Enhanced adenosine A_2b receptor signaling facilitates stimulus-induced catecholamine secretion in chronically hypoxic carotid body type I cells

Abstract

Chronic hypoxia (CHox) augments chemoafferent activity in sensory fibers innervating carotid body (CB) chemoreceptor type I cells; however, the underlying mechanisms are poorly understood. We tested the hypothesis that enhanced paracrine signaling via adenosine (Ado) A2b receptors is involved. Dissociated rat CB cultures were exposed for 24 h to normoxia (Nox, 21% O2) or CHox (2% O2) or treated with the hypoxia mimetic deferoxamine mesylate (DFX), and catecholamine secretion from type I cells was monitored by amperometry. Catecholamine secretion was more robust in CHox and DFX type I cells than Nox controls after acute exposure to acid hypercapnia (10% CO2, pH 7.1) and high K(+) (75 mM). Exogenous Ado increased catecholamine secretion in a dose-dependent manner, and the EC50 was shifted to the right from ∼21 μM Ado in Nox cells to ∼78 μM in CHox cells. Ado-evoked secretion in Nox and CHox cells was markedly inhibited by MRS-1754, an A2b receptor blocker, but was unaffected by SCH-58261, an A2a receptor blocker. Similarly, MRS-1754, but not SCH-58261, partially inhibited high-K(+)-evoked catecholamine secretion, suggesting a contribution from paracrine activation of A2b receptors by endogenous Ado. CB chemostimuli, acid hypercapnia, and hypoxia elicited a MRS-1754-sensitive rise in intracellular Ca(2+) that was more robust in CHox and DFX than Nox cells. Taken together, these data suggest that paracrine Ado A2b receptor signaling contributes to stimulus-evoked catecholamine secretion in Nox and CHox CB chemoreceptors; however, the effects of Ado are more robust after CHox.

Angiotensin II mobilizes intracellular calcium and activates pannexin‐1 channels in rat carotid body type II cells via AT1 receptors

“…). The absence of cross‐talk from type I to type II cells was confirmed by the lack of a Δ[Ca 2+ ] i response in type II cells during perfusion with the depolarizing stimulus high K + (30 m m ), which stimulates neurosecretion from type I cells in similar CB cultures (Buttigieg & Nurse, ; Livermore & Nurse, ). The ‘ n ’ values reported in the text refer to the number of culture dishes sampled, where the Ca 2+ response of each dish was taken as the mean peak Δ[Ca 2+ ] i value obtained from 10–15 randomly chosen cells.…”

“…In Ca 2+ imaging experiments, type II cells were routinely identified by the presence of a robust increase in intracellular Ca 2+ ( [Ca 2+ ] i ) during exposure to the selective P2Y2 receptor agonist UTP (Xu et al 2003;Tse et al 2012;Zhang et al 2012). The absence of cross-talk from type I to type II cells was confirmed by the lack of a [Ca 2+ ] i response in type II cells during perfusion with the depolarizing stimulus high K + (30 mM), which stimulates neurosecretion from type I cells in similar CB cultures (Buttigieg & Nurse, 2004;Livermore & Nurse, 2013). The 'n' values reported in the text refer to the number of culture dishes sampled, where the Ca 2+ response of each dish was taken as the mean peak [Ca 2+ ] i value obtained from 10-15 randomly chosen cells.…”

Purinergic signalling mediates bidirectional crosstalk between chemoreceptor type I and glial‐like type II cells of the rat carotid body

“…Given the presence of both A 2A and A 2B receptors on rat CB type I cells (Gauda, ; Conde et al . , ; Livermore & Nurse, ), it would appear that after the opening of Panx‐1 channels by P2Y2R ligands adenosine was produced in a spatially restricted zone near high affinity A 2A receptors, and/or the concentration of adenosine reached was not sufficiently high to activate low affinity A 2B receptors (Fredholm et al . ).…”

Adenosine and dopamine oppositely modulate a hyperpolarization‐activated current Ih in chemosensory neurons of the rat carotid body in co‐culture

“…, ; Bairam et al . ; Livermore & Nurse, ). While different, and sometimes conflicting, mechanisms have been proposed to explain the autocrine–paracrine actions of adenosine on rat CB type I cells (Vandier et al .…”