What is the role of ATP in the hypertensive carotid body?

Abstract

ATP acting on P2X2/3 receptors within carotid bodies (CBs) underpins chemoreflex hyperreflexia and hypertonicity of sympathetic activity in Spontaneously Hypertensive rats (SHR). As the exact mechanisms remain elusive, we hypothesized either a greater release and/or decreased breakdown of ATP in CBs of SHR versus Wistar rats, and that high concentrations of exogenous ATP in the CB of normotensive rats would produce the sensitised motor responses portrayed by SHRs. Three experiments were performed to investigate the generation, breakdown and physiological responses of ATP in the CB: First, we sought to quantify the amount of ATP released from CBs of male Wistar and SHRs (N=10 for each strain; 4-5 weeks old) using an in vitro colorimetric technique; second, in both strains (Wistar, N=10; SHR, N=12), we used digital droplet polymerase chain reaction (ddPCR) for quantitative analysis of gene expression of six enzymes, which are all involved with the extracellular metabolism of ATP (Enpp1-3, Entpd 2-3, and Nt5e); we also quantified the levels of gene expression for tyrosine hydroxylase (TH) and Panx-1 channel, which are markers for CB type I (or glomus cells) and type-II cells, respectively. Third, we used the working heart-brainstem preparation (WHBP) for analysis of the CB chemoreflex responses evoked by ATP stimulation in Wistar rats (N= 25, 60-80g). Stimulation of CBs was carried out with local intra-arterial injection of potassium cyanide (KCN 20-100 μL, 0.04%; i.a.), and direct intra-CB injection of ATP (10-100 μL, 50 μM - 5 mM) or α, β-methylene ATP (10 μM, 450 μM, and 5mM).Although no rat strain differences in Enpp1 and Entpd2-3 were detected, Enpp2-3 and Nt5e expression were increased in SHR (p<0.05) versus Wistar rats suggesting greater breakdown of ATP in SHR CBs. However, ATP released from the CB at baseline and with KCN stimulation was two-fold greater in SHR (P<0.05). KCN stimulation of the CB, evoked hyperpnoea, bradycardia and sympathoexcitation in Wistar rats, whereas ATP produced hypopnoea/apnoea, repetitive burst discharge of post-inspiratory activity and elevations in both abdominal motor activity and SNA. We found that the ATP-induced hyponoea/apnoea was prevented by ipsilateral nodosectomy suggesting activation of non-CB afferent/s. Microinjecting either ATP or α, β-methylene ATP directly into the CB produced hyperpnoea and sympathoexcitation. Despite upregulation of some ATP degrading enzymes in the SHR, CB release of ATP is higher in this strain and produces activation of respiratory and sympathetic systems. Health Research Council of New Zealand This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.