Expression of P2X2 and P2X3 receptor subunits in rat carotid body afferent neurones: role in chemosensory signalling

Abstract

1. Hypoxic chemotransmission in the rat carotid body (CB) is mediated in part by ATP acting on suramin-sensitive P2X purinoceptors. Here, we use RT-PCR, cloning and sequencing techniques to show P2X2 and P2X3 receptor expression in petrosal neurones, some of which develop functional chemosensory units with CB receptor clusters in co-culture. 2. Single-cell RT-PCR revealed that hypoxia-responsive neurones, identified electrophysiologically in co-culture, expressed both P2X2 and P2X3 mRNA. 3. Isohydric hypercapnia (10 % CO(2); pH 7.4) caused excitation of chemosensory units in co-culture. This excitation depended on chemical transmission, with ATP acting as a co-transmitter, since it was inhibited by reduction of the extracellular Ca(2+):Mg(2+) ratio and by the purinoceptor blocker suramin (50-100 microM). 4. Hypoxia and isohydric hypercapnia could separately excite the same chemosensory unit, and together the two stimuli interacted synergistically. 5. Using confocal immunofluorescence, co-localization of P2X2 and P2X3 protein was demonstrated in many petrosal somas and CB afferent terminals in situ. Taken together, these data indicate that ATP and P2X2-P2X3 purinoceptors play important roles in the peripheral control of respiration by carotid body chemoreceptors.

Carotid chemoafferent activity is not necessary for all phrenic long-term facilitation following acute intermittent hypoxia

“…Carotid chemotransduction is critically dependent upon ATP and (specifically) P2X2 receptor activation (Gourine et al, 2005; Prasad et al, 2001; Rong et al, 2001; Zhang et al, 2000). PPADS attenuated the short-term hypoxic phrenic response by >80%, confirming ATP’s critical role in peripheral chemoreflexes.…”

“…ATP, acting via ionotropic P2X 2 receptors, is a critical neurotransmitter in peripheral chemoreceptor function (Prasad et al, 2001; Rong et al, 2001; Zhang et al, 2000). As such, ATP receptor antagonists that do not cross the blood–brain barrier inhibit carotid chemoafferent activity during hypoxia, while maintaining chemoafferent synaptic connections in the CNS.…”

Cxs and Panx- hemichannels in peripheral and central chemosensing in mammals

“…During hypercapnia, the increase in ATP release occurred 19.5 ± 4.8 ms before the induction of breathing. Based on above evidence, they hypothesized that ATP-mediated afferent transduction may also occur in the central chemoreception (Spyer et al, 2004; Gourine et al, 2005), as is described in peripheral chemoreception (Prasad et al, 2001; Zapata, 2007; Piskuric and Nurse, 2013). …”

Orexin-B Augments Voltage-Gated L-Type Ca²⁺ Current via Protein Kinase C-Mediated Signalling Pathway in Ovine Somatotropes

“…In the present study, we examined the N current using conventional whole-cell patch-clamp configuration. We demonstrated that a CTX-sensitive N current exists in ovine somatotropes, but this current accounts for less than 10% of the total Ca 2+ current, a much smaller proportion than it accounts for in neurons [45]. The T current has been demonstrated in ovine somatotropes and gonadotropes, but is negligible in the GH3/B6 cell line [22, 46, 47].…”