Effects of chemostimuli on [Ca²⁺]_i responses of rat aortic body type I cells and endogenous local neurons: comparison with carotid body cells

Abstract

Key points• Mammalian aortic bodies (ABs) are putative peripheral chemoreceptor cells presumed to monitor the oxygen content of arterial blood, although their direct chemosensitivity has never been previously demonstrated at the cellular level.• We used Ca 2+ imaging to show for the first time that a variety of stimuli, including hypoxia, isohydric and acidic hypercapnia, and isocapnic acidosis, caused increases in cytosolic [Ca 2+ ] in AB chemoreceptor cells.• We also showed that some local neurons, known to be uniquely associated with these AB paraganglia in situ, generated robust [Ca 2+ ] i responses to these chemostimuli, suggesting that they may subserve a sensory function.• These results will help us better understand how AB cells sense the composition of the blood in their local environment near the heart, and how they communicate with sensory neurons to initiate homeostatic reflexes during situations of low oxygen supply, like anaemia.Abstract Mammalian aortic bodies (ABs) are putative peripheral arterial chemoreceptors whose function remains controversial, partly because information on their cellular physiology is lacking. In this study, we used ratiometric Ca 2+ imaging to investigate for the first time chemosensitivity in short-term cultures of dissociated cells of juvenile rat ABs, located near the junction of the left vagus and recurrent laryngeal nerves. Among the surviving cell population were glomus or type I cell clusters, endogenous local neurons and glia-like cells. A variety of chemostimuli, including hypoxia, isohydric or acidic hypercapnia, and isocapnic acidosis, caused a rise in intracellular [Ca 2+ ] in AB type I cells. The [Ca 2+ ] i responses were indistinguishable from those in carotid body (CB) type I cells grown in parallel cultures from the same animals, and responses to acidic hypercapnia were prevented by the non-specific voltage-gated Ca 2+ channel antagonist, 2 mM Ni 2+ . Furthermore, we identified a subpopulation (∼40%) of glia-like cells in AB cultures that resembled CB type II cells based on their approximately equal sensitivity to ATP and UTP, consistent with the expression of purinergic P2Y2 receptors. Finally, we showed that some local neurons, known to be uniquely associated with these AB paraganglia in situ, generated robust [Ca 2+ ] i responses to these chemostimuli. Thus, these AB type I cells and associated putative type II cells resemble those from the well-studied CB. Unlike the CB, however, they also associate with a special group of endogenous neurons which we propose may subserve a sensory function in local cardiovascular reflexes. Abbreviations AB, aortic body; BBS, bicarbonate-buffered solution; CB, carotid body; GFAP, glial-fibrillary acidic protein; nNOS, neuronal nitric oxide synthase; RLN, recurrent laryngeal nerve; TH, tyrosine hydroxylase; VAChT, vesicular acetylcholine transporter.

P2Y2 receptor activation opens pannexin‐1 channels in rat carotid body type II cells: potential role in amplifying the neurotransmitter ATP

“…1–, Panx‐1 was not expressed in tyrosine hydroxylase (TH)‐positive chemoreceptor glomus or type I cells but, consistent with positive type II cell staining, it was strongly expressed in contiguous cells with processes that appeared to ensheath type I cells ( n = 3). In dissociated CB cultures, type II cells may occur interspersed within glomus cell clusters (GCs), and often as solitary isolated cells near the periphery of the GCs (Nurse & Fearon, 2002; Piskuric & Nurse, 2012). Within GCs in culture, Panx‐1 labelled cells with the expected characteristics of type II cells; this labelling pattern was separate and distinct from TH‐positive type I cells as exemplified in Fig.…”

“…Because rat type II cells express P2Y2 receptors whose activation leads to a rise in cytosolic Ca 2+ (Xu et al . 2003; Piskuric & Nurse, 2012), we tested whether ATP could induce Panx‐1 channel opening and consequently, membrane depolarization. During perforated‐patch whole‐cell recording, random sampling within GCs occasionally revealed cells with type II characteristics as observed in earlier studies (Duchen et al .…”

Enhanced adenosine A2b receptor signaling facilitates stimulus-induced catecholamine secretion in chronically hypoxic carotid body type I cells

“…For example, whereas ϳ31% of Nox cells responded to hypoxia with a detectable (Ͼ20 nM) rise in [Ca 2ϩ ] i , as many as ϳ87% and ϳ74% did so after exposure to CHox and treatment with DFX, respectively. Furthermore, whereas ϳ26% of Nox cells were sensitive to acid hypercapnia, ϳ69% of CHox cells and ϳ50% of DFX cells were sensitive to acid hypercapnia; however, these [Ca 2ϩ ] i measurements are likely to be underestimated because of the pH sensitivity of the dye fura 2 (43). Thus…”

“…[Ca 2ϩ ]i was measured as described in previous studies from this laboratory (43). Briefly, cultured cells were loaded with the fluorescent Ca 2ϩ indicator fura 2-AM (2.5 M) in BBS for 30 min at 37°C in an incubator with an atmosphere of 95% air-5% CO2.…”

The O2-sensing TRPA1 channel illustrates the significance of vagal nerves in cardio-respiratory adaptation to hypoxia

“…In vivo studies using Trpa1-deficient mice showed that hyperoxia-and mild hypoxia (15% O 2 )-induced enhancement of vagal afferent nerve activities is severely impaired by Trpa1 gene knockout. In addition, a variety of stimuli, including hypoxia, have been shown to increase intracellular Ca 2+ concentration in AB chemoreceptor cells (Piskuric & Nurse 2012). Furthermore, some local neurones, including vagal and sensory neurones that are known to be associated with AB paraganglia in situ, generated robust Ca 2+ responses to hypoxia, suggesting that these neurones serve a sensory function in local cardiorespiratory reflexes.…”