondary to depression of chemoreceptor response to hypercapnia inhibiting the synergistic interactions between O(2) and CO(2) and may involve CO(2)/H(+) sensitive K(+) channels.

Arterial Chemoreceptors and Sympathetic Nerve Activity

Chronic elevation in sympathetic nerve activity (SNA) is associated with the development and maintenance of certain types of hypertension1 and contributes to the progression of chronic heart failure (CHF).2 The mechanisms involved in sympathetic dysfunction in these disorders appear to be complex and multifactorial. A unified hypothesis is likely to encompass alterations in multiple autonomic reflex pathways, central integratory sites, and chemical mediators that control sympathetic outflow. For example, tonic restraint of sympathetic outflow by arterial and cardiopulmonary baroreflexes is depressed in CHF2 and depressed or reset in hypertension.3 Moreover, maladaptive changes also occur in the central nervous system at integrative sites for autonomic control in both disease processes.4,5 It is also clear that sympathoexcitatory cardiac,6 somatic,7 and central/peripheral chemoreceptor reflexes8 are enhanced in CHF and hypertension. Arterial chemoreceptors serve an important regulatory role in the control of alveolar ventilation, but they also exert a powerful influence on cardiovascular function.9 Activation of arterial chemoreceptors by hypoxemia increases sympathetic outflow to systemic vascular beds to compensate for the direct vasodilating effects of hypoxia on these vessels and to redistribute blood flow to essential organs. In this review, we highlight relevant information that implicates the arterial chemoreflex as a contributory mechanism for the sympathetic hyperactivity in CHF and hypertension and illustrate proposed mechanisms for this altered function. Arterial chemoreceptors located in the aortic and carotid bodies (CBs) respond to hypoxemia and hypercapnia. Because central chemoreceptors also respond to hypercapnia, hypoxia is typically used as a specific stimulus to arterial chemoreceptors. In some mammals, such as rats and rabbits, reflex responses to hypoxemia arise solely from the CB, whereas in other species, the aortic chemoreceptor contribution can be significant. However, it is not possible to experimentally separate the relative contribution of the aortic and …

Enhanced sensitivity of Kv channels to hypoxia in the rabbit carotid body in heart failure: role of angiotensin II

Angiotensin II (Ang II) plays an important role in the enhanced chemoreflex function that occurs in congestive heart failure (CHF), but the mechanism of this effect within the carotid body (CB) is not known. We investigated the sensitivity of Ca2+-independent, voltage-gated K+ (Kv) channels to hypoxia in CB glomus cells from CHF rabbits, and whether endogenous angiotensin II (Ang II) modulates this action. Using the conventional whole-cell patch clamp technique, we found that Kv currents (IK) under normoxic conditions were blunted in the CB glomus cells from CHF rabbits compared with sham rabbits. In addition, the inhibition of IK and the decrease of resting membrane potential (RMP) induced by hypoxia were greater in CHF versus sham glomus cells. Ang II, at 100 pM, had no direct effect on IK at constant normoxic PO2, but increased the sensitivity of IK and RMP to hypoxia in sham glomus cells. In CHF glomus cells, an AT1 receptor (AT1R) antagonist, L-158 809 (1 microM), alone did not affect IK at normoxia, but it decreased the sensitivity of IK and RMP to hypoxia. At higher concentrations, Ang II dose dependently (0.1-100 nM) reduced IK under constant normoxic conditions in sham and CHF glomus cells, with threshold concentrations of about 900 and 600 pM, respectively. Immunocytochemical and Western blot assessments demonstrated the down-expression of Kv3.4 but not Kv4.3 channels in CHF glomus cells. These results indicate that: (1) Ang II/AT1R signalling increases the sensitivity of Kv channels to hypoxia in CB glomus cells from CHF rabbits; (2) high concentrations of Ang II (> 1 nM) directly inhibit IK in CB glomus cells from sham and CHF rabbits; (3) changes in Kv channel protein expression (Kv3.4 versus Kv4.3) in the CB glomus cell may contribute to the suppression of IK and enhanced sensitivity of IK to hypoxia in CHF.

Down regulation of Kv3.4 channels by chronic hypoxia increases acute oxygen sensitivity in rabbit carotid body

The carotid body (CB) chemoreceptors participate in the ventilatory responses to acute and chronic hypoxia (CH). Arterial hypoxaemia increases breathing within seconds, and CB chemoreceptors are the principal contributors to this reflex hyperventilatory response. Acute hypoxia induces depolarization of CB chemoreceptors by inhibiting certain K+ channels, but the role of these channels in CH, as in high-altitude acclimatization, is less known. Here we explored the effects of prolonged (24-48 h) hypoxic exposure of rabbit CB chemoreceptor cells in primary cultures on the voltage-dependent K+ currents and on their response to acute hypoxia. We found that CH induces a decrease in the amplitude of outward K+ currents due to a reduction in a fast-inactivating BDS- and highly TEA-sensitive component of the current. In spite of this effect, acute hypoxic inhibition of K+ currents is increased in CH cultures, as well as hypoxia-induced depolarization. These data suggest that downregulation of this component (that does not contribute to the oxygen-sensitive K+ current (IKO2) participates in the hypoxic sensitization. Pharmacological, immunocytochemical and quantitative PCR (qPCR) experiments demonstrate that CH-induced decrease in outward K+ currents is due to a downregulation of the expression of Kv3.4 channels. Taken together, our results suggest that CH sensitization in rabbit CB could be achieved by an increase in the relative contribution of IKO2 to the outward K+ current as a consequence of the decreased expression of the oxygen-insensitive component of the current. We conclude that acute and chronic hypoxia can exert their effects acting on different molecular targets.

Role of voltage‐dependent calcium channels in stimulus–secretion coupling in rabbit carotid body chemoreceptor cells

We have defined Ca2+ channel subtypes expressed in rabbit carotid body (CB) chemoreceptor cells and their participation in the stimulus-evoked catecholamine (CA) release. Ca2+ currents (I(Ca)) activated at -30 mV, peaked at +10 mV and were fully blocked by 200 microm Cd2+. L-type channels (sensitive to 2 microm nisoldipine) activated at -30 mV and carried 21 +/- 2% of total I(Ca). Non-L-type channels activated at potentials positive to -10 mV and carried: N channels (sensitive to 1 microM omega-conotoxin-GVIA) 16 +/- 1% of total I(Ca), P/Q channels (sensitive to 3 microM omega-conotoxin-MVIIC after nisoldipine plus GVIA) 23 +/- 3% of total I(Ca) and R channels (resistant to all blockers combined) 40 +/- 3% of total I(Ca). CA release induced by hypoxia, hypercapnic acidosis, dinitrophenol (DNP) and high K(+)(o) in the intact CB was inhibited by 79-98% by 200 microm Cd2+. Hypoxia, hypercapnic acidosis and DNP, depolarized chemoreceptor cells and eventually generated repetitive action potential discharge. Nisoldipine plus MVIIC nearly abolished the release of CAs induced by hypoxia and hypercapnic acidosis and reduced by 74% that induced by DNP. All these secretory responses were insensitive to GVIA. 30 and 100 mm K(+)(o) brought resting membrane potential (E(m)) of chemoreceptor cells (-48.1 +/- 1.2 mV) to -22.5 and +7.2 mV, respectively. Thirty millimolar K(+)(o)-evoked release was abolished by nisoldipine but that induced by 100 mm K(+)(o) was mediated by activation of L, N, and P/Q channels. Data show that tested stimuli depolarize rabbit CB chemoreceptor cells and elicit CA release through Ca2+ entry via voltage-activated channels. Only L and P/Q channels are tightly coupled to the secretion of CA.

Effect of Propofol on Carotid Body Chemosensitivity and Cholinergic Chemotransduction

Propofol decreases the acute hypoxic ventilatory response in humans and depresses in vivo carotid body chemosensitivity. The mechanisms behind this impaired oxygen sensing and signaling are not understood. Cholinergic transmission is involved in oxygen signaling, and because general anesthetics such as propofol have affinity to neuronal nicotinic acetylcholine receptors, the authors hypothesized that propofol depresses carotid body chemosensitivity and cholinergic signaling. An isolated rabbit carotid body preparation was used. Chemoreceptor activity was recorded from the whole carotid sinus nerve. The effect of propofol on carotid body chemosensitivity was tested at three different degrees of PO2 reduction. Nicotine-induced chemoreceptor response was evaluated using bolus doses of nicotine given before and after propofol 10-500 microM. The contribution of the gamma-aminobutyric acid A receptor complex was tested by addition of gamma-aminobutyric acid A receptor antagonists. Propofol reduced carotid body chemosensitivity; the magnitude of depression was dependent on the reduction in PO2. Furthermore, propofol caused a concentration-dependent (10-500 microM) depression of nicotine-induced chemoreceptor response, with a 50% inhibitory concentration (propofol) of 40 microM. Bicuculline in combination with propofol did not have any additional effect, whereas addition of picrotoxin gave a slightly more pronounced inhibition. It is concluded that propofol impairs carotid body chemosensitivity, the magnitude of depression being dependent on the severity of PO2 reduction, and that propofol causes a concentration-dependent block of cholinergic chemotransduction via the carotid sinus nerve, whereas it seems unlikely that an activation of the gamma-aminobutyric acid A receptor complex is involved in this interaction.

Neuromuscular blocking agents block carotid body neuronal nicotinic acetylcholine receptors

Neuromuscular blocking agents predominantly block muscle type nicotinic acetylcholine receptors as opposed to the neuronal type. However, there is growing evidence that neuromuscular blocking agents have affinity to some neuronal nicotinic acetylcholine receptors. The carotid body chemoreceptor as the essential oxygen-sensing cell, relies on cholinergic signalling. Atracurium and vecuronium impair carotid body chemoreceptor activity during hypoxia. Here, we characterize atracurium and vecuronium as antagonists at nicotinic receptors of the carotid body chemoreceptor. Isolated rabbit carotid body preparations with carotid sinus nerve were used, and chemoreceptor activities were recorded. There was a concentration-dependent reduction in the chemoreceptor responses to nicotine, with an IC 50 to 50 μg nicotine of 3.64 and 1.64 μM and to 500 μg nicotine of 27.00 μM and 7.29 μM for atracurium and vecuronium, respectively. It is concluded that atracurium and vecuronium depress nicotine-induced chemoreceptor responses of the carotid body in a dose-dependent fashion.

Acetylcholine release from the carotid body by hypoxia: evidence for the involvement of autoinhibitory receptors.

The purpose of the present study was to investigate whether hypoxia influences acetylcholine (ACh) release from the rabbit carotid body and, if so, to determine the mechanism(s) associated with this response. ACh is expressed in the rabbit carotid body (5.6 +/- 1.3 pmol/carotid body) as evidenced by electrochemical analysis. Immunocytochemical analysis of the primary cultures of the carotid body with antibody specific to ACh further showed that ACh-like immunoreactivity is localized to many glomus cells. The effect of hypoxia on ACh release was examined in ex vivo carotid bodies harvested from anesthetized rabbits. The basal release of ACh during normoxia ( approximately 150 Torr) averaged 5.9 +/- 0.5 fmol.min-1.carotid body-1. Lowering the Po2 to 90 and 20 Torr progressively decreased ACh release by approximately 15 and approximately 68%, respectively. ACh release returned to the basal value on reoxygenation. Simultaneous monitoring of dopamine showed a sixfold increase in dopamine release during hypoxia. Hypercapnia (21% O2 + 10% CO2) as well as high K+ (100 mM) facilitated ACh release from the carotid body, suggesting that hypoxia-induced inhibition of ACh release is not due to deterioration of the carotid body. Hypoxia had no significant effect on acetylcholinesterase activity in the medium, implying that increased hydrolysis of ACh does not account for hypoxia-induced inhibition of ACh release. In the presence of either atropine (10 microM) or domperidone (10 microM), hypoxia stimulated ACh release. These results demonstrate that glomus cells of the rabbit carotid body express ACh and that hypoxia overall inhibits ACh release via activation of muscarinic and dopaminergic autoinhibitory receptors in the carotid body.

Hypoxia does not uniformly facilitate the release of multiple transmitters from the carotid body.

Studies from diverse species have established that type I cell, the putative oxygen sensing element of the carotid body (CB), expresses a variety of conventional neurotransmitters like acetylcholine (ACh), dopamine (DA), and neuropeptides and unconventional neurotransmitters like NO and CO [for recent reviews see, (Prabhakar 2000; Kumar and Prabhakar 2002)]. An essential step in the initiation of the sensory response of the CB to hypoxia involves the release of one or more of neurotransmitters from type I cells onto apposed sensory nerve endings (Prabhakar 2000). From direct measurement of neurotransmitter release, it has been shown that hypoxia facilitates the release of both DA (Fidone et al. 1982; Bairam et al. 1996; Chen et al. 2000), and substance P (Kim et al. 2001) in the rabbit CB. On the other hand, hypoxia facilitates ACh release in the cat CB (Fitzgerald et al. 1999). However, it has not yet been determined by simultaneous monitoring of several transmitters whether hypoxia in a given species evokes the release of multiple or only a subset of transmitters in the CB.

A reevaluation of the mechanisms involved in the secretion of catecholamine evoked by 2,4-dinitrophenol from chemoreceptor cells of the rabbit carotid body.

Dinitrophenol (2,4 dinitrophenol; DNP) was early identified as a potent stimulant of the carotid body (CB; Shen and Hauss, 1939). DNP acts directly upon chemoreceptor cells promoting an increase in the intracellular calcium concentration and the release of catecholamine (CA); both responses are strongly dependent on the presence of Ca2+and Na+in the extracellular media (Obesoet al.1989; Rocheret al.1991; Buckler and Vaughan-Jones, 1998). The uncoupling effects of DNP have also been studied in chemoreceptor cells: DNP produces an activation of glucose consumption and a decrease in the mitochondrial membrane potential (Obesoet al.1989; Buckler and Vaughan- Jones, 1998). Mitochondrial uncouplers such as DNP, carbonyl cyanide m-chlorophenylhydrazone (CCCP) or carbonylcyanide p-(trifluoromethoxy)- phenylhydrazone (FCCP), are protonophores that produce intracellular acidification in several cell types including chemoreceptor cells (Grinstein and Rothstein, 1986; Tretteret al.1998; Buckler and Vaughan-Jones, 1998; Parket al.2002). An intracellular acidification followed by consecutive activation of Na+/H+and Na+/Ca2+exchanger was proposed by our group as the mechanism that triggers exocitosis during DNP stimulation in the adult rabbit CB (Rocheret al.1991; Gonzalezet al.1994). In rat neonatal chemoreceptor cells, however, it was found that DNP induces membrane depolarization by inhibiting a background, voltage-insensitive, K+current (Buckler and Vaughan-Jones, 1998). In addition to suppress this current, DNP also activates a yet uncharacterized inward current. In this model, an “unknown link” between DNP-induced mitochondrial depolarization and plasmalemmal K+-channels inhibition was put forward. In this paper, we have restudied the effects of DNP on rabbit chemoreceptor cells looking for the presence in this preparation of membrane depolarization. Results show that the secretion of CA induced by DNP in the rabbit CB is mostly the result of the entry of calcium to the cell via depolarization-activated calcium channels. In the discussion we reevaluate our previous data and hypothesis on the mechanism of DNP stimulation of the CB at the light of our new data. Though the nature of the membrane current targeted by DNP in rabbit CB has not been investigated, our results indicate that in adult rabbit CB chemoreceptor cells operate trough similar mechanisms than in neonatal rat CB chemoreceptor cells.KeywordsCalcium ChannelCarotid BodyMembrane ConductanceMitochondrial UncouplerIntracellular AcidificationThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Contribution of dopamine D2 receptors for the cAMP levels at the carotid body.

There is a general consensus that the effects of dopamine at the carotid body (CB) are mediated by activation of both D1and D2 receptor subtypes (Gonzalez et ai. 1994). D1- and D2-like receptors have been defined traditionally by their opposing effects on the enzyme adenylate cyclase (AC), with D1-like (D1 and D5) receptors positively coupled to this enzyme, whereas D2-like (D2 D3 and D4) are either negatively coupled or uncoupled to this effector (Missale et al. 1998). Excitatory effects of exogenous dopamine (1 and 10 μM) on cyclic adenosine 3’,5’-monophosphate (cAMP) production have been described at the rabbit CB equilibrated with hyperoxia and attributed to the activation of D1 receptors (Perez-Garcia et al. 1990; Almaraz et al. 1991). The present work was undertaken to investigate the contribution of D2 receptors to cAMP production at the rat CB in hyperoxia, normoxia and hypoxia.